School of Engineering and Science - Jacobs University

Hybrid Organic-Inorganic Polyoxometalates 

Functionalized by Diorganotin Groups 

by 

Firasat Hussain 

A thesis submitted in partial fulfillment 

of the requirements for the degree of 

Doctor of Philosophy 

Approved, Thesis Committee: 

Prof. Ulrich Kortz (Mentor), IUB 

Prof. Ryan M Richards, IUB 

Dr. Michael H Dickman, IUB 

Prof. Michael T Pope 

Georgetown University, U.S.A. 

Prof. Emmanuel Cadot 

Université de Versailles, France 

Date of defense: 19 May 2006 

School of Engineering and Science

To my beloved parents

Abstract 

Polyoxometalates (POMs) are a well-known class of inorganic metal-oxygen clusters 

with an unmatched structural variety combined with a multitude of properties. The search 

for novel POMs is predominantly driven by exciting catalytic, medicinal, material science 

and bioscience applications. However, the mechanism of action of most polyoxoanions is 

not selective towards a specific target. In order to improve selectivity it appears highly 

desirable to attach organic functionalities covalently to the surface of polyoxoanions. 

The hydrolytic stability of the Sn-C bond enables the synthesis of a novel class of 

polyoxoanions via attachment of organometallic functionalities based on Sn(IV) to the 

surface of lacunary polyoxoanion precursors. 

By reacting (CH 3 ) 2 SnCl 2 with Na 9 (α-XW 9 O 33 ) (X = As III , Sb III ) in aqueous acidic 

medium leads to the formation of 2-D solid-state structures with inorganic and organic 

surface, which are rare examples of discrete polyoxoanions. (CsNa 4 {(Sn(CH 3 ) 2 ) 3 O(H 2 O) 4 

(β-AsW 9 O 33 )}·5H 2 O) ∞ (CsNa-1) and the isostructural (CsNa 4 [(Sn(CH 3 ) 2 ) 3 O(H 2 O) 4 ( 

β-SbW 9 O 33 )]·5H 2 O) ∞ (CsNa-2)It has been synthesized and characterized by multinuclear 

NMR spectroscopy, FTIR spectroscopy and elemental analysis. They crystallizes 

in the orthorhombic system, space group P na2 1 , with identical unit cell parameters a = 

26.118(2) Å, b = 16.064(1) Å, c = 13.776(1) Å, and Z = 1. Multinuclear NMR ( 183 W, 

119 Sn, 13 C, 1 H) showed that CsNa-1 and CsNa-2 decomposes in solution leading to the 

monomeric species [{Sn(CH 3 ) 2 (H 2 O) 2 } 3 (β-XW 9 O 33 )] 3− (X = As III (1), Sb III (2). Polyanions 

1 and 2 consist of a (β-XW 9 O 33 ) fragment which is stabilized by three dimethyltin 

fragments. The three dimethyltin groups of 1 and 2 are grafted onto the polyanion via 

two Sn-O(W) bonds involving the terminal O atoms on the side of the hetero atom lone 

pair. This polyanion has a nominal C s symmetry. 

i

Reacting (CH 3 ) 2 SnCl 2 with the superlacunary polyanion [H 2 P 4 W 24 O 94 ] 22− resulted in 

a dimeric hybrid organic-inorganic polyanion, [{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 94 ) 2 ] 36− (3).It has 

been characterized by multinuclear NMR spectroscopy, FTIR spectroscopy and elemental 

analysis. Single-crystal X-ray analysis of K 17 Li 19 [{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 94 ) 2 ]·51H 2 O 

showed that it crystallizes in the tetragonal system, space group P 4 2 /nmc, a = b = 

21.5112(17) Å, c = 27.171(3) Å, Z = 2. Polyanion 3 is composed of two (H 2 P 4 W 24 O 94 ) 

fragments that are linked by four equivalent diorganotin groups. The unprecedented assembly 

3 has D 2d symmetry and contains a hydrophobic pocket at its center. 

The trimeric, hybrid organic-inorganic tungstophophate(V) 

[{Sn(CH 3 ) 2 (OH)} 3 (Sn(CH 3 ) 2 ) 3 {A-PW 9 O 34 } 3 ] 18− (4) has been synthesized in acidic medium. 

It has been characterized by FTIR spectroscopy, elemental analysis and cyclic voltametry. 

Single-crystal X-ray analysis of the compound showed that it crystallizes in rhombohedral 

system, space group R 3m, a = b = 29.7445(7) Å, c = 15.5915(7) Å, Z = 3. The polyanion 

is composed of three (A-α-PW 9 O 34 ) fragments that are linked by six dimethyltin groups, 

where the outer three ones are connected by µ 2 − OH bridges leading to a cyclic core 

which act as a cap leading to a bowl type structure. This arrangement results in a cyclic, 

trimeric, unprecedented polyanion assembly with C 3v symmetry. 

The tetrameric, hybrid organic-inorganic tungstoarsenate(III) [{Sn(CH 3 ) 2 (H 2 O)} 2 

{Sn(CH 3 ) 2 }As 3 (α-AsW 9 O 33 ) 4 ] 12− (5) has been characterized by multinuclear NMR spectroscopy, 

FTIR spectroscopy and elemental analysis. Single-crystal X-ray analysis of the 

compound showed that it crystallizes in the monoclinic system, space group P 21/c, with 

a = 22.612(2) Å, b = 19.954(2) Å, c = 41.099(4) Å, Z = 4. Polyanion 5 is composed of four 

(B-α-AsW 9 O 33 ) fragments that are linked by three dimethyltin groups and three As(III) 

atoms resulting in an unprecedented, chiral polyoxoanion assembly with C 1 symmetry. 

Interaction of (CH 3 ) 2 SnCl 2 with Na 9 [A-XW 9 O 34 ] (X = P V , As V ) in aqueous acidic 

medium resulted in the dodecameric, ball-shaped anions [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 

(A-XW 9 O 34 ) 12 ] 36− (X = P V , As V ) (6-7). They has been characterized by multinuclear 

NMR spectroscopy, FTIR spectroscopy, scanning tunneling microscopy and elemental 

analysis. Both compounds crystallize as mixed cesium-sodium salts and are isomorphous. 

Single crystal Single-crystal X-ray analysis of the compound showed that it crystallizes in 

ii

the cubic system (space group I m¯3 with a = b = c = 32.7441(4) Å, Z = 2 . The spherical 

structure of the polyanion is spectacular in terms of geometry and size (diameter of 30 

Å) and is unprecedented in polyoxotungstate chemistry. This supermolecular assembly 

is composed of 12 trilacunary [A-XW 9 O 34 ] 9− (X= As V , P V ) Keggin fragments which are 

linked by 36 dimethyltin groups [12 inner (CH 3 ) 2 Sn 2+ and 24 outer (CH 3 ) 2 (H 2 O)Sn 2+ 

groups] resulting in a polyanion with T h symmetry. The polyanion contains 1000 atoms 

with a molar mass of around 33000 gmol −1 . 

The bis-phenyltin substituted lone pair containing tungstoarsenate [(C 6 H 5 Sn) 2 As 2 W 19 O 67 

(H 2 O)] 8− (8) has been synthesized and characterized by multinuclear NMR, FTIR spectroscopy 

and elemental analysis. Single-crystal X-ray analysis of 

(NH 4 ) 7 Na[(C 6 H 5 Sn) 2 As 2 W 19 O 67 (H 2 O)]·17.5H 2 O showed that it crystallizes in the monoclinic 

system, space group P 2 1 /c, with, a = 18.3127(17) Å, b = 24.403(2) Å, c = 

22.965(2) Å, β= 106.223(2) ◦ , and Z = 4. Polyanion 8 consists of two B-α-(As III W 9 O 33 ) 

Keggin moieties linked via WO(H 2 O) fragment and two (SnC 6 H 5 ) 3+ groups leading to a 

sandwich-type structure with nominal C 2v symmetry. 

The titanium(IV), disubstituted lone pair containing tungstoarsenate 

[(TiOH) 2 WO(H 2 O)As 2 W 19 O 67 ] 8− (9) has been synthesized and characterized by FTIR 

spectroscopy and elemental analysis. Single-crystal X-ray analysis was carried out on 

Cs 8 [(TiOH) 2 WO(H 2 O)As 2 W 19 O 67 ]·10.5H 2 O which crystallizes in the monoclinic system, 

space group P 2 1 /m , with a = 12.7764(19)Å, b = 19.425(3) Å, c = 18.149(3) Å, 

β=110.23(3) ◦ , and Z = 2. Polyanion (9) consists of two B-α-(As III W 9 O 33 ) Keggin moieties 

linked via one [WO(H 2 O)] 4+ fragment and two Ti 4+ ions leading to a sandwich-type 

structure with nominal C 2v symmetry. 

Interaction of solid TiO(SO 4 ) with K 14 [P 2 W 19 O 69 (OH 2 )] in an aqueous acidic medium 

resulted in a novel, trimeric polyoxometalate . The compound has been characterized 

by FTIR spectroscopy and elemental analysis. Single-crystal X-ray analysis of the compound 

showed that it crystallizes in rhombohedral system, space group R 3m, a = b = 

29.7444(7) Å, c = 13.6254(9) Å, Z = 3. The polyanion (10) is composed of three α- 

Ti 3 PW 9 O 34 Keggin fragments that are linked via Ti-O-Ti bridges leading to a trimeric 

assembly. Interestingly, one of the titanium from each fragment is connected to the phosiii

phate leading to a trimeric-capped type structure with nominal C 3v symmetry. 

Interaction of solid TiO(SO 4 ) with [γ-SiW 10 O 36 ] 8− in an aqueous acidic medium resulted 

in a novel, tetrameric polyoxometalate [β-Ti 2 SiW 10 O 39 ] 4 ] 24− (11).It has been characterized 

by multinuclear NMR spectroscopy, FTIR spectroscopy and elemental analysis. 

Single-crystal X-ray analysis of the compound showed that it crystallizes in monoclinic 

system, space group P 2 1 /n, a = 12.5188(13) Å, b = 18.864(2) Å, c = 41.075(4) Å, β 

= 97.450(2) ◦ Z = 2. The polyanion is composed of four β-Ti 2 SiW 10 O 39 Keggin fragments 

that are linked via Ti-O-Ti bridges leading to a cyclic assembly. The solid-state 

structure of K 24 [(β-Ti 2 SiW 10 O 39 ) 4 ]·50H 2 O shows face-by-face self assembled polyanions 

(K-11) along the crystallographic ‘a’ axis, which leads to a nanotube-like arrangement. 

The cadmium(II)-substituted tungstoarsenate [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− (12) has 

been synthesized and characterized in the solid state by XRD, FTIR spectroscopy, elemental 

analysis and 183 W and 111 Cd NMR spectroscopy. Single crystal X-ray analysis 

of Cs 4 K 3 Na 5 [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ]·20H 2 O (CsKNa-12), shows that it crystallizes in 

the monoclinic system, space group P 2 1 /n, with a = 13.1402(12) Å, b = 19.0642(17) Å, 

c = 17.5666(15) Å, β = 90.274(2) ◦ and Z = 2. Polyanion (9) consists of two lacunary 

[B-α-AsW 9 O 34 ] 10− Keggin moieties linked via a rhomb like (Cd 4 O 14 Cl 2 ) cluster leading to 

a sandwich-type structure. Interestingly, the two external Cd atoms each have a terminal 

Cl ligand, but the derivative have terminal water ligands, [Cd 4 (H 2 O) 2 (B-α-AsW 9 O 34 ) 2 ] 10− 

(13), which has been proved by 183 W and 111 Cd NMR spectroscopy. 

The indium(III)-substituted polyanions [In 3 Cl 2 (B-α-PW 9 O 34 ) 2 ] 11− (14), [In 3 Cl 2 (P 2 W 15 

O 56 ) 2 ] 17− (15), [In 4 (H 2 O) 10 ( β-AsW 9 O 32 OH) 2 ] 4− (16) and [In 4 (H 2 O) 10 (β-SbW 9 O 33 ) 2 ] 6− 

(17) have been synthesized and characterized in the solid state by FTIR spectroscopy 

and elemental analysis and 183 W-NMR. Single-crystal X-ray analysis showed that D,L- 

(NH 4 ) 11 [In 3 Cl 2 (B-α-PW 9 O 34 ) 2 ]·16H 2 O (NH4-14) showed that it crystallizes in the monoclinic 

system, space group P 2 1 /n, with a = 17.5090(10) Å, b = 12.7361(7) Å, c = 

18.7955(11) Å, β = 107.3030(10) ◦ , and Z = 2; 

D,L- (NH 4 ) 9 Na 8 [In 3 Cl 2 (P 2 W 15 O 56 ) 2 ]·39H 2 O (NH4Na-15) crystallizes in the triclinic system, 

space group P ¯1, with a = 13.0643(5) Å, b = 14.8901(6) Å, c = 19.8603(8) Å, α 

= 92.2920(10) ◦ , β = 90.8680(10) ◦ , γ = 100.5630(10) ◦ , and Z = 1; RbNa 3 [In 4 (H 2 O) 10 (βiv

AsW 9 O 32 OH) 2 ]·36H 2 O (RbNa-16) crystallizes in the triclinic system, space group P ¯1, 

with a = 12.8142(5) Å, b = 12.8672(5) Å, c = 16.1794(7) Å, α = 91.1370(10) ◦ , β = 

105.9450(10) ◦ , γ = 104.0980(10) ◦ and Z = 1; K 4 Na 2 [In 4 (H 2 O) 10 (β-SbW 9 O 33 ) 2 ]·30H 2 O 

(KNa-17) crystallizes also in the triclinic system, space group P ¯1, with a = 12.2306(9) 

Å, b = 12.7622(10) Å, c = 16.1639(12) Å, α = 73.9890(10) ◦ , β = 76.5550(10) ◦ , γ = 

86.2130(10) ◦ and Z = 1. Synthesis of polyanions 14-17 have been accomplished by reaction 

of In 3+ ions with the lacunary precursors [B-α-PW 9 O 34 ] 9− , [P 2 W 15 O 56 ] 12− and 

[α-XW 9 O 33 ] 9− (X = As III , Sb III ), respectively, in aqueous, acidic medium. The chiral 

polyanions 14 and 15 are composed of three In(III) ions connected to two (B-α-PW 9 O 34 ) 

and (P 2 W 15 O 56 ) fragments, respectively. Only one of the inner sites of the central rhombus 

is occupied by an indium atom and the two outer indium atoms contain a terminal 

Cl ligand. The structural stability of the polyanions 14-17 in solution were studied by 

31 P and 183 W NMR. 

v

Acknowledgements 

I extend my sincere gratitude and appreciation to many people who made this doctoral 

thesis possible. Special thanks are due to my mentor Prof. Ulrich Kortz for his consistent 

guidance, advice and cooperation. Thanks are also due to my lab mates and heartfelt 

thanks to Mr. Markus Reicke for cooperation in lab work also thanks to Dr. Li-Hua Bi 

for her fruitful suggestions. 

I would like to thank Dr. M. H. Dickman,(IUB) who instructed me on X-ray crystallography, 

starting from all the basics; how to mount a crystal to solving the crystal structure. 

Several compounds were re-collected during the instruction and also compound 10 was 

collected here at IUB in Prof.Ulrich Kortz’s lab. 

I thank my mentor Prof.Ulrich Kortz again who brought valuable gifts (crystal structures) 

from Florida State and Georgetown University, U.S.A. during his visits. X-ray data for 

compounds 1, 3-8,11-17 were collected in the Chemistry department of Florida State 

and Georgetown University, U.S.A. X-ray data for compound 2 was collected during his 

visit to Hamburg University. 

X-ray data for compounds 10 and 20 were collected in Kortz’s lab, IUB. 

Thanks are due to Prof. R. M. Richards,(IUB) for being one of the examiners of the 

thesis. 

I would like to thank Prof. M. T. Pope, (Georgetown University, U.S.A.) for his time to 

time suggestions and also for being an external examiner of the thesis. 

I would like to thank Prof. E. Cadot, (Université de Versailles, France.) for being an 

external examiner of the thesis. 

I would like to thank Prof. M. Winterhalter and his group for HPPS measurements. 

I would like to thank our collaborators Dr. B. Keita, and Prof. L. Nadjo, (Université 

vi

Paris-Sud, Orsay Cedex, France) for electrochemistry studies. 

I would also like to thank our collaborators Prof. P. Müller and his coworkers Mr. M. S. 

Alam, V. Dremov, Physikalisches Institut III, (Universität Erlangen-Nürnberg, Germany) 

for STM studies. 

I am highly indebted to Prof. G. Haerendel for giving me an opportunity to carry out my 

research career in IUB. 

I would also like to acknowledge IUB for the fellowship. 

My special thanks goes to my brother, parents, friends and Katja Knoop (Office secretary) 

for their cooperation, support and encouragement during the time of my studies. 

vii

Table of Contents 

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

i 

xi 

xvi 

1 Introduction 1 

1.1 Historical perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

1.1.1 The clathrate-like structure . . . . . . . . . . . . . . . . . . . . . . 4 

1.1.2 Chemical elements taking part in POMs . . . . . . . . . . . . . . . 4 

1.1.3 Features of POMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

1.2 Geometric Structures of representative types of Polyanions: Keggin, Lindqvist, 

Anderson-Evans and Wells-Dawson . . . . . . . . . . . . . . . . . . . . . . 6 

1.3 Lacunary Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

2 Experimental 18 

2.0.1 Reagents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

2.1 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

2.1.1 Infrared spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

2.1.2 Single crystal X-ray diffraction . . . . . . . . . . . . . . . . . . . . . 18 

2.1.3 Multinuclear magnetic resonance spectroscopy . . . . . . . . . . . . 19 

2.1.4 Cyclic voltametry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

2.1.5 Elemental analyses and thermogravimetric analysis . . . . . . . . . 19 

2.2 Preparation of starting materials . . . . . . . . . . . . . . . . . . . . . . . 20 

2.2.1 Synthesis of Na 9 [AsW 9 O 33 ]·27H 2 O . . . . . . . . . . . . . . . . . . 20 

2.2.2 Synthesis of Na 9 [SbW 9 O 33 ]·27H 2 O . . . . . . . . . . . . . . . . . . . 20 

2.2.3 Synthesis of K 14 [As 2 W 19 O 67·(H 2 O)] . . . . . . . . . . . . . . . . . . 20 

2.2.4 Synthesis of A & B Na 8 [HAsW 9 O 34 ]·11H 2 O (A & B-Type AsW 9 O 34 ) 21 

2.2.5 Synthesis of A-Na 9 [PW 9 O 34 ]·7H 2 O . . . . . . . . . . . . . . . . . . 21 

2.2.6 Synthesis of Cs 6 [P 2 W 5 O 23 ]·H 2 O . . . . . . . . . . . . . . . . . . . . 21 

2.2.7 Synthesis of Cs 7 [PW 10 O 36 ]·H 2 O . . . . . . . . . . . . . . . . . . . . 22 

2.2.8 Synthesis of Na 20 [P 6 W 18 O 79 ]·37.5H 2 O . . . . . . . . . . . . . . . . . 22 

viii

2.2.9 Synthesis of K 12 [H 2 P 2 W 12 O 48 ]·24H 2 O . . . . . . . . . . . . . . . . . 22 

2.2.10 Synthesis of K 16 Li 2 [H 6 P 4 W 24 O 94 ]·33H 2 O . . . . . . . . . . . . . . . 23 

2.2.11 Synthesis of K 28 Li 5 [H 7 P 8 W 48 O 184 ]·92H 2 O . . . . . . . . . . . . . . . 23 

2.2.12 Synthesis of Na 27 [NaAs 4 W 40 O 140 ]·60H 2 O . . . . . . . . . . . . . . . 23 

2.2.13 Synthesis of K 8 [γ-SiW 10 O 36 ]·20H 2 O . . . . . . . . . . . . . . . . . . 23 

2.2.14 Synthesis of K 7 [PW 11 O 39 ]·14H 2 O . . . . . . . . . . . . . . . . . . . 24 

2.2.15 Synthesis of K 14 [P 2 W 19 O 69 (H 2 O)]·24H 2 O . . . . . . . . . . . . . . . 24 

3 Results 26 

3.1 The hybrid organic-inorganic 2-D material 

(CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )]·5H 2 O) ∞ 

(X = As III , Sb III ) and its solution properties . . . . . . . . . . . . . . . . 26 

3.1.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

3.1.2 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . 30 

3.1.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

3.2 The tetrakis-dimethyltin containing 

tungstophosphate ({Sn(CH 3 ) 2 } 4 {H 2 P 4 W 24 O 92 } 2 ) 28− 

evidence for lacunary Preyssler ion . . . . . . . . . . . . . . . . . . . . . . 35 

3.2.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 


3.2.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 

3.3 The trimeric-dimethyltin containing bowl shaped tungstophosphate(V): 

Cs 12 Na 6 {Sn(CH 3 ) 2 (OH)} 3 

(Sn(CH 3 ) 2 ) 3 {A-PW 9 O 34 } 3·14H 2 O . . . . . . . . . . . . . . . . . . . . . . . 44 

3.3.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 


3.3.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 

3.4 The tetrameric, chiral tungstoarsenate(III), 

({Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }As 3 {α-AsW 9 O 33 } 4 ) 21− . . . . . . . . . . . 51 

3.4.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 


3.4.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 

3.5 The gigantic, ball-shaped heteropolytungstates 

({Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-XW 9 O 34 ) 12 ) 36− (X= P V , As V ) . . . . 56 

3.5.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 

3.5.2 Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . 60 

3.5.3 STM studies of Cs-6 . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

3.5.4 HPPS measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 

ix

3.5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 

3.6 The bis-phenyltin substituted, lone pair containing tungstoarsenate: 

({C 6 H 5 Sn} 2 As 2 W 19 O 67 (H 2 O)) 8− . . . . . . . . . . . . . . . . . . . . . . . . 70 

3.6.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 


3.6.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 

3.7 Conclusions and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 

3.7.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 

3.7.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 

3.8 The di-titanium substituted, lone pair containing tungstoarsenate: 

{(TiOH) 2 WO(H 2 O)(B-α-AsW 9 O 33 ) 2 } 8− . . . . . . . . . . . . . . . . . . . 82 

3.8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 

3.8.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 


3.8.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 

3.9 The cyclic trimeric-titanium substituted, 

tungstophosphate: [{Ti 3 O 4 (A-α-PW 9 O 34 )} 3 (PO 4 )] 13− . . . . . . . . . . . . 88 

3.9.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 

3.10 Structural control on the nanomolecular scale: Self- assembly of the polyoxotungstate 

wheel 

({β-Ti 2 SiW 10 O 39 } 4 ) 24− . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 

3.10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 

3.10.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 


3.10.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 

3.11 Structure and solution properties of the 

cadmium(II)-substituted tungstoarsenate: 

(Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ) 12− . . . . . . . . . . . . . . . . . . . . . . . . . . 98 

3.11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 

3.11.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 


3.11.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 

3.12 Some indium(III)-substituted polyoxotungstates of the Keggin and Dawson 

type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 

3.12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 

3.12.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 


3.12.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 

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Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 

NMR Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 

Incomplete Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 

Curriculum Vitae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 

xi

List of Figures 

1.1 Polyhedral models of the three possible unions between two MO 6 octahedral 

units. A) corner-sharing,B) edge-sharing and C) face-sharing . . . . . . . . 3 

1.2 Ball and stick represention of the α Keggin type cluster; the black balls 

represent tungsten and the red balls represent oxygen . . . . . . . . . . . . 5 

1.3 Ball/stick and polyhedral representation of the alpha isomer of the Keggin 

structure with different types of oxygen. Color codes: The blue polyhedra 

represent the tungsten and the red balls represent oxygen . . . . . . . . . . 7 

1.4 Combined polyhedral/ball and stick representation of [Cu 3 Na 3 (H 2 O) 9 (α- 

As III W 9 O 33 ) 2 ] 9− . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

1.5 Combined polyhedral/ball and stick representation of {(O 3 POPO 3 )Mo 6 O 18 } 4− 8 

1.6 Ball and stick representation of the Lindqvist structure . . . . . . . . . . . 9 

1.7 Polyhedron representation of the Anderson structure . . . . . . . . . . . . 9 

1.8 Ball and stick representation of the Wells-Dawson structure . . . . . . . . . 10 

1.9 Schematic representation of the formation of Keggin-type lacunary. Courtesy: 

Dr. Santiago C. Reinoso . . . . . . . . . . . . . . . . . . . . . . . . . 11 

1.10 Schematic representation of the formation of Keggin- and Wells-Dawson 

type lacunary species in tungsto-phosphate system with respect to pH.Courtesy: 

Dr. Santiago C. Reinoso . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

1.11 Monomeric (left) and dimeric species (right) of monoorganotin containing 

polyoxotungstates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

3.1 FTIR spectra of compound CsNa-1(red) and Na 9 [α-AsW 9 O 33 ] (blue) . . 27 

3.2 FTIR spectra of compound CsNa-2(red) and Na 9 [α-SbW 9 O 33 ](blue) . . . 28 

3.3 W 183 NMR spectra of (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 ( β-XW 9 O 33 )]·5H 2 O) 

([X = As (top)CsNa-1, Sb (bottom)CsNa-2] . . . . . . . . . . . . . . . . 30 

3.4 Sn 119 NMR spectra of (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 ( β-XW 9 O 33 )]·5H 2 O) 

[X = As (top)CsNa-1, Sb(bottom)CsNa-2] . . . . . . . . . . . . . . . . . 31 

xii

3.5 Left: combined polyhedral and ball/stick representation of the 2-D solid 

state structure of (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )]·5H 2 O) ∞ (X 

= As, CsNa-1; Sb, CsNa-2). The WO 6 octahedra are purple and the 

balls represent tin (green), arsenic/antimony (blue), oxygen (red) and carbon 

(yellow). Hydrogen atoms are omitted for clarity (left),Right: Side 

view of the 2-D solid state structure of (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β- 

XW 9 O 33 )]·5H 2 O) ∞ (X = As, CsNa-1; Sb, CsNa-2). . . . . . . . . . . . . 32 

3.6 Left:Ball and stick representation of [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )] 3− 

(X = As,1; Sb,2.(A) The balls represent tungsten (black), tin (green), arsenic/antimony 

(blue), oxygen (red), carbon (yellow) and hydrogen (small 

black); Right:Combined polyhedral/ball and stick representation of the 

[{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )] 3− (X = As, 1; Sb, 2).(B) The WO 6 

octahedra are red and the color codes of balls are same as above . . . . . . 33 

3.7 FTIR spectra of compound KLi-3(red) and K 16 Li 2 [H 6 P 4 W 24 O 94 ] (blue) . . 35 

3.8 Ball and stick (left), Polyhedron (right) representation of polyanion 3 . . . 37 

3.9 Ball and stick representation of the asymmetric unit of polyanion 3 . . . . 38 

3.10 Cyclic voltammogram of 2 × 10 −4 M solution of 3 in a pH 4 medium (1 

M CH 3 COOLi + CH 3 COOH). The scan rate was 10 mV.s −1 , the working 

electrode was glassy carbon and the reference electrode was SCE. (A) The 

whole voltammetric pattern(left), (B) The voltammetric pattern restricted 

to the first redox processes (right) . . . . . . . . . . . . . . . . . . . . . . . 40 

3.11 Comparison of the cyclic voltammograms of 2 × 10 −4 M solution of 3 in 

a pH 4 medium (1 M CH 3 COOLi + CH 3 COOH). The scan rate was 10 

mV.s −1 , the working electrode was glassy carbon and the reference electrode 

was SCE. (A) Comparison of the voltammetric patterns of 3 and 

[H 2 P 4 W 24 O 94 ] 22− (left)(B) Comparison of the voltammetric patterns of 3 

and [H 7 P 8 W 48 O 184 ] 33 (right) . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

3.12 FTIR spectra of compound CsNa-4(red) and Na 9 [(A-α-PW 9 O 34 )](blue,) . 44 

3.13 Ball/stick (left) and Polyhedron (right) representation of polyanion 4 . . . 46 

3.14 The central core of Sn(CH 3 ) 2 2+ connected to each other by three (µ 2 -OH) 

bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 

3.15 Cyclic voltammogram of 2 × 10 −4 M solution of 4 in a pH 4 medium (1 

M CH 3 COOLi + CH 3 COOH). The scan rate was 10 mV.s −1 , the working 

electrode was glassy carbon and the reference electrode was SCE. (A) Superposition 

of the CVs restricted to the first redox pattern for trimer and 

A-α-PW 9 O 34 respectively.(left), (B) Complete CV for the trimer showing 

the presence of a second irreversible wave close to the electrolyte discharge. 

(right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 

xiii

3.16 FTIR spectra of compound KNH4-5(red) and Na 9 [α-AsW 9 O 33 ](blue) . . 51 

3.17 Top view of [{Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }As 3 (α -AsW 9 O 33 ) 4 ] 21− (5).(left),the 

unique AsW 9 fragment and its three associated As linkers are not shown for 

clarity.The octahedra represent WO 6 and the balls are tin (green), arsenic 

(yellow), carbon (blue) and oxygen (red). Hydrogen atoms are omitted for 

clarity.(right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 

3.18 Side view of [{Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }As 3 (α-AsW 9 O 33 ) 4 ] 21− The color 

code is the same as in above. . . . . . . . . . . . . . . . . . . . . . . . . . . 54 

3.19 FTIR spectra of compound Cs-6(red) and Na 9 [A-PW 9 O 34 ](blue) . . . . . 57 

3.20 FTIR spectra of compound Cs-7(red)and Na 8 H[A-AsW 9 O 34 ](blue) . . . . 57 

3.21 Ball and stick representation of the asymmetric unit of Cs-6 and Cs-7 

showing the same labeling scheme as both compounds are isostructural . . 59 

3.22 Left:Ball and stick representation of Cs-6 and Cs-7 including the 14 cesium 

counter ions. The color code is as follows: tungsten (black), tin (blue), 

phosphorus/arsenic (yellow), oxygen (red), carbon (green) and cesium (purple). 

No hydrogens are shown for clarity, Right:Polyhedral representation 

of Cs-6 and Cs-7. The WO 6 octahedra are red and the XO 4 tetrahedra 

(X = P, As) are yellow. Otherwise, the labeling scheme is the same as in 

Figure 3.21A. No hydrogens and cesiums shown for clarity . . . . . . . . . 59 

3.23 Representation of the icosahedron spanned by the hetero atoms of Cs-6(P) 

and Cs-7(As) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 

3.24 Left:Representation of the polyhedron spanned by the 12 inner tin atoms of 

6 and 7.Right: Representation of the polyhedron spanned by the 24 outer 

tin atoms of Cs-6 and Cs-7 . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

3.25 Representation of the hexa-capped cube spanned by the 14 cesium ions of 

Cs-6 and Cs-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

3.26 Ball and stick representation of Cs-6 and Cs-7 highlighting the different 

polyhedral shells (12 inner Sn atoms: red, 12 hetero atoms: purple, 24 

outer Sn atoms: yellow)Courtesy: Dr. H. Bögge, University of Bielefeld, 

Germany. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 

3.27 31 P(Left), and 183 W NMR spectra of 

Cs 14 Na 22 {Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ]·149H 2 O . . . . . 63 

3.28 STM pictures of {Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ] 36− . . . . 66 

3.29 Size distribution by intensity and number of polyanion 6 . . . . . . . . . . 67 

3.30 Size distribution by intensity and number of polyanion 7 . . . . . . . . . . 67 

3.31 Size distribution by intensity and number of polyanion Cs-6 . . . . . . . . 68 

3.32 FTIR spectra of compound NH4-8(red) and K 14 [As 2 W 19 O 67 (H 2 O)](blue) . 71 

xiv

3.33 Combined polyhedron and ball/stick representations of [(C 6 H 5 Sn) 2 As 2 W 19 O 67 

(H 2 O)] 8− (left),Top view (right) . . . . . . . . . . . . . . . . . . . . . . . . 72 

3.34 Projection of the crystal packing on the bc plane showing the 2-D arrangement 

of compound 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 

3.35 183 W NMR spectra of compound 8 . . . . . . . . . . . . . . . . . . . . . . 76 

3.36 119 Sn NMR spectra of compound 8 . . . . . . . . . . . . . . . . . . . . . . 76 

3.37 Ball/stick (left), polyhedral (right) representations of 9 . . . . . . . . . . . 84 

3.38 FTIR spectra of compound RbK-10(red) and K 14 [P 2 W 19 O 69 (H 2 O)](blue) 88 

3.39 Ball/stick and polyhedral representation of polyanion 10, color codes: blue 

polyhedra (W), yellow balls (Ti), red balls (O) and pink polyhedra (PO4) 89 

3.40 FTIR spectra of compound K-11(red) and K 8 [γ-SiW 10 O 36 ](blue) . . . . . 92 

3.41 Polyhedral (left) and ball and stick (right) representations of 

({β-Ti 2 SiW 10 O 39 } 4 ) 24− . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 

3.42 Side-view of compound 11 including the potassium ions (purple) inside the 

central cavity (K8) and above and below the cavity (K9, and K9’). . . . . . 94 

3.43 Dimer of Dimer of β(1,10)-Ti 2 (OH) 2 SiW 10 O 38 ] 6− . . . . . . . . . . . . . . . 95 

3.44 FTIR spectra of compound (CsKNa-12)(red) and Na 8 [A-HAsW 9 O 34 ]·11H 2 O 

(blue) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 

3.45 FTIR spectra of compound (CsNa-13)(red) and Na 8 [A-HAsW 9 O 34 ]·11H 2 O 

(blue) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 

3.46 183 W NMR spectra of [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− (12), top, and [Cd 4 (H 2 O) 2 (Bα-AsW 

9 O 34 ) 2 ] 10− (13) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 

3.47 111 Cd NMR spectra of [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− 12, top, and [Cd 4 (H 2 O) 2 (Bα-AsW 

9 O 34 ) 2 ] 10− 13, bottom. . . . . . . . . . . . . . . . . . . . . . . . . . 104 

3.48 Combined polyhedral and ball and stick representation of [Cd 4 Cl 2 (B-α- 

AsW 9 O 34 ) 2 ] 12− . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 

3.49 Combined polyhedral/ball and stick representation of [In 3 Cl 2 (PW 9 O 34 ) 2 ] 11− 

14The red octahedra represent WO 6 , the blue tetrahedra represent PO 4 

and the balls represent indium (green) and chlorine (yellow). . . . . . . . 114 

3.50 183 W NMR spectrum of [In 3 Cl 2 (B-α-PW 9 O 34 ) 2 ] 11− . . . . . . . . . . . . . 116 

3.51 Combined polyhedral/ball and stick representation of [In 3 Cl 2 (P 2 W 15 O 56 ) 2 ] 17− 

15. The color code is the same as in Figure 3.40 . . . . . . . . . . . . . . 116 

3.52 Combined polyhedral/ball and stick representation of 

[In 4 (H 2 O) 10 (β-AsW 9 O 32 OH) 2 ] 4− (16) and [In 4 (H 2 O) 10 (β-SbW 9 O 33 ) 2 ] 6− (17). 

The WO 6 octahedra are shown in red and the balls represent indium 

(green), arsenic/antimony (blue) and water molecules (red). . . . . . . . . 118 

3.53 183 W NMR spectrum of [In 4 (H 2 O) 10 (β-AsW 9 O 32 OH) 2 ] 4− at 293 K . . . . 120 

3.54 13 C NMR spectrum of polyanion 1 . . . . . . . . . . . . . . . . . . . . . . 130 

xv


3.56 31 P NMR spectrum of polyanion 3 . . . . . . . . . . . . . . . . . . . . . . 132 

3.57 119 Sn NMR spectrum of polyanion 3 . . . . . . . . . . . . . . . . . . . . . 133 


3.59 1 H NMR spectrum of polyanion 3 . . . . . . . . . . . . . . . . . . . . . . 135 









3.68 183 W NMR spectrum of polyanion 7 . . . . . . . . . . . . . . . . . . . . . 141 



3.71 119 Sn NMR spectrum of polyanion 8 in presence of sodium chloride . . . . 142 

3.72 FTIR spectra of compound K-18(red) and Na 9 [A-PW 9 O 34 ](blue) . . . . . 143 

3.73 31 P NMR spectrum of polyanion 18 . . . . . . . . . . . . . . . . . . . . . 145 

3.74 Size distribution by intensity of polyanion 18 . . . . . . . . . . . . . . . . 145 

3.75 Size distribution by number of polyanion 18 . . . . . . . . . . . . . . . . . 146 

3.76 Size distribution by volume of polyanion 18 . . . . . . . . . . . . . . . . . 146 

3.77 Ball/stick and polyhedron representation of solid state of 18 showing 1-D 

chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 

3.78 FTIR spectra of compound K-19(red) and K 12 [H 2 P 2 W 12 O 48 ](blue) . . . . 147 

3.79 Ball/stick and polyhedron representation of solid state of 19 showing 1-D 

chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 

3.80 FTIR spectra of compound K-20(red) and K 14 [P 2 W 19 O 69 (H 2 O)](blue) . . 150 

3.81 Ball/stick and polyhedral representation of polyanion 20 . . . . . . . . . . 151 

xvi

List of Tables 

1.1 Selected M-M distances (in angstrom units) of corner- and edgesharing 

octahedra in POMs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

1.2 List of common metal cations, M n+ , taking part in POM frameworks. We 

especially highlight W and Mo for being the most typical as addenda atoms 4 

3.1 Crystal Data and Structure Refinement for compounds CsNa-1 and CsNa- 

2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

3.2 Crystal Data and Structure Refinement for compound KLi-3 . . . . . . . . 36 

3.3 Reduction peak potentials measured from CVs and number (n 1 or n 2 ) of 

electrons corresponding to each wave of 3, [H 2 P 4 W 24 O 94 ] 22− and [H 7 P 8 W 48 O 184 ] 33− 

The scan rate was 10 mV s −1 , the working electrode was glassy carbon and 

the reference electrode was SCE . . . . . . . . . . . . . . . . . . . . . . . . 41 

3.4 Crystal Data and Structure Refinement for compound CsNa-4 . . . . . . 45 

3.5 Crystal Data and Structure Refinement for compound KNH4-5 . . . . . . 52 

3.6 Crystal Data and Structure Refinement for compounds Cs-6 and Cs-7 . . 58 

3.7 Crystal Data and Structure Refinement for compound NH4-8 . . . . . . . 72 

3.8 Crystal Data and Structure Refinement for compound Cs-9 . . . . . . . . 85 

3.9 Crystal Data and Structure Refinement for compound RbK-10 . . . . . . 90 

3.10 Crystal Data and Structure Refinement for compound K-11 . . . . . . . . 93 

3.11 Crystal Data and Structure Refinement for compound CsKNa-12 . . . . . 101 

3.12 Crystal Data and Structure Refinement for compounds NH4-14, NH4Na- 

15, RbNa-16 and KNa-17 . . . . . . . . . . . . . . . . . . . . . . . . . . 113 

3.13 Selected bond lengths and angles in polyanions 14 and 15 . . . . . . . . . 115 

3.14 Selected bond lengths and angles in polyanions 16 and 17 . . . . . . . . . 119 




xvii

Chapter 1 

Introduction 

The great majority of inorganic compounds are constructed of metallic atoms as principal 

entities. Inorganic molecules have great potential because the number of elements 

in purely inorganic molecules, combined with structural diversity, make them more powerful, 

particularly as far as their application is concerned. In fact, the search for new 

properties puts more importance on the elements in a framework than on the structure 

itself. Polyoxometalates (POMs) are polynuclear metal oxygen clusters usually formed of 

Mo, W or V that form a unique class of inorganic compounds because it is unmatched 

in terms of structural versatility and properties [1–6]. They have potential applications 

in many fields including medicine, catalysis, multifunctional materials, chemical analysis, 

imaging, etc. 

1.1 Historical perspectives 

The polyoxometalates have been known since the work of Berzelius [7] on the ammonium 

12-molybdophosphate in 1826, however, the study of polyoxoanion chemistry did not accelerate 

until the discovery of the tungstosilicic acids and their salts by Marignac [8] in 

1862, when analytical compositions of such heteropoly acids were precisely determined. 

Thereafter, the field developed rapidly, so that over 60 different types of heteropoly acids 

(giving rise to several hundred salts) had been described by the first decade of this century. 

Pauling [9] proposed a structure for 12:1 complexes based on an arrangement of twelve 

1

MO 6 octahedra surrounding a central XO 4 tetrahedron. After Pauling’s proposal, in the 

early 1930’s Keggin [10, 11] solved the structure of [H 3 PW 12 O 40 ]·5H 2 O by powder X-ray 

diffraction and showed that the anion was indeed based on WO 6 octahedral units as suggested, 

these octahedra being linked by shared edges as well as corners. The application 

of X-ray crystallography to the determination of polyoxometalate structures accelerated 

the development of polyoxometalate chemistry. 

Polyoxometalates are macro-molecular nanometer sized cluster composed of transition 

metal centers of groups V and VI in high oxidation states (mainly Mo, W and V and 

also Nb and Ta) and normally oxygen atoms. although some derivatives with S,[12–16] 

F, [17] Br [18] and other p-block elements are known. In general, POMs can be described 

as composed of MO n units, where ‘n’ indicates the coordination number of M (n = 4,5,6 

or 7). Usually the distorted octahedral coordination (n = 6)is observed. Apart from M 

and O, other elements (heteroatoms) which are usually labeled as “X” can be part of the 

POM framework. As a general rule, they are tetra or hexa coordinated and lie in the 

center of the M x O y shell. 

According to their composition, the polyoxometalates can be classified in two groups: 

•Isopolyoxometalates, of general formula [ M m O y ] n− , which contain only metal and oxygen. 

•Heteropolyoxometalates, of general formula [X x M m O y ] n− , in addition to metal and oxygen, 

contain another element that acts as a heteroatom. 

In general, restrictions for heteroatoms “X” do not exist, so that around 70 elements from 

all the groups in the periodic Table, except the noble gases, are known to be able to play 

the heteroatom role. Heteroatoms “X” can be classified as: primary, which are essential 

to maintain the structure of the polyanion and therefore, they are not susceptible to 

chemical interchange; secondary, which can be eliminated to generate a stable independent 

polyanion, so that the combination can be considered as a coordination compound 

in which the polyanion acts as a ligand. More specifically, the central heteroatoms in 

Keggin and Wells-Dawson type polyoxometalates can be nonmetallic atom or a transition 

metal atoms which shows tetrahedral geometry. Nevertheless, due to the increasing 

diversity of structures, classified as in the literature, the unequivocal definition of this 

2

group of compounds becomes gradually more and more diffuse. Many reports,[19] books 

[4] and reviews [2, 20] have been published on this topic, showing an enormous molecular 

diversity amongst the inorganic family of molecules. This diversity is a consequence of 

the rich, unprecedented and unusual properties associated to POMs. Many authors claim 

that they can be regarded as packed arrays of pyramidal MO 5 and octahedral MO 6 units. 

These entities are then the fundamental structural units and are somewhat similar to the 

-CH 2 - unit in organic molecules. The very important MO 6 units (and the MO 5 partner 

as well but to a lesser extent) are packed to form countless shapes. They join to one 

another apparently, in accordance with a few simple rules (as -CH 2 - does in organic molecules). 

Observing a representative set of POM clusters and identifying the MO 6 blocks, 

one can notice that the molecule as a whole is built by edge- and/or corner-sharing MO 6 

octahedra. Figure 1.1 shows these simple unions. The most stable unions between two 

Fig. 1.1: Polyhedral models of the three possible unions between two MO 6 octahedral units. A) cornersharing,B) 

edge-sharing and C) face-sharing 

octahedra are the corner- and edge-sharing models,[21–23] in which the M n+ ions are far 

away from each other, and their mutual repulsion is modest (Table 1.1). 

Table 1.1: Selected M-M distances (in angstrom units) of corner- and edgesharing octahedra in POMs. 

Metal(ON) corner-sharing edge-sharing 

W(VI) 3.7 3.4 

Mo(VI) 3.7 3.4 

V(V) 3.5 3.2 

In Figure 1.1C, the MO 6 octahedra are face-sharing, in such a way that the metallic 

centers are closer than in any of the other two cases (A, B) and at such distances, the 

repulsion is not balanced by the stabilization due to the chemical bonding in the 2-block 

unit. The latter form of union is uncommon and all the structures presented in this text 

only deal with derivatives containing combinations of pairs of types A and B. 

3

1.1.1 The clathrate-like structure 

Clathrate-like systems are molecular or supramolecular arrangements in which an internal 

unit is encapsulated by an external core. In metal-oxide polynuclear clusters, it is a 

common phenomenon that has been discussed by experimentalists [24–26] and computational 

chemists [27–29]. A formulation for molecules that accomplish the requirements of 

a clathrate-like system was introduced in the way I-E, in which I and E are the internal 

and the external fragments. Keggin, Wells-Dawson and Lindqvist anions were also formulated 

as [XO 4 ] n− - M 12 O 36 - Keggin, [XO 4 ] n− - M 18 O 54 - Wells-Dawson or O 2− - M 6 O 18 

- Lindqvist 

1.1.2 Chemical elements taking part in POMs 

The addenda atoms ‘M’ have been identified as the most important entities in POMs. 

All the clusters included in this classification contain MO n units, so the characteristics 

of “M” deserve further discussion. Many ‘M’ elements are known to form octahedral 

coordination compounds with oxygen, but not so many can take part as MO 6 units of 

packed polynuclear metal-oxide aggregates. Therefore, structures of polyanions appear 

to be governed by the electrostatic charge (‘q’) and ionic radius (‘r’) principles of metal 

centers, that is, only selected values of the charge/radius ratio are observed in M n+ in 

combination with O 2− ligands, thus forming POMs. Few M’s are found in POM a structure 

since these physical limitations control the stability of the metal-oxide framework 

(see the values listed in Table 1.2 below). 

Table 1.2: List of common metal cations, M n+ , taking part in POM frameworks. We especially highlight 

W and Mo for being the most typical as addenda atoms 

Metal ion Octahedral radius (Å) Observed coordination numbers in POMs 

W 6+ 0.7 4, 6 

Mo 6+ 0.7 3 4, 6, 7 

V 5+ 0.68 4, 5, 6, 7 

Ta 5+ 0.78 6 

Nb 5+ 0.78 6 

The table contains early transition metal elements, from the left of the periodic table. 

In fact, there are other ions that have values of ‘q’ and ‘r’ with limits similar to those 

4

shown in Table 1.2. Apart from other transition metals, some p-block elements could 

be, at least in principle, good candidates for being included in MO 6 units as addenda. 

However, charge and radius are not the only considerations to rule these assemblages of 

metal-centerd units. Actually, an additional parameter to be considered, related to ‘M’, 

is the ability to form metal-oxygen pπ-dπ-bonds. This parameter affects the stability 

of these clusters, as well. It was observed long ago that, in octahedral MO 6 blocks, 

the metallic center is not in the middle of the polyhedron but somewhat displaced from 

the geometrical center towards one of the corners (see Figure 1.2). More precisely, it 

Fig. 1.2: Ball and stick represention of the α Keggin type cluster; the black balls represent tungsten and 

the red balls represent oxygen 

is displaced towards the corner which is not shared with another octahedron, so that 

the oxygen at this position usually forms M=O double bond with the metal. (see the 

cluster in Figures 2 and 3). Despite all of the above, after nearly two centuries of POM 

chemistry, almost all the elements of the periodic table have been incorporated into a 

polyoxometalate framework [1]. This accounts for the chemical variability of this field. 

1.1.3 Features of POMs 

Heteropoly- and isopolyanions are routinely prepared and isolated from both aqueous 

and non-aqueous solutions. The most common method of synthesis involves dissolving 

[MO n ] m− oxoanions which after acidification assemble to yield a packed molecular array 

of MO 6 units. For example, 

5

7(MoO 4 ) 2− + 8H + → [Mo 7 O 24 ] 6− + 4H 2 O (Eq = 1) 

(PO 4 ) 3− + 12(WO 4 ) 2− + 24H + → [PW 12 O 40 ] 3− + 12 H 2 O (Eq = 2) 

(WO 4 ) 2− + H 3 PO 4 (excess) + H + → [P 2 W 18 O 62 ] 6− + P 5 W 30 (Eq = 3) 

Care must be taken with pH conditions so that the reaction can be controlled. The 

sequence in which the reagents are added to the reaction media is also important. One of 

the most important steps in synthetic procedures of POMs are the isolation of crystals so 

that their features can be studied in greater depth. Clusters are precipitated or crystallized 

by adding countercations (alkali metals, organic cations like TBA, etc.) and subsequent 

separation. Usually the solid state structure of polyoxometalates is preserved in solution 

and an appropriate choice of the counterion allows the redissolution of a polyoxoanion in 

aqueous, organic or mixed aqueous/organic solvents. The structure of polyoxoanions is 

determined by single-crystal X-ray diffraction and the diamagnetic nature enables the use 

of multinuclear NMR, which is the most powerful technique for studying the structure in 

solutions. As far as preparation and storage conditions are concerned, it is worth noting 

that POMs are hydrolytically and thermally stable. 

1.2 Geometric Structures of representative types of 

Polyanions: Keggin, Lindqvist, Anderson-Evans 

and Wells-Dawson 

In 1933, Keggin left his name on the structure by correctly deducing its geometry based 

on powder X-ray diffraction patterns. The α isomer of the Keggin structure is shown in 

Figure 1.3. The structure has T d symmetry and it is composed of a central heteroatom 

tetrahedron (XO 4 ) surrounded by twelve peripheral or “addenda” atom octahedra (MO 6 ). 

The peripheral MO 6 units form four trimetallic clusters (triads). Four edge ‘O’ atoms hold 

the trimetallic cluster together, one linking to the central heteroatom (O i - ‘i’ for inner), 

and three bridging peripheral MO 6 octahedra (O e - ‘e’ for edge shared). The trimetallic 

clusters are linked to each other by corner-shared oxygen atoms (O c - ‘c’ for corner-shared), 

and each metal atom has a single terminal “oxo” ligand with double bonding character 

(O t - ‘t’ for terminal). Thus there are four non-degenerate oxygen species present in each 

6

Fig. 1.3: Ball/stick and polyhedral representation of the alpha isomer of the Keggin structure with 

different types of oxygen. Color codes: The blue polyhedra represent the tungsten and the red balls 

represent oxygen 

Keggin unit. The Keggin unit is usually anionic, and is balanced by cations in solid state. 

The cations may be protons (typically coordinated with water as [H 5 O 2 ] + or [H 9 O 4 ] + ), in 

which case the complex is acidic, and it is identified as a Heteropolyacid. Other typical 

charge-balancing cations generally used are alkali metals and ammonium derivatives. As 

mentioned above, the tetrahedral heteroatom at the center of the Keggin unit can be any 

of a wide array of elemental cations. The most commonly studied structures are those 

containing, As V , P V , Si IV , Ge IV as the heteroatom but other transition metals and non 

metals have been observed playing this role. Moreover, trigonal-pyramidal (e.g. AsO 3− 3 , 

Figure 1.4) or ditetrahedral (e.g. O 3 POPO 4− 3 ,Figure 1.5) hetero groups as additional 

building blocks allows further structural versatility. Furthermore, few types of addenda 

atoms have been observed in Keggin structures; typically, the addenda atoms are molybdenum 

or tungsten. Vanadium based structures are also reported, but its questionable 

whether they form 1:12 heteroatom:addenda complexes; it appears more likely that they 

form Keggin-like 1:13 or 1:14 complexes. Clusters with p-block elements (P, Si, Al, Ga and 

Ge), transition metal elements (Fe(II/III), Co(I/II), Ni(II/IV), Zn(II)), and even two H + 

have been synthesized. This position can be either tetrahedrally coordinated (as in Keggin 

and Wells-Dawson anions) or octahedrally coordinated (as in the Anderson structure). 

Figure 1.6 shows a [M 6 O 19 ] n− isopolyanion (A) and two heteropolyanions and Figures 1.7 

and 1.8 illustrates two different types of heteropolyanions. The [M 6 O 19 ] n− isopolyanion 

7

Fig. 1.4: Combined polyhedral/ball and stick representation of [Cu 3 Na 3 (H 2 O) 9 (α-As III W 9 O 33 ) 2 ] 9− 

Fig. 1.5: Combined polyhedral/ball and stick representation of {(O 3 POPO 3 )Mo 6 O 18 } 4− 

representative of the Lindqvist type structure [30]is characterized by the presence of one 

terminal M-O bond at each metal center and thus, they belong to the type-I category 

in Pope’s classification scheme. Each metal center is octahedrally coordinated and the 

structure consists of a compact assemblage of edgesharing octahedra, leading to an overall 

octahedral cluster, with full Oh symmetry. The pronounced distortion of each MO 6 unit 

and the three different oxygen coordination sites are shown in Figure 1.6. One can see 

8

Fig. 1.6: Ball and stick representation of the Lindqvist structure 

that the metals occupy equivalent octahedral sites, so that they make one short terminal 

M-O bond and a rather long M-O bond to the translocated high-coordinate oxygen 

site. This cluster is known as the Lindqvist type structure, e.g. [M 6 O 19 ] n− (n= 8 for 

M= Nb, Ta) and (n = 2 for M= Mo, W ). In Figure 1.7, the polyanion is based on an 

Fig. 1.7: Polyhedron representation of the Anderson structure 

arrangement of seven edge shared octahedra where the heteroatom “X” is surrounded 

by six-oxo ligands in a pseudo-octahedral symmetry and it occupies the central position. 

9

This planar structure was originally proposed by Anderson for the heptamolybdate anion, 

[Mo 7 O 24 ] 6− , but it was observed for the first time when Evans reported the structure of 

[TeMo 6 O 24 ] 6− , which was isostructural to that of the 6-molybdo-anion [IMo 6 O 24 ] 5− , It 

is generally know as ‘Anderson-Evans’ structure [31]. In Figure 1.8, the complete anion 

Fig. 1.8: Ball and stick representation of the Wells-Dawson structure 

consist of two identical ‘half-units’ related by a plane of symmetry perpendicular to the 

trigonal axis. The ‘half-units’ are linked together by six oxygen atoms situated in the 

plane of symmetry, so that these atoms are shared equally by the two halves. The two 

heteroatoms ‘X’ are tetrahedrally coordinated and surrounded by nine WO 6 octahedra 

linked together by edge sharing and corner sharing. This type of cluster is generally 

known as ‘Wells-Dawson structure’ [32]. 

1.3 Lacunary Species 

Although all polyoxoanions are ultimately decomposed to monomeric species in basic solution, 

controlling the pH can lead to the formation and isolation of ‘defect’ or ‘lacunary’ 

structures. These are best illustrated with the α isomers of the Keggin-type polyanion, 

the Keggin anion has five different rotational isomers known as ‘Baker-Figgis’(α,β,γ,δ,ɛ). 

10

β,γ,δ and ɛ are derived from the α-isomer, a cluster already mentioned above, by rotation 

of 60 ◦ of 1, 2, 3, and 4 different triads respectively. which can form [XM 11 O 39 ] n− and 

Fig. 1.9: Schematic representation of the formation of Keggin-type lacunary. Courtesy: Dr. Santiago C. 

Reinoso 

[XM 9 O 34 ] n− species by the ‘removal’ of one or three adjacent MO 6 octahedra respectively. 

An intermediate structure in which two adjacent octahedra have been removed has not 

been observed for the α and β isomers but observed only for the γ isomer; in the former 

two cases the structure would contain an MO 6 octahedron with three fac terminal oxygen 

atoms and is therefore expected to be quite reactive. Two kinds of the XM 9 anions can be 

formed, both having C 3v symmetry: A-type, in which three corner-shared octahedra have 

been lost, and B-type, in which three edge-shared octahedra have been lost. Neither of 

these sructures appears to be thermodynamically stable in solution, although both have 

been isolated as solids salts, and used to synthesize derivatives. In addition, both A- 

and B-type XM 9 structural units are recognizable in larger polyoxoanions. Examples are: 

11

[X 2 M 18 O 62 ] 6− , the D 3h Wells-Dawson structure formed by fusion of two A-XM 9 units; 

[As 2 W 21 O 69 ] 6− and [P 2 W 21 O 71 ] 6− , which contain two B- and A-type XW 9 units respectively 

separated by a ‘belt’ of three WO 6 octahedra; and [(NH 4 )As 4 W 40 O 140 ] 27− , containing 

four B-type AsW 9 units. The large tungstoarsenate(III) [As 6 W 65 O 217 (H 2 O) 7 ] 26− is the 

only example of a polyanion that contains both (α-AsW 9 O 33 ) and (β-AsW 9 O 33 ) isomers 

in the same structure [33]. Many of these larger structures can be further converted to 

lacunary species, e.g. X 2 M 18 (X= P, As) (‘Wells-Dawson structure’) yields X 2 M 17 , X 2 M 15 , 

and X 2 W 12 anions. 

Salts of the anions [AsW 9 O 33 ] 9− and [SbW 9 O 33 ] 9− were first reported by Rosenheim, and 

structurally confirmed by Krebs [34] and Tourné [35]. The anions appear to be stable at 

pH 7.5 to 9.0 and the potassium salts crystallize in a face centered cubic form isotypic 

with several lacunary Keggin salts mentioned earlier. This suggests an incomplete Keggin 

structure probably of B-type statistically oriented in the cubic cell. In contrast to the 

A-type 1:9 anions (Si, Ge, etc.), As III W 9 and Sb III W 9 do not react with tungstate to 

give As III W 11 and Sb III W 11 . However, solutions of the anions react with electrophiles to 

give complexes. 

These lacunary species derived from the Keggin type structure, are obtained from the 

three Baker-Figgis (α, β, γ) isomers by means of the elimination of a variable number of 

octahedra, so that a total of nine species are known whose structures are shown in above 

Figure 1.9 

In the case of phospho-tungstate system, the reaction patterns are similar to those of 

the silico-tungstates, but a series of remarkable differences exists, which can be visualized 

from the Figure 1.10 

The β-isomers are much more unstable and isomerize to the α-isomers, with the exception 

of the trivacant species A- β-[PW 9 O 34 ] 9− , which forms on acidifying solutions of 

tungstate and phosphate to pH around 9. When the reaction is carried out at 0 ◦ C, the 

A-α-isomer is obtained but it isomerizes to the A-β-isomer at room temperature. In addition, 

the dilacunary species γ-[PW 10 O 36 ] 7− is not synthesized directly, but by overnight 

refluxing of polyanion [P 2 W 5 O 23 ] 6− , overnight at pH = 7 and it is only isolated with 

12

Fig. 1.10: Schematic representation of the formation of Keggin- and Wells-Dawson type lacunary species 

in tungsto-phosphate system with respect to pH.Courtesy: Dr. Santiago C. Reinoso 

a cesium counterion. On the other hand, a series of heteropolyanions can be obtained 

which has no equivalent in silico-tungstate system. Thus, when the trivacant species 

A-α-[PW 9 O 34 ] 9− is acidified in excess of potassium counterion, instead of the Keggin 

ion formation, association of two trivacant species takes place by means of a bridging 

tungsten in the belt. If the pH is decreased different heteropolyanions are obtained, 

13

[P 2 W 19 O 68 (HO)] 14− , [P 2 W 20 O 70 (H 2 O) 2 ] 6− and [P 2 W 21 O 71 (HO) 3 ] 6− , which show one, two 

and three {WO(HO)} 4+ groups in the central belt, respectively. In addition, when a 

solution of tungstate is acidified until pH below 2 in the presence of an excess of phosphate, 

mixture of α and β-isomers of the Wells-Dawson [P 2 W 18 O 62 ] 6− heteropolyanion 

is obtained instead of the Keggin. The Wells-Dawson heteropolyanion shows a similar 

behaviour to that of the Keggin, since the basicity of its dissolution produces hydrolytic 

cleavage of the M-O bonds to give rise to monovacant [P 2 W 17 O 61 ] 10− lacunary species, 

only if the pH is in between 4 and 6, and to the trilacunary [P 2 W 15 O 56 ] 12− at pH around 

10. These trivacant species undergo irreversible processes of transformation to form the 

hexa lacunary species [P 2 W 12 O 48 ] 14− . Lacunary anions with more than one surface ‘vacancy’ 

may also be derivatized by cation complexation. Reaction of a stable, lacunary 

polyoxometalate with transition metal ions usually leads to a product with the unchanged 

heteropolyanion framework. Depending upon the coordination requirement and the size 

of a given transition metal ion, the geometry of the reaction product can therefore often 

be predicted. At the same time it must be pointed out that the mechanism of formation 

of polyoxometales is not well understood and commonly described as self assembly. 

Therefore, the synthesis of polyoxoanions with novel shapes and sizes is a very difficult 

task. But, according to Müller and Pope, POM structure are governed by two general 

principles. 

•Polyanions are generated by linking MO n polyhedra via corners and edges leading to 

different types of faces on the surfaces. 

•Each metal atom forms an MO n coordination polyhedron (most commonly an octahedron 

or a square pyramid) in which the metal atoms are displaced, as a result of M-Oπ 

bonding, towards the terminal polyhedral vertices forming the surface of the structure. 

Transition metal substituted polyoxometales can also be of interest owing to their magnetic 

properties. Structures which contain more than one paramagnetic transition metal 

ion in close proximity may exhibit exchange-coupled spins leading to large spin ground 

states [36, 37]. The polyoxometalate matrix may be considered as a diamagnetic host 

encapsulating and thereby isolating a magnetic cluster of transition metals. Polyoxometalate 

chemistry has received a great research interest in the area of oxidation catalysis 

14

and most publications in the field deal with the evaluation of the catalytic activity of 

polyoxoanion salts (oxidation catalysis) or the free acids (acid catalysis) [3–5, 38]. Polyoxoanions 

have been shown to activate small molecules (e.g. O 2 , H 2 O 2 ) which are highly 

desired oxidants in the chemical industries for the catalysis of organic reactions (e.g. epoxidation, 

hydroxylation). Currently polyoxoanions are being used as catalysts in different 

processes on an industrial scale worldwide. Substitution of one or more addenda atoms 

by redox-active transition metal ions (e.g. Fe 3+ , Ru 3+ ) allows to fine tune the catalytic 

activity of polyoxoanions [39]. 

The interactions of polyanions with enzymes and other biomolecules is also being studied 

and it allows for a better understanding of the antitumor/viral activities of this class 

of compounds [40–42]. It is also possible to graft organic groups to the surface of the 

polyoxoanions via incorporation of an organo-metal (PhSn) or an organo non-metal (e.g. 

RSi)[43] fragment in a lacunary polyoxometalate precursor. The monoorgano tin chemistry 

of polyoxometalates has been studied mainly by Pope and by few other groups. 

It is known that the size, shape and charge density of many polyoxoanions are of interest 

for pharmaceutical applications. However, the mechanism of action of many polyoxoanions 

is not selective towards a specific target. In order to improve selectivity it appears 

desirable slightly to modify a given polyoxoanion core structure . However, such attempts 

frequently result in a different polyoxoanion framework. Therefore the most straightforward 

and promising approach towards systematic derivatization of polyoxoanions involves 

attachment of organic groups to the surface of the metal-oxo framework. In order to be 

attractive for pharmaceutical applications, the functionalized polyoxoanions should be 

water-soluble and fairly stable at physiological pH. 

To date the number of water-soluble polyoxoanions with tightly bound organic functionalities 

is rather small. Pope and co-workers [44–47] were the first to study the interaction 

of monoorganotin groups (e.g. n-C 4 H 9 Sn 3+ , C 6 H 5 Sn 3+ ) and polyoxoanions. They reacted 

different organotin halide precursors (e.g. n-C 4 H 9 SnCl 3 , C 6 H 5 SnCl 3 ) with a large number 

of lacunary heteropolytungstates in aqueous solution and they were able to identify 

novel (mostly dimeric) polyoxoanion structures. Single-crystal X-ray diffraction studies 

revealed that these compounds contain tightly anchored organotin fragments. The com- 

15

Fig. 1.11: Monomeric (left) and dimeric species (right) of monoorganotin containing polyoxotungstates. 

pounds were also studied in solution by multinuclear NMR spectroscopy. This technique 

is also very valuable in the evaluation of the stability of polyoxoanions at physiological 

pH and low concentration for medicinal applications. Liu and coworkers [48–52] have also 

synthesized some monoorganotin substituted polyoxotungstates. They introduced ester 

functionalities to the organotin fragments and tested the biological (antitumor) activity 

of their products. Most recently, the groups of Pope and Hasenknopf showed independently 

that monoorganotin containing polyanions can be further derivatized by peptide 

or ester functions [53–55]. Haiduc et al. also reported on monoorganotin derivatives of 

polyoxotungstates [56]. However, the proposed structures of Liu and Haiduc need to be 

confirmed by X-ray diffraction. 

Interestingly, there were no reports on diorganotin substituted polyoxotungstates. Such 

species could allow for more flexibility for the interaction with and binding to other organic 

compounds and biomolecules. Therefore we investigated the interaction of di-organotin 

groups with the entire arsenal of lacunary polyoxotungstates. 

Introduction of organic groups into the POM framework could greatly increase the number 

of compounds available for screening, together with a potential modulation of essential 

features such as stability, bioavailability, recognition, etc [57]. While there is a signifi- 

16

cant amount of work on hybrid polyoxometales,[58–60] there have been only few reports 

of the reactivity of the side chain of such functionalized POMs [61–63]. Many of these 

organically derivatized POMs are unstable in water. Starting from hydrolytically more 

stable cyclopentadienyltitanium substituted POMs, [64, 65] Keana reported the preparation 

and reactivity of derivatives with various functional groups. [66, 67] We decided to 

re-examine hetropolytungstates with an alkyltin group, because these compounds might 

have promising antitumor activities [68]. It is important to have access to a wide variety 

of organic groups on the POM to meet specific requirements in biological applications. 

Different groups like -NH 2 for instance will enable the POM to cross a membrane or to 

reach a specific receptor depending on their precise nature. 

17

Chapter 2 

Experimental 

2.0.1 Reagents 

All chemicals were purchased from well known chemical companies, and used as received: 

(CH 3 ) 2 SnCl 2 and InCl 3 (anhydrous)was purchased from Fluka Chemie, TiOSO 4 was purchased 

from E.Merck AG, C 6 H 5 SnCl 3 was purchased from Aldrich Chem.Co. D 2 O was 

purchased from AppliChem. CdCl 2·H 2 O, was purchased from Riedel-de haën.The purity 

of the dimethyl tin was 95% and that of monophenyl tin was 98%. 

2.1 Instrumentation 

2.1.1 Infrared spectroscopy 

Infrared spectra with 4 cm −1 resolution were recorded on a Nicolet Avatar 370 FT-IR 

spectrophotometer as KBr pellet samples. The following abbreviation was used to assign 

the peak intensities: w = weak; m = medium; s = strong; vs = very strong; b = broad; 

sh = shoulder. 

2.1.2 Single crystal X-ray diffraction 

X-ray diffraction data collection was carried out on a Bruker D8 SMART APEX CCD 

single crystal diffractometer equipped with a sealed Mo anode tube.The SHELX software 

package was used in order to solve and refine the structures. Direct method solutions 

18

located the heaviest atoms and remaining atoms were found in subsequent Fourier difference 

syntheses. Refinements were full-matrix least-squares on F 2 for structures having not 

more than 1200 parameters, and were block-diagonal least-squares on F 2 for structures 

having more than 1200 parameters. Routine Lorentz and polarization corrections were 

applied and absorption corrections were performed using the SADABS program. a R = 

∑ ||Fo |-|F c ||/ ∑ |F o |. b R w = [ ∑ w(F 2 o-F 2 c) 2 / ∑ w(F 2 o) 2 ] 1/2 

2.1.3 Multinuclear magnetic resonance spectroscopy 

NMR spectra were recorded on a JEOL 400 ECX spectrometer operating at 9.39 T (400 

MHz for proton) magnetic field. The resonance frequencies were 161.834 MHz for 31 P, 

149.081 MHz for 119 Sn and 16.656 MHz for 183 W. Chemical shifts are given with respect 

to external standard 85% H 3 PO 4 for 31 P, (C 2 H 5 ) 4 Sn for 119 Sn, 2 M Na 2 WO 4 for 183 W. All 

aqueous 183 W NMR spectra were collected on highly concentrated solution. 

2.1.4 Cyclic voltametry 

All cyclic voltammogramms (CV) were recorded on a EG & G 273 A voltameter driven by 

a PC with the M270 software. Potentials are coated against a saturated calomel electrode 

(SCE). The counter electrode was a platinum gauze of large surface area. All experiments 

were performed at room temperature. 

2.1.5 Elemental analyses and thermogravimetric analysis 

All elemental analyses were performed by Kanti Labs Ltd. in Missisunga, Canada. Thermogravimetric 

analysis (TGA): Water contents were determined using a TGA Thermalgravimetric 

Analyzer with 15-20 mg samples in 100 µL alumina pans, under a 100 mL 

min −1 N 2 flow and with heating rates of 5 ◦ C min −1 . 

19

2.2 Preparation of starting materials 

2.2.1 Synthesis of Na 9 [AsW 9 O 33 ]·27H 2 O 

To a hot (∼95 ◦ C) solution of 110g of Na 2 WO 4·2H 2 O in 117 mL of distilled water, 3.67 

g of As 2 O 3 were added. Then 27.7 mL concentrated HCl were added dropwise with in 

2 minutes with continuous stirring for a period of 10 minutes. The solution was cooled 

for a while and than filtered into a beaker and covered with parafilm. The formation of 

crystals starts when the solution cools in the period of time. The filtrate was left in an 

open beaker until the solution reached the mark of crystals. The crystals were collected 

in a bruchner funnel and dried at ∼50 ◦ C in an air oven overnight. The final compound 

was characterized by FTIR spectroscopy and compared to the reported spectrum [69]. 

2.2.2 Synthesis of Na 9 [SbW 9 O 33 ]·27H 2 O 

Solution A : 1.96 g of Sb 2 O 3 were dissolved in 10 mL conc. HCl (may or may not 

dissolve completely). Solution B : 40g of Na 2 WO 4·2H 2 O were dissolved in 80 mL of 

distilled water (∼90 ◦ C). Solution A was transferred into the beaker containing Solution 

B. including the non dissolved Sb 2 O 3 drop wise and then, the whole reaction mixture was 

refluxed for approximately an hour. The solution was cooled and filtered, crystals start 

forming immediately. Solution was left open until the it reached the level of crystals. The 

final compound was characterized by FTIR spectroscopy and compared to the reported 

spectrum [70]. 

2.2.3 Synthesis of K 14 [As 2 W 19 O 67·(H 2 O)] 

To a solution of 94g (285 mmol) of Na 2 WO 4·2H 2 O in 250 mL of distilled water. 4.45g 

(22.5 mmol) of As 2 O 3 were added subsequently. The solution was stirred for few minutes 

and pH was adjusted to 6.3 by addition of 12 M HCl (37%).The solution was heated to 

∼80 ◦ C for 10 mins, and after cooling 35g (45 mmol) of KCl was added to the solution at 

room temperature. The solution was stirred again for 15 mins and the formed precipitate 

was filtered off and dried at ∼80 ◦ C in an air oven overnight. It was characterized by 

FTIR spectroscopy and compared to the reported spectrum [71]. 

20

2.2.4 Synthesis of A & B Na 8 [HAsW 9 O 34 ]·11H 2 O (A & B-Type 

AsW 9 O 34 ) 

30 g of Na 2 WO 4·2H 2 O and 2.3 g of As 2 O 5 were dissolved in 40 mL of distilled water with 

stirring. Glacial CH 3 COOH was added drop wise until the pH changed to 8.1 or 8.3 the 

solution turned milky on addition of CH 3 COOH but after stirring for a period of 30 min 

a heavy white precipitate was formed. The precipitate was filtered on a frit and air dried. 

The product obtained is A-AsW 9 O 34 . If the above product is kept in the oven for a period 

of 2hrs at ∼140 ◦ C it isomerizes to give B-AsW 9 O 34 . These synthesis was done with slight 

modification to the published method. They were characterized by FTIR spectroscopy 

and compared to the A & B reported spectrum [72]. 

2.2.5 Synthesis of A-Na 9 [PW 9 O 34 ]·7H 2 O 

120 g (0.36 mol) of Na 2 WO 4·2H 2 O were dissolved in 150 g of distilled water. H 3 PO 4 (85%) 

was added dropwise with stirring. After the completion of addition, the pH of the solution 

was measured to be 8.9. Glacial CH 3 COOH was added dropwise with vigorous stirring. 

Large quantities of white precipitate were formed during the addition. The final pH of 

the solution was 7.8. The solution was stirred at least for an hour and the precipitate 

was collected on a medium frit. Heating of the crude product at ∼120 ◦ C induces a solid 

state isomerization from A-type to B-type. These compounds were characterized by FTIR 

spectroscopy and 31 P-NMR spectroscopy and compared to the FTIR reported spectrum 

[73]. 

2.2.6 Synthesis of Cs 6 [P 2 W 5 O 23 ]·H 2 O 

60 g ( 0.24 mol) of H 2 WO 4 was slurried with 200 g of water. Approximately 110 mL 

of a 50% aqueous CsOH solution was added drop wise with vigorous stirring. The turbid 

solution was filtered through a cake of 10 g celite and to the clear colorless filtrate 

H 3 PO 4 (85%) was added drop wise while stirring to adjust the pH to 7.0. The solution 

was again stirred for an hour and filtered again. The filtrate was cooled to ∼0 ◦ C in 

refrigerator for 24 hours and the white crystalline solid was formed which was identified 

21

as Cs 6 [P 2 W 5 O 23 ]·7H 2 O by FTIR spectroscopy [73]. 

2.2.7 Synthesis of Cs 7 [PW 10 O 36 ]·H 2 O 

75 g of Cs 6 [P 2 W 5 O 23 ]·H 2 O synthesized by the above procedure was dissolved in 150 g of 

water and the resulting was refluxed for 24 hour. The solution was filtered hot through a 

medium frit to obtain the crude product Cs 7 [PW 10 O 36 ]·H 2 O. The filtrate was cooled for 

48 hr at ∼0 ◦ C, and filtered to recover the unconverted Cs 6 [P 2 W 5 O 23 ]·H 2 O, which was 

again used to synthesize Cs 7 [PW 10 O 36 ]·H 2 O. The product was characterized by FTIR 

spectroscopy [73]. 

2.2.8 Synthesis of Na 20 [P 6 W 18 O 79 ]·37.5H 2 O 

To a solution of 50 g of Na 2 WO 4·2H 2 O in 50 mL of distilled water. 3.5 mL of (85%) 

H 3 PO 4 was added to the solution subsequently. This resulting solution was boiled until 

the final volume reached 50 mL. The solution was cooled and on cooling white crystalline 

precipitate was formed, which was recrystallized from water to get pure crystalline material. 

It was than characterized by FTIR and 31 P-NMR spectroscopies and was compared 

with the published data [74]. 

2.2.9 Synthesis of K 12 [H 2 P 2 W 12 O 48 ]·24H 2 O 

83 g of K 6 [P 2 W 18 O 62 ]·X H 2 O was dissolved in 300 mL of distilled water, and than a 

solution of 48.4 g (0.4 mol) of tris base in 200 mL water was added. The solution was left 

at room temperature for 30 minutes and then 80 g of solid KCl was added. After complete 

dissolution, a solution of 55.3 g (0.4 mol) of K 2 CO 3 in 200 mL of water was added. The 

resulting mixture was stirred for 15 minutes and a white precipitate appeared in due 

course of stirring. It was collected on a coarse sintered frit, dried under suction for 12 

hours and washed couple of times with ethanol. The precipitate was then air dried for 3 

days. It was characterized by FTIR and 31 P-NMR spectroscopies and was compared with 

the published data [75]. 

22

2.2.10 Synthesis of K 16 Li 2 [H 6 P 4 W 24 O 94 ]·33H 2 O 

8 g of K 12 [α-H 2 P 2 W 12 O 48 ]·24H 2 O was dissolved in 250 mL of 1 M aqueous solution of LiCl 

acidified by 0.7 mL of CH 3 COOH. The solution was left for 4 hours at room temperature 

and then 50 mL of saturated KCl solution was added. The formed white precipitate was 

filtered off and washed with KCl solution and twice with ethanol. The precipitate was air 

dried overnight and It was than characterized by FTIR and 31 P-NMR spectroscopies and 

was compared with the published data [76]. 

2.2.11 Synthesis of K 28 Li 5 [H 7 P 8 W 48 O 184 ]·92H 2 O 

28 g of K 12 H 2 P 2 W 12 O 48·24H 2 O was dissolved in 1 litre of a mixture of LiCl (0.5 mol), 

LiOAc (0.5 mol) and CH 3 COOH (0.5 mol) in water. The solution was left open instead of 

being closed as published earlier. After 1 day white crystalline needles started appearing. 

The solution was left for a week for further crystallization. The crystalline material was 

filtered in a frit and kept for air drying. It was than characterized by FTIR and 31 P-NMR 

spectroscopies and was compared with the published data [76]. 

2.2.12 Synthesis of Na 27 [NaAs 4 W 40 O 140 ]·60H 2 O 

132 g (0.4 mol) of Na 2 WO 4·2H 2 O and 5.2 g (40 mmol) Na 2 AsO 3 were dissolved in 200 mL 

of distilled water at ∼80 ◦ C. 6 M HCl was added slowly with vigorous stirring until the 

final pH reached to 4.0. The solution was cooled and kept in refrigerator at ∼80 ◦ C , the 

solid crystalline product crystallizes slowly. One day is required for complete deposition. 

The white solid is collected on a filter paper and air dried. The synthesized product was 

characterized using FTIR spectroscopy and was compared with the published data [77]. 

2.2.13 Synthesis of K 8 [γ-SiW 10 O 36 ]·20H 2 O 

To prepare γ-SiW 10 , at first β 2 -SiW 11 was prepared as follows 5.5 g (25 mMol)of Na 2 SiO 3·5H 2 O 

was dissolved in 50 mL of distilled water. (solution A) 91 g (0.25 mMol)of Na 2 WO 4·2H 2 O 

was dissolved in 150 mL of H 2 O in 1 liter beaker.(Solution B) 82.5 mL of 4 M HCl was 

added in 1 mL portion over 10 min. Solution A was added to solution B and the pH 

23

was adjusted between 5-6 by addition of 4 M HCl for 100 min.( 1hr, 40 min) Later 4.45 

g solid KCl was added to the resulting solution and stirred for 15 min to obtain solid 

white precipitate. This uncharacterized product is K salt of βSiW 11 . In order to obtain 

γ-SiW 10 , 15 g of K salt of βSiW 11 was dissolved in 150 mL of distilled water. Insoluble 

impurity was removed by filtering on a frit containing celite. The pH of the solution was 

adjusted to 9.1 with 2 M aqueous solution of K 2 CO 3 solution. The pH of this solution 

was kept at this value for exactly 16 minutes. 85 gm of KCl was added to it and stirred 

for 10 minutes. The pH was still maintained at 9.1. by adding 2 M aqueous solution of 

K 2 CO 3 solution. 40 g of solid KCl was added to obatin K-salt of γ-SiW 10 . The precipitate 

was dried overnight at 50 degree in hot air oven. It was characterized using FTIR 

spectroscopy and was compared with the published data [78]. 

2.2.14 Synthesis of K 7 [PW 11 O 39 ]·14H 2 O 

To a solution of 181.5 g Na 2 WO 4·2H 2 O in 300 mL H 2 O was slowly added 50 mL of 1M 

H 3 P0 4 and 88 mL glacial acetic acid. This solution was refluxed for 1 hour and then 

cooled to room temperature. Addition of 60 g solid KCl leads to white precipitate which 

was collected after 10 minutes and air dried. The solid product was characterized using 

FTIR spectroscopy and was compared with the published data [79]. 

2.2.15 Synthesis of K 14 [P 2 W 19 O 69 (H 2 O)]·24H 2 O 

The precursor was synthesized from the mixtures of K 7 PW 11 O 39 (aq) and Na 8 [HPW 9 O 34 ] 

(aq). A solution of Na 8 [HPW 9 O 34 ] (aq) (10.65 g , 3.75 mmol) was added to K 7 PW 11 O 39 

(aq) (4.0 g 1.25 mmol), the pH reduced to 6-6.5 and the mixture was stirred and heated 

to 50 C. Solid KCl was added until a fine crystalline precipitate appeared . Further 

solid KCl about 3-4 g was then added. A white crystalline powder separated. Stirring 

was maintained until room temperature was reached. The product was then filtered off 

and washed with chilled water (10 mL). The solid product was characterized using FTIR 

spectroscopy and was compared with the published data [80]. 

24

Part-I 

Dimethyltin containing POMs

Chapter 3 

Results 

3.1 The hybrid organic-inorganic 2-D material 

(CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )]·5H 2 O) ∞ 

(X = As III , Sb III ) and its solution properties 

3.1.1 Experimental 

The lacunary precursors Na 9 [α-AsW 9 O 33 ] and Na 9 [α-SbW 9 O 33 ] were synthesized according 

to published procedures and their purity was confirmed by infrared spectroscopy 

[69, 70]. All other reagents were used as purchased without further purification. 

Syntheses 

0.58g (2.64 mmols) Sn(CH 3 ) 2 Cl 2 was dissolved in 40 mL distilled H 2 O followed by addition 

of 2.00 g (0.80 mmol) Na 9 [α-AsW 9 O 33 ] This solution at pH 3.0 was heated to ∼80 ◦ C for 1 

h and then cooled to room temperature and filtered. A few drops of 0.1 M CsCl were added 

and then the solution was allowed to evaporate in an open beaker at room temperature. 

After 1-2 days a white crystalline product started to appear. Evaporation was allowed to 

continue until the solvent level had approached the solid product, which was filtered off 

and air-dried. A total of 1.9 g (yield 76%) of crystalline product was obtained. Elemental 

analysis calculated. (found) for (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-AsW 9 O 33 )]·5H 2 O) ∞ 

(CsNa-1)(MW = 3107.0): Cs 4.3 (4.0), Na 3.0 (2.8), Sn 11.5 (10.9), As 2.4 (2.1), W 53.3 

26

(54.0)% FTIR spectra for (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-AsW 9 O 33 )]·5H 2 O) ∞ (CsNa- 

1)(KBr disk): 954, 909, 870, 829, 760, 727, 688, 518, 476, 430 cm −1 

(CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-SbW 9 O 33 )]·5H 2 O) ∞ (CsNa-2) The synthesis was iden- 

Fig. 3.1: FTIR spectra of compound CsNa-1(red) and Na 9 [α-AsW 9 O 33 ] (blue) 

tical to that of CsNa-1, with the exception that 2.0 g (0.80 mmol) Na 9 [α-SbW 9 O 33 ] was 

used instead of Na 9 [α-AsW 9 O 33 ]. In this case a total of 2.0 g (yield 79%) of crystalline 

product was obtained. Elemental analysis calcd. (found) for (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β- 

SbW 9 O 33 )]·5H 2 O) ∞ (MW = 3153.8): Cs 4.2 (3.9), Na 2.9 (2.8), Sn 11.3 (11.2), Sb 3.9 

(3.8), W 52.5 (53.4)%. FTIR spectra for (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 ( β-SbW 9 O 33 )]·5H 2 O) ∞ 

(KBr disk): 951, 865, 820, 747, 677, 520, 473, 457, 422 cm −1 . All elemental analyses were 

performed by Kanti Labs Ltd. in Mississauga, Canada. The FTIR spectra were recorded 

on a Nicolet Avatar FTIR spectrophotometer in a KBr pellet. 

X-ray Crystallography 

Crystal data and structure refinement details for (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-AsW 9 O 33 )] 

·5H 2 O) ∞ CsNa-1 and (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-SbW 9 O 33 )]·5H 2 O) ∞ CsNa-2 are 

summarized in Table 3.1. The respective crystals were mounted on a glass fiber for indexing 

and intensity data collection at 173 K on a Bruker D8 SMART APEX CCD single- 

27

Fig. 3.2: FTIR spectra of compound CsNa-2(red) and Na 9 [α-SbW 9 O 33 ](blue) 

crystal diffractometer using Mo K α radiation (λ = 0.71073 Å). Direct methods were used 

to solve the structure and to locate the heavy atoms (SHELXS97). Then the remaining 

atoms were found from successive difference maps (SHELXL97). Routine Lorentz and 

polarization corrections were applied and an absorption correction was performed using 

the SADABS program.[81] Crystallographic data are summarized in Table 3.1. 

Solution NMR 

Solution NMR appears to be the most elegant technique to prove or disprove the existence 

of 1 and 2 in solution. It is well known that NMR of the addenda atoms 

(in this case tungsten) is the most sensitive analytical tool to obtain structural information 

of polyoxoanions in solution. The polymeric compounds CsNa-1 and CsNa- 

2 are ideal for a multinuclear NMR study, because they contain several NMR-active, 

spin 1/2 nuclei and they are diamagnetic. Therefore we performed 183 W-, 119 Sn-, 1 H- 

and 13 C-NMR studies on (a) freshly synthesized solutions of CsNa-1 and CsNa-2 (see 

Experimental Section) and (b) solid CsNa-1 and CsNa-2 redissolved in water. Interestingly 

we obtained exactly the same results in both cases. NMR (D 2 O, 293 K) for 

28

Table 3.1: Crystal Data and Structure Refinement for compounds CsNa-1 and CsNa-2 

formula AsC 6 CsH 36 Na 4 O 43 Sn 3 W 9 (1) C 6 CsH 36 Na 4 O 43 SbSn 3 W 9 (2) 

fw (g/mol) 3107 3153.8 

crystal color colorless colorless 

crystal system orthorhombic orthorhombic 

crystal size (mm 3 ) 0.10 × 0.06 × 0.02 0.11 × 0.06 × 0.04 

space group (No.) P na2 1 (33) P na2 1 (33) 

unit cell dim. 

a (Å) 26.118(2) 26.118(2) 

b (Å) 16.064(1) 16.064(1) 

c (Å) 13.776(1) 13.776(1) 

vol (Å 3 ) 5779.4(7) 5779.4(7) 

Z 1 1 

dcalc (Mg m −3 ) 3.561 3.672 

abs. coeff. (mm −1 ) 20.548 20.595 

Reflections (unique) 14373 14370 

Reflections (obs.) 11413 12214 

a 

R (F o) 0.068 0.052 

b 

R w(F o) 0.1401 0.1078 

diff. peak (eÅ 3 ) 5.248 2.985 

diff. hole (eÅ 3 ) -5.107 -3.762 

R = ∑ ||F o |-|F c ||/ ∑ |F o |. b R w = [ ∑ w(F 2 o-F 2 c) 2 / ∑ w(F 2 o) 2 ] 1/2 

(CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-AsW 9 O 33 )]·5H 2 O) 183 ∞ W: (relative intensities in parenthesis) 

-130.5(2), -135.2(1), -138.1(2), -142.5(2), -146.2(2) ppm; 119 Sn: -175.9(1), -200.0(2) 

ppm; 13 C: 8.5 ppm; 1 H: 0.7 ppm. NMR (D 2 O, 293 K) for (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β- 

SbW 9 O 33 )]·5H 2 O) : 183 W: (relative intensities in parenthesis) -108.1(2), -117.4(1), -120.1(2), 

-127.1(2), -134.7(2) ppm; 119 Sn: -164.6(1), -205.2(2) ppm; 13 C: 8.7 ppm; 1 H: 0.7 ppm. All 

NMR spectra were recorded with freshly synthesized, concentrated solutions of CsNa-1 

and CsNa-2 on a JEOL Eclipse 400 instrument. The 183 W-NMR measurements were performed 

at 16.656 MHz in 10 mm tubes and the 119 Sn, 13 C, and 1 H spectra were recorded 

in 5 mm tubes at 149.081, 100.525 and 399.782 MHz, respectively. The chemical shifts 

for unbound dimethyltin dichloride at pH 3 are at -243.7 ppm ( 119 Sn), 12.2 ppm ( 13 C) 

and 0.84 ppm ( 1 H), respectively. 

29

Fig. 3.3: W 183 NMR spectra of (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 ( β-XW 9 O 33 )]·5H 2 O) ([X = As (top)CsNa- 

1, Sb (bottom)CsNa-2] 

3.1.2 Results and discussion 

The novel and isostructural polyoxoanion-based 2-D materials (CsNa 4 [Sn(CH 3 ) 2 } 3 O(H 2 O) 4 

(β-XW 9 O 33 )]·5H 2 O) (X = As, CsNa-1; Sb, CsNa-2), see Figures 3.5. The structure of 

CsNa-1 and CsNa-2 is best described as a polymeric network composed of monopolyanionic 

building blocks ({Sn(CH 3 ) 2 (H 2 O) 2 } 3 (β-XW 9 O 33 )) (X = As, Sb) that are linked via 

Sn-O-(W’) bridges. This leads to a 2-D surface which is not planar, but could perhaps be 

described as a shelf with a zig-zag backbone where the individual levels are decorated by 

methyl groups. Clearly, the solid state structure is governed by the organic functionalities. 

Compounds CsNa-1 and CsNa-2 are isostructural, which means that the different sizes 

of the As and Sb heteroatoms with their associated lone pairs have no significant effect 

on the solid state structures. The three organo-tin groups attached to each monomeric 

unit of CsNa-1 and CsNa-2 contain tin centers that are octahedrally coordinated by 

two oxo groups, two methyl groups and two water molecules, respectively. Furthermore 

the two methyl groups on each tin atom are positioned trans to each other. However, 

only two organotin groups are structurally equivalent and different from the third. The 

molecular formulae and charges of CsNa-1 and CsNa-2 are supported by bond valence 

30

Fig. 3.4: Sn 119 NMR spectra of (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 ( β-XW 9 O 33 )]·5H 2 O) [X = As (top)CsNa- 

1, Sb(bottom)CsNa-2] 

calculations, which indicate that all terminal oxygen atoms bound to the tin atoms are 

diprotonated.[82] Close inspection of CsNa-1 and CsNa-2 indicates that the C-Sn-C 

bond angles are significantly smaller than ∼180 ◦ C indicating that the interior methyl 

groups experience still some degree of repulsion (see Figure 3.6). The C-Sn-C bond angles 

of the two equivalent organotin groups are very similar for 1a (149(1), 152(1)) and 

CsNa-2 (150(1), 151(1) ◦ ). However, the C-Sn-C bond angle of the unique organotin 

unit is distinctly larger in polyanion CsNa-1 (166(1) ◦ ) than in CsNa-2 (162(1) ◦ ). This 

seems to reflect (a) the smaller size of the As III atom compared to Sb III , (b) the shorter 

As III -O bond lengths compared to Sb III and (c) the smaller size of the As III lone pair 

compared to Sb III . It is known that the alpha to beta isomerization of [α-AsW 9 O 33 ] 9− 

and [α-SbW 9 O 33 ] 9− is facilitated in acidic, aqueous medium [69, 83]. This is in complete 

agreement with the synthetic conditions for CsNa-1 and CsNa-2, which were isolated 

at pH 3. The (β-AsW 9 O 33 ) fragment has so far only been observed in two different polyoxoanion 

structures [33, 83]. The large tungstoarsenate(III) [As 6 W 65 O 217 (H 2 O) 7 ] 26− is the 

only example of a polyanion that contains both isomers, (α-AsW 9 O 33 ) and (β-AsW 9 O 33 ), 

31

Fig. 3.5: Left: combined polyhedral and ball/stick representation of the 2-D solid state structure of 

(CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )]·5H 2 O) ∞ (X = As, CsNa-1; Sb, CsNa-2). The WO 6 octahedra 

are purple and the balls represent tin (green), arsenic/antimony (blue), oxygen (red) and carbon 

(yellow). Hydrogen atoms are omitted for clarity (left),Right: Side view of the 2-D solid state structure 

of (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )]·5H 2 O) ∞ (X = As, CsNa-1; Sb, CsNa-2). 

in the same structure [33]. The fact that no cations are involved in the exclusively covalent 

2-D network of CsNa-1 and CsNa-2 requires it to possess a negative charge. Indeed the 

appropriate number of cations (1 Cs, 4 Na) for each polyanionic unit was found by X-ray 

diffraction and elemental analysis. Therefore CsNa-1 and CsNa-2 are best described as 

polymeric polyanion salts. This view is further supported by our observation that CsNa-1 

and CsNa-2 are water-soluble upon heating. Clearly, in solution the polymeric structure 

of CsNa-1 and CsNa-2 has to decompose and we identified the likely sites: the very 

long Sn-O(W’) bonds in CsNa-1 (2.414 - 2.656 Å) and CsNa-2 (2.427 - 2.633 Å). The 

question arises in which form CsNa-1 and CsNa-2 are present in solution: oligomeric 

or monomeric. The latter option requires the existence of the hypothetical, monomeric 

polyanion [{Sn(CH 3 ) 2 (H 2 O) 2 } 3 (β-XW 9 O 33 )] 3− (X = As III 1, Sb III 2). Polyanion 1 consists 

of a (β-AsW 9 O 33 ) fragment which is stabilized by three dimethyltin fragments and 

polyanion 2 represents its antimony derivative (see Figures 3.6). 

The three dimethyltin groups of 1 and 2 are grafted onto the polyanion via two Sn- 

32

Fig. 3.6: Left:Ball and stick representation of [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )] 3− (X = As,1; Sb,2.(A) 

The balls represent tungsten (black), tin (green), arsenic/antimony (blue), oxygen (red), carbon (yellow) 

and hydrogen (small black); Right:Combined polyhedral/ball and stick representation of the 

[{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )] 3− (X = As, 1; Sb, 2).(B) The WO 6 octahedra are red and the color 

codes of balls are same as above 

O(W) bonds each on the side of the hetero atom lone pair. Tungsten-183 NMR resulted 

in five peaks (intensity ratios 2:1:2:2:2) for 1a at -130.5, -135.2, -138.1, -142.5 and -146.2 

ppm and for 1b at -108.1, -117.4, -120.1, -127.1 and -134.7 ppm (see Figure 3.3). The 

latter spectrum shows an additional, very small peak at -124.6 ppm for which we do not 

yet have a good explanation. We also performed 119 Sn-NMR and observed two peaks with 

an intensity ratio of 1:2 at -175.9, -200.0 ppm CsNa-1 and -164.6, -205.2 ppm CsNa-2 

(see Figure 3.4). Interestingly both signals for CsNa-1 are somewhat broader than those 

for CsNa-2. The 13 C-NMR measurements resulted in one peak for CsNa-1 at 8.5 ppm 

and for CsNa-2 at 8.7 ppm. As expected 1 H-NMR resulted also in one peak at 0.7 

ppm for CsNa-1 and CsNa-2. All of these results indicate that in solution a species 

with C s symmetry is present. This proofs unequivocally the existence of the discrete, 

monomeric polyanions 1 and 2 in solution. Furthermore, the NMR spectra for CsNa-1 

and CsNa-2 do not change even after several months. Apparently the dimethyltin groups 

are tightly bound to the tungsten-oxo fragment. The monomeric polyoxoanions 1 and 2 

are synthesized by heating an aqueous solution containing dimethyltin dichloride and 

Na 9 [α-XW 9 O 33 ] (X = As III , Sb III ) in the appropriate stoichiometric ratio (3:1) in aqueous, 

acidic medium. From this solution the polymeric materials CsNa-1 and CsNa-2 are 

33

formed upon crystallization and both products can be isolated in good yield. Interestingly 

formation of 1 and 2 is accompanied by the isomerization (α-XW 9 O 33 ) → (β-XW 9 O 33 )(X 

= As, Sb). Most likely steric interactions of the methyl groups do not allow formation of 

the hypothetical trisubstituted alpha derivative [{Sn(CH 3 ) 2 (H 2 O) 2 } 3 (α-XW 9 O 33 )] 3− (X= 

As III , Sb III ). More precisely, the three ‘internal’ methyl groups of three different tin centers 

would come very close to each other if they were to be grafted on a (α-AsW 9 O 33 ) or 

(α-SbW 9 O 33 ) fragment. Furthermore the lone pair of electrons on the heteroatom may 

exhibit a repulsive effect on the internal methyl groups. Rotation of one W 3 O 13 by ∼60 

◦ C allows results in the beta-isomer and now all three dimethyltin units can be bound 

resulting in a stable structure. Almost certainly the terminal oxygens of all tin atoms are 

diprotonated. The presence of labile water ligands explains the tendency of 1 and 2 to 

polymerize in the solid state. 

3.1.3 Conclusions 

The diorganotin fragments can be incorporated in polyoxotungstates. Polyanions 1 and 

2 represent (a) novel examples of hybrid organic-inorganic polyoxoanions, (b) the first 

examples of diorganotin-substituted polyoxoanions, (c) the first monomeric organotin 

derivatives of lone pair containing polyoxoanions and (d) the first organotin derivatives of 

[β-AsW 9 O 33 ] 9− and [β-SbW 9 O 33 ] 9− . The compounds presented here are rare examples of 

discrete polyoxoanions which polymerize upon crystallization leading to a 2-D structure 

with inorganic and organic surface regions. 

34

3.2 The tetrakis-dimethyltin containing 

tungstophosphate ({Sn(CH 3 ) 2 } 4 {H 2 P 4 W 24 O 92 } 2 ) 28− 

evidence for lacunary Preyssler ion 


Synthesis 

K 17 Li 11 [{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ]·51H 2 O (KLi-3). Polyanion 3 was synthesized by 

interaction of 0.072 g (0.30 mmol) (CH 3 ) 2 SnCl 2 with 0.728 g (0.10 mmol) K 16 Li 2 [H 6 P 4 W 24 O 94 ] 

in 20 mL LiOAc buffer at pH 4.1. The solution was heated to ∼50 ◦ C for 1h and filtered 

after it had cooled. Addition of 0.5 mL of 1.0 M KCl solution to the colorless filtrate and 

slow evaporation at room temperature led to a white, crystalline product after about two 

weeks (yield 0.39 g, 54 %). Anal. calcd. (found) for 1a: K 4.7 (4.8), Li 0.5 (0.8), W 61.8 

(61.1), P 1.7 (1.5), Sn 3.3 (3.5), C 0.7 (0.8), H 0.9 (1.0). FTIR for compound KLi-3: 

1136, 1086, 1018, 981, 952, 928, 915, 812, 693, 573, 525, 462 cm −1 . 

Fig. 3.7: FTIR spectra of compound KLi-3(red) and K 16 Li 2 [H 6 P 4 W 24 O 94 ] (blue) 

Elemental analysis was performed by Kanti Labs Ltd. in Mississauga, Canada. The 

FTIR spectrum was recorded on a Nicolet Avatar FTIR spectrophotometer in a KBr 

pellet. All NMR spectra were recorded on a JEOL Eclipse 400 instrument at room 

temperature using D 2 O as a solvent. 

35


A crystal of compound 2a was mounted on a glass fiber for indexing and intensity data 

collection at 163 K on a Bruker D8 SMART APEX CCD single-crystal diffractometer 

using Mo K α radiation [λ = 0.71073 Å]. Direct methods were used to solve the structure 

and to locate the heavy atoms (SHELXS97). Then the remaining atoms were found from 

successive difference maps (SHELXL97). Routine Lorentz and polarization corrections 

were applied and an absorption correction was performed using the SADABS program 

[81]. Crystallographic data are summarized in Table 3.2. 

Table 3.2: Crystal Data and Structure Refinement for compound KLi-3 

Emperical formula C 8 H 130 K 17 Li 11 O 235 P 8 Sn 4 W 48 

fw 14275.8 

space group (No.) P 4 2 /nmc (14) 

a (Å) 21.5112(17) 

b (Å) 21.5112(17) 

c (Å) 27.171(3) 

vol (Å 3 ) 12573(2) 

Z 2 

temp ( ◦ C) -120 

wavelength (Å) 0.71073 

d calcd (mg m −3 ) 3.72 

abs coeff. (mm −1 ) 22.69 

R [I > 2 σ(I)] a 0.045 

R w (all data) b 0.109 


Electrochemistry : General Methods and Materials 

Pure water was used throughout. It was obtained by passing through a RiOs 8 unit 

followed by a Millipore-Q Academic purification set. All reagents were of high-purity grade 

and were used as purchased without further purification. The pH = 4 medium was made 

of 1 M CH 3 COOLi + CH 3 COOH. Electrochemical Experiments. The concentration of 

polyanion 3 was 2 × 10 −4 M. The solutions were deaerated thoroughly for at least 30 min. 

with pure argon and kept under a positive pressure of this gas during the experiments. 

The source, mounting and polishing of the glassy carbon (GC, Tokai, Japan) electrodes 

36

has been described [84]. The glassy carbon samples had a diameter of 3 mm. The 

electrochemical set-up was an EG & G 273 A driven by a PC with the M270 software. 

Potentials are quoted against a saturated calomel electrode (SCE). The counter electrode 

was a platinum gauze of large surface area. All experiments were performed at room 

temperature. 


Synthesis and Structure 

Reaction of (CH 3 ) 2 SnCl 2 with K 16 Li 2 [H 6 P 4 W 24 O 94 ] in aqueous, acidic(pH 4.1) medium 

at ∼50 ◦ C resulted in[{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ] 28− 3. Single crystal X-ray analysis on 

K 17 Li 11 [{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ]·51H 2 O KLi-3 revealed that the novel polyanion 3 

is composed of two (P 4 W 24 O 92 ) fragments that are linked by four equivalent diorganotin 

groups. The unprecedented assembly 3 has D 2d symmetry and contains an empty, hydrophobic 

pocket (diameter around 2 Å) in the center of the molecule (see Figure 3.8). 

The two (P 4 W 24 O 92 ) fragments of 3 are orthogonal to each other and are held together 

by four structurally equivalent dimethyltin groups. Interestingly, the two (P 2 W 12 O 48 ) 

Fig. 3.8: Ball and stick (left), Polyhedron (right) representation of polyanion 3 

subunits of each (P 4 W 24 O 92 ) fragment are fused via four W-O-W’ bridges involving cap 

and belt tungsten centers. It remains to be seen if the ‘free’ [H 6 P 4 W 24 O 94 ] 18− precursor 

has the same connectivity, or only two W-O-W’ bridges involving the caps as originally 

suggested by Contant and Tézé [76]. We are currently trying to obtain single crystals 

of K 16 Li 2 [H 6 P 4 W 24 O 94 ] in order to resolve this open question. It is highly likely that 

37

the presence of the four (CH 3 ) 2 Sn 2+ groups causes the small angle ∼45 ◦ of the fused 

(P 2 W 12 O 48 ) groups. In agreement with our previously reported diorganotin-containing 

polyoxotungstates, the two methyl groups of each tin atom in 2 are in relative trans 

positions (C1-Sn-C2 =∼169.6(11) ◦ , see Figure 3.9. The Sn-C bond lengths in 2 are 

Fig. 3.9: Ball and stick representation of the asymmetric unit of polyanion 3 

2.12(3) and 2.19(3) Å, respectively, and the equatorial Sn-O bond lengths are 2.230(13) 

and 2.254(12) Å, respectively. The bond lengths of the tungstophosphate framework are 

not unusual. Bond valence sum calculations indicate that polyanion 3 contains only one 

type of protonated oxygen (O1A, s = 1.44) [85]. There is a total of eight O1A atoms in 

3 and they are all 2-oxo bridges (W1-O1A-Sn1) linking the four cap-tungstens of each 

(P 2 W 12 O 48 ) fragment with tin centers. The intermediate bond valence sum for O1A indicates 

that only 50% of all eight atoms are actually protonated. This probably means 

that at each cap of the two (P 2 W 12 O 48 ) units in 3 only one of the two W-O-Sn bridges 

is actually protonated. Interestingly, this is in complete agreement with the conclusions 

of Contant and Tézé in their studies of the [H 2 P 2 W 12 O 48 ] 12− and [H 2 P 4 W 24 O 94 ] 22− 

precursors.[76] All potassium ions could be identified crystallographically (K4 with half 

occupancy), but none of the lithium ions. Nevertheless, their presence and therefore the 

complete molecular formula of KLi-3 was determined by elemental analysis. 

38

Solution NMR 

Polyanion 3 is diamagnetic and contains four spin 1 nuclei 2 

(183 W, 119 Sn, 13 C, 1 H) and 

therefore represents a good candidate for solution NMR studies at room temperature. 

We also examined the solution properties of 3 by multinuclear NMR (D 2 O, ∼20 ◦ ). Our 

31 P NMR measurements resulted in two singlets (-7.1, -8.7 ppm) of equal intensity and 

1 H NMR showed a singlet at 0.7 ppm. For 119 Sn and 13 C NMR (both 1 H decoupled) 

we observed singlets at -243.2 ppm and 8.6 ppm, respectively. Although we used the 

lithium salt of 3 we were unable to observe any signals in 183 W NMR, which indicates 

that the concentration of the polyanion was too small due to very poor solubility. Close 

inspection of the structure of each (P 4 W 24 O 92 ) fragment in 3 indicates that it may be 

considered as a lacunary derivative of the well-known Preyssler ion [NaP 5 W 30 O 110 ] 14− 

[86]. This plenary polyanion has approximate D 5h symmetry and consists of a cyclic 

assembly of five (PW 6 O 22 ) units. The (P 4 W 24 O 92 ) fragments in 3 may be considered as 

being composed of a cyclic assembly of four (PW 6 O 22 ) units with a linkage pattern of the 

individual units identical to the Preyssler ion. However, due to one missing (PW 6 O 22 ) 

unit in each (P 4 W 24 O 92 ) fragment the latter is best described as a lacunary Preyssler ion. 

Electrochemistry 

The polyanion 3 was also studied by cyclic voltammetry in 1 M (CH 3 COOLi + CH 3 COOH) 

pH 4 buffer corresponding essentially to its synthesis medium. Figure 3.10A shows the 

features of interest in the overall CV of 3 in the above pH 4 medium. This CV is constituted 

by a broad first wave, followed by a large current intensity second wave which 

peaks close to the electrolyte discharge. Actually, the second multi-electron reduction 

process is a combination of two very closely-spaced waves. The decomposition products 

generated at this combined wave deposit on the electrode surface upon continuous cycling 

of the potential up to the cathodic limit shown in Figure 3.10A. The efficiency of the 

deposition process increases when the potential scan rate decreases. Specifically, a very 

faint reversibility can be detected for this combined second wave at a scan rate of 200 mV 

s −1 . Such reductive deposition phenomena at fairly negative potentials are known and 

have been described for a large variety of heteropolyanions [87]. The complex phenom- 

39

Fig. 3.10: Cyclic voltammogram of 2 × 10 −4 M solution of 3 in a pH 4 medium (1 M CH 3 COOLi + 

CH 3 COOH). The scan rate was 10 mV.s −1 , the working electrode was glassy carbon and the reference 

electrode was SCE. (A) The whole voltammetric pattern(left), (B) The voltammetric pattern restricted 

to the first redox processes (right) 

ena associated with the second combined wave will not be considered further here. The 

behavior of the first wave is more characteristic of 3 and is shown in Figure 3.10B. In the 

following, the CV pattern is restricted to this process. The cathodic part features a broad 

electrochemical wave which remains composite if the potential scan rate is lower than 

the 200 mV s −1 explored here. In contrast, two well-separated oxidation processes are 

observed on potential reversal, at - 0.612 V and - 0.356 V vs SCE, respectively, thus confirming 

the composite nature of the cathodic scan. The detailed molecular structure of the 

polyanion precursor [H 2 P 4 W 24 O 94 ] 22− before its engagement in the self-assembly process 

resulting in formation of 3 remains unknown. Nevertheless, comparison of the first wave 

system of 3 with the cyclic voltammograms of [H 2 P 4 W 24 O 94 ] 22− and the wheel-shaped 

[H 7 P 8 W 48 O 184 ] 33− in the same medium is expected to be useful. This study might allow 

us to extract some distinct features of 3 which are due to the incorporated dimethyltin 

units. All three polyanions can be considered as lacunary species and thus, their electrochemistry 

should be carried out in a well-buffered electrolyte [88]. The comparisons 

between 3 and [H 2 P 4 W 24 O 94 ] 22− on the one hand and between 3 and [H 7 P 8 W 48 O 184 ] 33− 

on the other hand, are shown in Figures 3.11, respectively. The potential locations of 

the reduction peaks and the number of electrons consumed by each wave are gathered in 

Table 3.3. 

The number of electrons for the waves of [H 7 P 8 W 48 O 184 ] 33− (three equal 8-electron 

40

Fig. 3.11: Comparison of the cyclic voltammograms of 2 × 10 −4 M solution of 3 in a pH 4 medium (1 M 

CH 3 COOLi + CH 3 COOH). The scan rate was 10 mV.s −1 , the working electrode was glassy carbon and 

the reference electrode was SCE. (A) Comparison of the voltammetric patterns of 3 and [H 2 P 4 W 24 O 94 ] 22− 

(left)(B) Comparison of the voltammetric patterns of 3 and [H 7 P 8 W 48 O 184 ] 33 (right) 

Table 3.3: Reduction peak potentials measured from CVs and number (n 1 or n 2 ) of electrons corresponding 

to each wave of 3, [H 2 P 4 W 24 O 94 ] 22− and [H 7 P 8 W 48 O 184 ] 33− The scan rate was 10 mV s −1 , the 

working electrode was glassy carbon and the reference electrode was SCE 

Polyoxometalate n 1 - E pc1 / V vs SCE n 2 - E pc2 / V vs SCE 

3 16 0.755 - - 

[H 2 P 4 W 24 O 94 ] 22− 4 0.802 4 ∼1.110 

[H 7 P 8 W 48 O 184 ] 33− 8 0.610 8 0.728 

waves)[76, 89] and [H 2 P 4 W 24 O 94 ] 22− (three equal 4-electron waves)[76] were known from 

previous works. For the first wave of 3 the corresponding number of electrons was evaluated 

in two different ways. A first rough estimate was performed by determining the 

area delimited by the relevant voltammograms and comparing the charges corresponding 

to each wave. This method was used to compare 3 and [H 2 P 4 W 24 O 94 ] 22− , which shows 

suitable, well-separated waves. The charge ratio was 4.07 in favor of 3, thus indicating 

roughly 16-electrons per molecule for the first wave of this complex. As a second method, 

controlled potential coulometry was carried out at - 0.780 V vs SCE, but the number 

of electrons consumed per molecule exceeds 16, due to a non-identified catalytic and/or 

decomposition process. Such behavior was also observed previously during coulometric 

studies on [H 7 P 8 W 48 O 184 ] 33− , albeit to a smaller extent [89]. Finally, it can be concluded 

that the result of the second method supports the value of roughly 16-electrons per molecule 

of 3 obtained by the first method. Further coulometric study of the catalytic process 

41

as a function of electrolyte composition might help to accurately determine electron numbers, 

but is beyond the scope of the present work. 

Figures 3.11 and Table 3.3 indicate unambiguously that the three polyanion species 3, 

[H 2 P 4 W 24 O 94 ] 22− and [H 7 P 8 W 48 O 184 ] 33− have distinct electrochemical properties. During 

these studies, we also observed that the stability of [H 2 P 4 W 24 O 94 ] 22− in solution is 

enhanced by formation of 2. In fact, the combined results from present and previous 

[76, 89] work allow to establish the following order of stability: [H 7 P 8 W 48 O 184 ] 33− >3 > 

[H 2 P 4 W 24 O 94 ] 22− . In agreement with literature, the CV pattern of [H 2 P 4 W 24 O 94 ] 22− is 

constituted by three separated 4-electron waves, two of which are shown in Figure 3.11A 

[76]. In Figure 3.11A and Table 3.3, these waves are located at more negative potentials 

than the sole wave considered for 3. In contrast, Figure 3.11B and Table 3.3 show 

the first two 8-electron waves of [H 7 P 8 W 48 O 184 ] 33− (already described previously)[76, 89] 

to be located at more positive potentials than that of 3. In the present case, these results 

might be interpreted based on the assumption that 3 is composed of two identical, 

mostly non-interacting moieties, a feature that would support the existence of a composite 

reduction wave. Then, the following reduction trends should be expected for the tungstenoxo-frameworks 

of the three polyoxometalates discussed here: comparing a substituted 

polyoxometalate and its lacunary precursor, binding of one or more cationic moieties to 

the latter will diminish the overall negative charge of the product polyanion. As a consequence, 

the reduction potential of the tungsten-oxo-framework will be driven in the 

positive direction compared to that of the precursor lacunary complex. One assumption 

behind this conclusion is that no specific complicating influences appear in the overall 

reduction schemes of the two polyanions. In short, the cation-substituted polyanion will 

behave much like a “saturated” complex, with a reduction potential intermediate between 

those of the plenary and lacunary parents, 3 a feature well illustrated by the reduction 

patterns of Keggin and Dawson-type tungstostannates [90]. However, this conclusion must 

be applied with caution in the general case because such a reasoning would not take into 

account any specific modification, e.g. a change in acid-base properties of the polyanion 

as a result of cation incorporation. Detailed parameters of the cation like size, electronic 

configuration and coordination geometry including possible distortions (e.g. Jahn-Teller) 

42

may also contribute to the specificity [91]. Interestingly, [H 7 P 8 W 48 O 184 ] 33− appears to 

behave as if it were more saturated than 3. However, the comparison is not straightforward 

as the linkage pattern of the (P 2 W 12 O 48 ) subunits is different in [H 7 P 8 W 48 O 184 ] 33− 

and 3 and for free [H 2 P 4 W 24 O 94 ] 22− it is not yet known. As a consequence, the acidities 

of [H 7 P 8 W 48 O 184 ] 33− ,[76] [H 2 P 4 W 24 O 94 ] 22− and 3 might also be different from each other. 

Such an assumption is supported by the splitting of the CV pattern of [H 7 P 8 W 48 O 184 ] 33− 

in two 8-electron waves at pH 4, without any possibility to make them merge until pH = 

7.3. Even then the merging is incomplete, as a slight decrease of the potential scan rate 

favors splitting of the waves. Finally, it is worth noting that for 3 no wave was observed 

which could be associated with reduction of the Sn-centers. This result is reminiscent 

of that obtained by Chorghade and Pope for Keggin and Dawson-type tungstostannates 

[90]. 

Electrochemistry studies was done by our collaborators Dr. B. Keita, and Prof. L. Nadjo, 

Université Paris-Sud, Orsay Cedex, France. 


The title polyanion 3 is of interest for several reasons, (i) it represents the first example 

of a polyanion synthesized from the [H 6 P 4 W 24 O 94 ] 18− precursor, (ii) it represents the first 

example of a polyoxoanion containing the (P 4 W 24 O 92 ) fragment, (iii) it reveals that the 

(P 4 W 24 O 92 ) fragment is a lacunary derivative of the Preyssler ion [NaP 5 W 30 O 110 ] 14− , (iv) 

it represents a novel polyanion architecture, (v) it has a central, hydrophobic pocket, 

and (vi) it adds a new member to our series of monomeric, trimeric and dodecameric 

dimethyl-tin containing polyoxotungstates. The structure of 3 allows for a multitude 

of studies including host/guest chemistry, catalysis and medicine. Some of this work is 

currently in progress and the results will be reported in due time. The first reduction wave 

in the CV pattern of 3 was studied in detail because it contains the main features useful for 

a characterization of this complex. This 16-electron, broad reduction wave is associated 

on potential reversal with two well-separated oxidation processes. As judged from the 

potential locations and current intensities, the voltammetric pattern is unambiguously 

different from those of [H 7 P 8 W 48 O 184 ] 33− and [H 2 P 4 W 24 O 94 ] 22− , even though no feature 

43

was observed that could be traced to the reduction of Sn-centers. 

3.3 The trimeric-dimethyltin containing bowl shaped 

tungstophosphate(V): Cs 12 Na 6 {Sn(CH 3 ) 2 (OH)} 3 

(Sn(CH 3 ) 2 ) 3 {A-PW 9 O 34 } 3·14H 2 O 


The title compound (CsNa-4) was synthesized by dissolving a 1.46 g (0.600 mmol) of 

Na 9 [A-PW 9 O 34 ] in 20 mL sodium acetate buffer followed by addition of 0.435 g (1.98 

mmol) of (CH 3 ) 2 SnCl 2 . This solution (pH 4.8) was heated to ∼80 ◦ C for 1 h and then 

cooled to room temperature. After filtration, 0.5 mL of 0.1 M CsCl solution was added 

and then the solution was allowed to evaporate in an open vial at room temperature. 

A white crystalline product started to appear after a week or two. Evaporation was 

continued until the solvent approached the solid product which was suitable for single 

crystal XRD, FTIR spectroscopy (see Figure 3.12) and elemental analysis. 

Fig. 3.12: FTIR spectra of compound CsNa-4(red) and Na 9 [(A-α-PW 9 O 34 )](blue,) 

44


Single crystal of CsNa-4 was mounted on a glass fiber for indexing and intensity data 


using Mo K α radiation [λ = 0.71073 Å]. Direct methods were used to solve the structure 




[81]. Crystallographic data are summarized in Table 3.4 

Table 3.4: Crystal Data and Structure Refinement for compound CsNa-4 

Empirical formula Cs 36 C 36 O 357 P 9 Sn 18 W 81 

fw 28236.2 

space group R 3m (160) 

a (Å) 29.7445(7) 

c (Å) 15.5915(7) 

vol (Å 3 ) 11946.26(67) 

Z 3 

temp. ( ◦ C) -100 


dcalc (Mg m −3 ) 3.912 

abs. coeff. (mm −1 ) 23.148 

R [I > 2 σ(I)] a 0.053 



Electrochemistry : General Methods and Materials 

Pure water was used throughout. It was obtained by passing through a RiOs 8 unit 

followed by a Millipore-Q Academic purification set. All reagents were of high-purity grade 

and were used as purchased without further purification. The pH = 4 medium was made 

of 1 M CH 3 COOLi + CH 3 COOH. Electrochemical Experiments. The concentration of 

polyanion 3 was 2 × 10 −4 M. The solutions were deaerated thoroughly for at least 30 min. 

with pure argon and kept under a positive pressure of this gas during the experiments. 

The source, mounting and polishing of the glassy carbon (GC, Tokai, Japan) electrodes 

has been described [84]. The glassy carbon samples had a diameter of 3 mm. The 

45

electrochemical set-up was an EG & G 273 A driven by a PC with the M270 software. 

Potentials are quoted against a saturated calomel electrode (SCE). The counter electrode 

was a platinum gauze of large surface area. All experiments were performed at room 

temperature. 

Electrochemistry studies was done by our collaborators Dr. B. Keita, and Prof. L. Nadjo, 

(Université Paris-Sud, Orsay Cedex, France. 



The discrete cyclic trimeric title polyanion [{Sn(CH 3 ) 2 (OH)} 3 (Sn(CH 3 ) 2 ) 3 {A-PW 9 O 34 } 3 ] 18− 

4 consists of three trilacunary A-α-[PW 9 O 34 ] 9− Keggin fragments linked to each other by 

three {Sn(CH 3 ) 2 } 2+ bridging groups and three {Sn(CH 3 ) 2 } 2+ are linked to each other 

forming a trimeric core resulting to a cyclic trimeric bowl type unprecedented structure 

with nominal C 3v symmetry. The novel dimethyl tin substituted, trimeric tungsto 

Fig. 3.13: Ball/stick (left) and Polyhedron (right) representation of polyanion 4 

phosphate(V) [{Sn(CH 3 ) 2 (OH)} 3 (Sn(CH 3 ) 2 ) 3 {A-PW 9 O 34 } 3 ] 18− 4 consists of three lacunary 

A-α-[PW 9 O 34 ] 9− Keggin fragments linked via three Sn(CH 3 ) 2+ 2 groups and three 

Sn(CH 3 ) 2+ 2 connected to each other by three (µ 2 -OH) bridges to form a cyclic core, lead- 

46

ing to a structure with nominal C 3v symmetry (see Figure 3.13). Alternatively 4 can 

be described as a trilacunary A-α-[PW 9 O 34 ] 9− fragment which has taken up three organotin 

units.The discrete cyclic trimeric title polyanion [{Sn(CH 3 ) 2 (OH)} 3 (Sn(CH 3 ) 2 ) 3 {A- 

PW 9 O 34 } 3 ] 18− 4 consist of three A-α-[PW 9 O 34 ] 9− linked to each other other by three outer 

Sn(CH 3 ) 2+ 2 bridging groups and three central Sn(CH 3 ) 2+ 2 connected by (µ 2 -OH) bridges 

forming a cyclic core which act as a cap to the polyanion resulting in a cyclic trimeric 

bowl unprecedented structure with nominal C 3v symmetry. 

The two terminal oxygen atoms from adjacent corner-shared WO 6 octahedra of each PW 9 

Keggin-type unit occupy equatorial positions of the tin coordination spheres. The “top” 

of the structure is capped by three Sn(CH 3 ) 2+ 2 connected to each other by three (µ 2 - 

OH) bridges which forms the cyclic fragment. This somewhat resembles to the structure 

[(UO 2 ) 3 (H 2 O) 5 As 3 W 29 O 124 ] 19− reported by Pope et al. [92]. However, this capping unit 

is analogous to W 3 O 13 reported by Pope et al. we have also observed the capping neutral 

fragment {As-AsW 9 } 3 in one of our dimethyltin substituted tetrameric species. The 

capping by the cyclic fragment of the plenary stucture (see Figure 3.13) forms a bowl 

shaped assembly. The trans consequence of the methyl groups makes the cavity of the 

bowl hydrophobic. 

Each outer dimethyltin group is coordinated through equatorial positions to two terminal 

oxygen atom of edge-shared WO 6 octahedra belonging to two adjacent Keggin units. The 

two methyl groups are trans to each other, which had been reported previously by Kortz 

et al. The three dimethyltin groups in the core are coordinated to each other as well as 

to two terminal oxygens of corner-shared WO 6 octahedra belonging to different (W 3 O 13 ) 

triad. However, the coordination numbers (6) of all the tin centers in 4 are equivalent. 

The structural indifference between the outer and the core tin atoms is more pronounced 

due to significant difference in the C-Sn-C bond angle. Specifically, C-Sn1-C (175.530(2) ◦ ) 

is significantly higher than the C-Sn2-C (153.670(1) ◦ ), most probably due to the oxygen 

bridging the inner dimetyltin core. (See Figure 3.14) 

Bond-valence-sum (BVS) calculations for 4 indicated that no oxygen of the three 

(A-α−PW 9 O 34 ) caps is protonated [85]. However, oxygen of the three (µ 2 -OH) bridges, 

which forms a cyclic core is protonated. 

47

Fig. 3.14: The central core of Sn(CH 3 ) 2 2+ connected to each other by three (µ 2 -OH) bridges 

Electrochemistry 

The polyanion 4 was also studied by cyclic voltammetry in 1 M (CH 3 COOLi + CH 3 COOH) 

pH 4 buffer corresponding essentially to its synthesis medium. Among the isomers of PW 9 , 

A-α-PW 9 O 34 was used as the lacunary precursor for the synthesis of the trimer. X-ray 

crystallography indicates that the three such ligands present in this trimer keep their 

original structure in the final complex. However, the problem of the behaviours of the 

trimer in solution must be considered. As a matter of fact, following the conclusions of 

detailed studies published by Contant and Hervé [93], A-α-PW 9 O 34 alone is known to 

undergo, in solution, a series of transformations that generate α-PW11. Therefore, it was 

necessary to check whether the solid state structure of the trimer with three A-α-PW 9 O 34 

moieties was likely to be retained or not in solution. A pH = 4 medium was selected 

for this work. This study was facilitated by the following remark: among the isomers of 

PW 9 fairly stable in solution, A-α-PW 9 O 34 turned out to show a voltammetric pattern 

different from those of the others and which can be considered as its fingerprint. 

Such a voltammogram is represented in Figure 3.15A and is characterized by a welldefined 

four-electron reduction wave, associated, on potential reversal, with a broad oxidation 

wave. The CV run for the trimer, in the same potential domain, shows the same 

shape as that of A-α-PW 9 O 34 . These CVs are clearly distinct from that featuring the 

redox behaviours of PW 11 which is comprised of two two-electron reversible waves [79, 94]. 

48

Fig. 3.15: Cyclic voltammogram of 2 × 10 −4 M solution of 4 in a pH 4 medium (1 M CH 3 COOLi + 

CH 3 COOH). The scan rate was 10 mV.s −1 , the working electrode was glassy carbon and the reference 

electrode was SCE. (A) Superposition of the CVs restricted to the first redox pattern for trimer and A-α- 

PW 9 O 34 respectively.(left), (B) Complete CV for the trimer showing the presence of a second irreversible 

wave close to the electrolyte discharge. (right) 

The presence of a tiny reversible wave negative of the main reduction peak must be remarked, 

both in the CV of the trimer and that of A-α-PW 9 O 34 . The potential location of 

this wave suggests the existence of trace amounts of PW 11 [94]. Furthermore, the current 

intensity of this new wave depends on the delay between the preparation of the solution 

of trimer or A-α-PW 9 O 34 and the recording of the CV. However, as an example, it must 

be noted that several hours are necessary before significant amounts of PW 11 could be 

observed in media of pH 4 to 5. The current intensity for the trimer solution is larger 

than that of A-α-PW 9 O 34 for identical concentrations of the complexes in solution. Even 

so, it reaches only 58.7% of the expected intensity if a complete decomposition of the 

trimer giving the A-α-PW 9 O 34 fragments free in solution were assumed. This difference 

in current intensities might be attributed to the difference in diffusion coefficients, that 

for the trimer being smaller than that for A-α-PW 9 O 34 . Comparison of other characteristics 

of the CVs of the trimer and of A-α-PW 9 O 34 support this hypothesis: the trimer 

is reduced at a more positive potential than A-α-PW 9 O 34 (the reduction peak potentials 

Ep are - 0.732 V and - 0.753 V respectively); and particularly, the overall electron transfer 

process associated with the redox couples, as evaluated from the anodic-to-cathodic 

peak potentials difference, are faster in the case of the trimer (△ Ep = 0.105 V) than for 

A-α-PW 9 O 34 (△ Ep = 0.160 V). This observation might be attributed to the presence 

of Sn-moieties attached to A-α-PW 9 O 34 fragments that modify the lacunary character 

49

of these fragments [88, 90]. For completeness, Figure 3.15B shows that, upon extending 

the potential domain in the negative direction, the CV of the trimer has a second wave 

peaking at - 0.840 V and which is irreversible. The corresponding wave for A-α-PW 9 O 34 

(not shown) appears at still more negative potential and is very close to the electrolyte 

limit. The reduction product(s) generated in the potential domain of this plurielectronic 

wave do not modify the electrode surface: as a matter of fact, it is observed that the 

characteristics of the first redox couple are maintained when a new voltammogram is 

run with this electrode. This behaviour is different from that observed with numerous 

plenary polyoxometalates of the Keggin and Dawson series: the reduction products generated 

on their last several-electron waves, modify irreversibly and persistently electrode 

surfaces [87, 95]. Finally, it must be pointed out that no reduction process is observed 

for the Sn-centers, a feature in agreement with Pope’s studies on Sn-substituted polyoxometalates 

[90] and our own recent work on the dimeric, tetrakis-dimethyltin assembly 

[{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ] 28− . 


Furthermore, 4 represents the member of a novel family of diorganotin-polyanion based 

cage complexes. The structure of 4 reveals that (a) the dimethyltin unit acts as a linker of 

three (A-α-PW9O34) Keggin-type fragments, (b) the linkage is achieved via two, coplanar 

Sn-O(W) bonds with each of the Keggin fragments, (c) the methyl groups of the incorporated 

dimethyltin units are oriented trans to each other, (d) the incorporated dimethyltin 

units are oriented such that one of the two methyl group points inside the central polyanion 

cavity forming a bowl type assembly, (e) the tin atoms of the incorporated dimethyltin 

units have octahedral coordination geometries, (f) dimethyltin substituted polyanions 

tend to form cage-like structures, (g) the dimethyltin unit is an ideal, hydrolytically stable, 

sterically not too demanding building block/linker for the design of nanomolecular 

bowl type assembly, (h) the CV of the trimer has the same shape as that of its precursor 

lacunary species, A-A-α-PW 9 O 34 , thus indicating the presence of the latter without isomerization 

in the complex or free in solution. 

(Manuscript in preparation) 

50

3.4 The tetrameric, chiral tungstoarsenate(III), 

({Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }As 3 {α-AsW 9 O 33 } 4 ) 21− 


The tetrameric polyanion (KNH4-5) was synthesized by interaction of 0.15 g (0.66 mmol) 

(CH 3 ) 2 SnCl 2 with 1.58 g (0.30 mmol) K 14 [As 2 W 19 O 67 H 2 O] in 20 mL H 2 O at pH 4.1. The 

solution was heated to ∼80 ◦ C for 1 h and filtered after it had cooled. Addition of 0.5 mL 

of 1.0 M NH 4 Cl solution to the colorless filtrate and slow evaporation at room temperature 

led to 0.72 g (yield 67 %, based on As) of a white crystalline product after about one 

week.Anal. calcd. (found) for KNH4-5: K 2.6 (2.4), N 1.8 (1.9),W 61.7 (61.1), As 4.9 

(4.9), Sn 3.3 (3.1), C 0.7 (0.8), H 1.2 (1.0). 

Fig. 3.16: FTIR spectra of compound KNH4-5(red) and Na 9 [α-AsW 9 O 33 ](blue) 


Single crystal X-ray analysis on K 7 (NH 4 ) 14 [(Sn(CH 3 ) 2 ) 3 (H 2 O) 2 As 3 (α-AsW 9 O 33 ) 4 ]·26H 2 O 

KNH4-5. A crystal of compound KNH4-5 was mounted on a glass fiber for indexing 

and intensity data collection at 163 K on a Bruker D8 SMART APEX CCD single-crystal 

51

diffractometer using Mo K α radiation [λ = 0.71073 Å]. Direct methods were used to 

solve the structure and to locate the heavy atoms (SHELXS97). Then the remaining 

atoms were found from successive difference maps (SHELXL97). Routine Lorentz and 

polarization corrections were applied and an absorption correction was performed using 

the SADABS program [81]. Crystallographic data are summarized in Table 3.5 

Table 3.5: Crystal Data and Structure Refinement for compound KNH4-5 

Emperical formula As 7 C 6 H 130 K 7 N 14 O 160 Sn 3 W 36 

fw 10732.3 

space group (No.) P 2 1 /c (14) 

a (Å) 22.612(2) 

b (Å) 19.954(2) 

c (Å) 41.099(4) 

vol (Å 3 ) 18237(3) 

Z 4 

temp ( ◦ C) 27 


d calcd (mg m −3 ) 3.72 

abs coeff. (mm −1 ) 24.53 

R [I > 2 σ(I)] a 0.170 




The title polyanion 5 is composed of four (B-α -AsW 9 O 33 ) fragments that are linked by 

three dimethyltin groups and three As(III) atoms resulting in an unprecedented, chiral 

cage-like assembly with C 1 symmetry (Figure 3.17, left).Polyanion 5 can also be described 

as a trimeric assembly [{Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }(α-AsW 9 O 33 ) 3 ] 21− (Figure 

3.17, right) which is capped by a fourth (α-AsW 9 O 33 ) Keggin fragment via three trigonal 

pyramidal As(III) linkers (Fig.3.18). Interestingly, the [As 3 (α-AsW 9 O 33 )] capping unit is 

formally neutral. The three As(III) linkers are coordinated by two oxygens of a Keggin 

unit from the triangular assembly and by one oxygen of the unique Keggin unit. As a result, 

only three of the six belt tungsten atoms of the unique (AsW 9 O 33 ) unit are involved 

in the bonding to adjacent Keggin building blocks in an alternating fashion. 

52

Fig. 3.17: Top view of [{Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }As 3 (α -AsW 9 O 33 ) 4 ] 21− (5).(left),the unique AsW 9 

fragment and its three associated As linkers are not shown for clarity.The octahedra represent WO 6 and 

the balls are tin (green), arsenic (yellow), carbon (blue) and oxygen (red). Hydrogen atoms are omitted 

for clarity.(right) 

The orientation of this unique Keggin unit with respect to the triangular tri-Keggin 

fragment is the reason why 5 is chiral (Figure 3.17). The dimethyltin groups are coordinated 

to two oxygens of each of the adjacent Keggin units and two methyl groups 

which are in trans-positions, as had been observed previously for [{Sn(CH 3 ) 2 } 3 (H 2 O) 4 (β- 

XW 9 O 33 )] 3− (X = As III , Sb III ). However, the coordination number and geometry of the 

three tin centers in 5 is not equivalent. One of the tin atoms (Sn1) is six-coordinated (octahedral) 

whereas the other two tin atoms (Sn2, Sn3) are seven−coordinated (pentagonal 

bipyramidal) due to an additional terminal water ligand in the equatorial plane(Sn2−OH2 

2.285(19), Sn3−OH2, 2.49(4) Å). The Sn1−O(W) bonding can be described as two short 

bonds (2.091, 2.095(17) Å) and two very long bonds (2.400, 2.457(17) Å). On the other 

hand, the Sn2−O(W) bond lengths (2.300, 2.354, 2.372, 2.478(17) Å) and the Sn3−O(W) 

bond lengths (2.220, 2.282, 2.308, 2.462(17) Å) indicate three long bonds and one very 

long bond around the tin centers. The structural inequivalence between Sn1 on one side 

and Sn2 and Sn3 on the other side is further reflected by the C−Sn−C angles. Specifically, 

the C−Sn1−C angle (159.7(10) ◦ C) is significantly smaller than the C−Sn2−C (169.0(9) 

◦ C) and C−Sn3−C (172.4(11) ◦ C) angles, respectively. Polyanion 5 was synthesized in 

a simple one-pot procedure in aqueous, acidic medium by reaction of (CH 3 ) 2 SnCl 2 with 

K 14 [As 2 W 19 O 67 H 2 O]. We have also tried to prepare 5 by a more rational procedure (e.g. 

53

Fig. 3.18: Side view of [{Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }As 3 (α-AsW 9 O 33 ) 4 ] 21− The color code is the same 

as in above. 

3 (CH 3 ) 2 SnCl 2 + 4 Na 9 [AsW 9 O 33 ] + 1.5 As 2 O 3 ), but without success. Bond valence 

sum calculations indicate that the water molecules attached to Sn2 and Sn3 represent 

the only protonation sites in 5 [85]. All potassium ions in KNH 4 -5 could be identified 

crystallographically, but some of them are disordered resulting in partial (0.5) occupancy. 

They are located all around 5 and are coordinated to bridging and terminal oxygens of 

the polyanion. We could not identify water molecules or cations in the central cavity 

of the cage-like structure. It appears that the hydrophobic nature of the pocket and its 

small size do not allow for inclusion of the available guests. It is difficult to determine 

the exact dimensions of the cavity due to the three bridging As centers and their lone 

pairs of electrons pointing inside the pocket. Nevertheless, we estimate the diameter of 

the idealized spherical cavity to be around 3.5 Å. Interestingly, the three surface pores of 

5 involving the unique Keggin unit are larger than the central cavity (around 7 Å). 

Solution NMR 

We also examined the solution properties of 5 by multinuclear NMR (D 2 O, ∼20 ◦ C). 

Our 119 Sn NMR measurements resulted in 2 singlets (−147.8, −158.4 ppm) with intensity 

54

atios 1:2, for 13 C NMR we observed a singlet at 7.4 ppm and for 1 H NMR we obtained 

a singlet at 0.9 ppm. This is in agreement with the solid state structure of 5, which 

indicates the presence of two magnetically inequivalent tin atoms. The peak at −158.4 

ppm is assigned to the seven−coordinated Sn2 and Sn3, whereas the signal at −147.8 

is due to the six−coordinated Sn1. It can be noticed that the magnetically inequivalent 

Sn2 and Sn3 cannot be distinguished by 119 Sn NMR spectroscopy. Apparently the chiral 

nature of 5, which is induced by a rotated binding mode of the unique (AsW 9 O 33 ) Keggin 

fragment, does not protrude all the way to the other end of the molecule. Therefore, 119 Sn 

NMR spectroscopy provides only information about the local coordination environment of 

Sn2 and Sn3. The same conclusions can be drawn based on the 1 H and 13 C NMR results 

for 5, as all six methyl groups appear as magnetically equivalent. The actual symmetry 

of 5 in solution could be shown best by 183 W NMR, but unfortunately we were not able 

to obtain high quality spectra to date. This may be due to the very large number of 

expected peaks (up to 36). 


The title compound 5 represents the first polyanion containing dimethyltin and arsenic(III) 

linkers at the same time. Furthermore, 5 represents the first member of a novel family 

of diorganotin−polyanion based cage complexes. The structure of 5 reveals that (a) the 

dimethyltin unit acts as a linker of two (B-α-AsW 9 O 33 ) Keggin−type fragments, (b) the 

linkage is achieved via two, coplanar Sn−O(W) bonds with each of the Keggin fragments, 

(c) the methyl groups of the incorporated dimethyltin units are oriented trans 

to each other, (d) the incorporated dimethyltin units are oriented such that one of the 

two methyl group points inside the central polyanion cavity, (e) the tin atoms of the 

incorporated dimethyltin units can have octahedral as well as pentagonal−bipyramidal 

coordination geometries, (f) the diamagnetic nature of the dimethyltin unit allows for 

the use of multinuclear NMR as a structural characterization technique, (g) dimethyltin 

substituted polyanions tend to form cage-like structures, (h) the dimethyltin unit is an 

ideal, hydrolytically stable, sterically not too demanding building block/linker for the 

design of nanomolecular containers, (i) it is possible to prepare discrete, supramolecular 

55

host−guest systems with large cavities and a highly porous surface, and finally (j) we have 

discovered a novel class of polyanions which is of major interest for medicinal applications 

(e.g. antiviral) due to a unique combination of important properties (e.g. discrete, 

nanomolecular anion, stable at physiological pH, tightly bound organic moieties on surface, 

rational modification of steric and electrostatic surface properties). In summary, 

the large number of available Keggin− and Dawson−based lacunary polyanion precursors 

allows for an array of novel structural architectures to be envisioned. In addition, the 

possibilty of studying the mechanism of formation of such compounds accompanied by 

detailed investigations of applied (e.g. medicine) and academic (e.g. topology) properties 

indicate that 5, as well as the novel family of polyoxometalates it represents, will attract 

the attention of scientists from many different disciplines. 

3.5 The gigantic, ball-shaped heteropolytungstates 

({Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-XW 9 O 34 ) 12 ) 36− 

(X= P V , As V ) 


(a)Preparation of Cs 14 Na 22 [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ]·149H 2 O (Cs- 

6): A 1.46 g (0.600 mmol) sample of Na 9 [A-PW 9 O 34 ] [73] was added with stirring to 

a solution of 0.435 g (1.98 mmol) (CH 3 ) 2 SnCl 2 in 20 mL H 2 O. The pH was adjusted 

to 4 by addition of 4 M HCl. This solution was heated to ∼80 ◦ C for 1 hour and 

then cooled to room temperature and filtered. Addition of 0.5 mL of 1.0 M CsCl 

solution to the colorless filtrate and slow evaporation at room temperature led to a 

white crystalline product after about one week. Yield: 1.3 g (69 %). FTIR spectroscopy: 

1084(s), 1070(s), 1019(m), 977(sh), 961(sh), 945(s), 928(s), 882(m), 833(s), 

774(vs), 719(vs), 668(m), 640(sh), 596(w), 574(w), 520(m), 495(sh), 478(w), 465(w) 

cm −1 . Anal. Calcd for Cs-6: Cs, 5.0; Na, 1.4; W, 52.8; Sn, 11.4; P, 1.0; C, 2.3; H, 

1.5. Found: Cs, 4.6; Na, 1.2; W, 53.6; Sn, 11.9; P, 1.2; C, 2.5; H, 1.2. (b)Preparation 

of Cs 14 Na 22 [Sn(CH 3 ) 2 (H 2 O) 24 Sn(CH 3 ) 212 (A-AsW 9 O 34 ) 12 ]·149H 2 O(Cs-7): The synthesis 

56

Fig. 3.19: FTIR spectra of compound Cs-6(red) and Na 9 [A-PW 9 O 34 ](blue) 

of this compound was analogous to Cs-6, but instead of Na 9 [A-PW 9 O 34 ] we used 1.59 g 

(0.600 mmol) of Na 8 H[A-AsW 9 O 34 ] (synthesized according to Bi et al., [72]and the pH 

was adjusted to 3. Yield: 1.2 g (63 %). FTIR spectroscopy: 1015(sh), 983(sh), 951(s), 

901(sh), 863(s), 840(sh), 773(s), 715(s), 658(s), 578(sh), 520(w), 484(w), 471(w), 411(m) 

cm −1 . Anal. Calcd for Cs-7: Cs, 4.9; Na, 1.3; W, 52.1; Sn, 11.2; As, 2.4; C, 2.3; H, 1.5. 

Found: Cs, 4.5; Na, 1.2; W, 53.1; Sn, 11.6; As, 2.6; C, 2.4; H, 1.6. Elemental analyses were 

Fig. 3.20: FTIR spectra of compound Cs-7(red)and Na 8 H[A-AsW 9 O 34 ](blue) 

performed by Kanti Labs Ltd. in Mississauga, Canada. Both compounds crystallized as 

mixed cesium-sodium salts and are in fact isomorphous. Due to the high symmetry of 

the solid state arrangement (space group I m¯3). 

57


Single crystal X-ray analysis on Cs 14 Na 22 [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ] 

·149H 2 O Cs-6and Cs 14 Na 22 [Sn(CH 3 ) 2 (H 2 O) 24 {Sn(CH 3 ) 2 } 12 (A-AsW 9 O 34 ) 12 ]·149H 2 O Cs- 

7. The respective crystals were mounted on a glass fiber for indexing and intensity data 


using Mo K α radiation (λ = 0.71073 Å). Direct methods were used to solve the structure 





Table 3.6: Crystal Data and Structure Refinement for compounds Cs-6 and Cs-7 

crystal system Cubic Cubic 

Empirical formula C 72 H 562 Cs 14 Na 22 O 581 P 12 Sn 36 W 108 C 72 H 562 As 12 Cs 14 Na 22 O 581 Sn 36 W 108 

fw (g/mol) 37593.3 38120.7 

space group I m¯3 (204) I m¯3 (204) 

a Å 32.7441(4) 32.8121(4) 

volume (Å 3 ) 35107.44(74) 35326.62(75) 

Z 2 2 

temp. ( ◦ C) -100 -100 

wavelength (Å) 0.71073 0.71071 

dcalc (mg m −3 ) 3.488 3.516 

R [I > 2 σ(I)] a 0.0635 0.0564 

R w (all data) b 0.0635 0.0564 


The asymmetric unit of Cs-6 and Cs-7 is very small and includes only 5 tungsten 

and two tin atoms (see Figure 3.21 ). 

The spherical structure of Cs-6 and Cs-7 is truly spectacular in terms of geometry 

and size (diameter of 30 Å) and is completely unprecedented in polyoxotungstate 

chemistry (see Figures 3.22). This supramolecular assembly is composed of 12 trilacunary 

[A-XW 9 O 34 ] 9− (X = P v , As v ) Keggin fragments which are linked by a total of 36 

dimethyltin groups (12 inner (CH 3 ) 2 Sn 2+ and 24 outer (CH 3 ) 2 (H 2 O)Sn 2+ groups) resulting 

in a polyanion with T h symmetry. Interestingly, Cs-6 and Cs-7 have almost 1000 

atoms and a molar mass of around 33000 g/mol. In addition, 14 cesium ions are closely 

58

Fig. 3.21: Ball and stick representation of the asymmetric unit of Cs-6 and Cs-7 showing the same 

labeling scheme as both compounds are isostructural 

Fig. 3.22: Left:Ball and stick representation of Cs-6 and Cs-7 including the 14 cesium counter ions. The 

color code is as follows: tungsten (black), tin (blue), phosphorus/arsenic (yellow), oxygen (red), carbon 

(green) and cesium (purple). No hydrogens are shown for clarity, Right:Polyhedral representation of Cs-6 

and Cs-7. The WO 6 octahedra are red and the XO 4 tetrahedra (X = P, As) are yellow. Otherwise, the 

labeling scheme is the same as in Figure 3.21A. No hydrogens and cesiums shown for clarity 

associated with Cs-6 and Cs-7 in the solid state. They are located in hydrophilic surface 

pockets of the spherical clusters, thereby stabilizing the assembly further (see Figure 3.22 

Left). 

59

3.5.2 Results and discussions 

Polyanions Cs-6 and Cs-7 represent the second largest, discrete polyoxotungstates ever 

reported [96]. Furthermore, the overall shape of Cs-6 and Cs-7 resembles Müllers 

Keplerates which are highly-symmetrical polyoxomolybdates [97]. This class of compounds 

is characterized by spherical clusters with icosahedral symmetry of the type 

(pentagon) 12 (linker) 30 where the centers of the 12 pentagons span an icosahedron and 

the centers of the 30 linkers an icosidodecahedron. Close inspection of the structure of 

Cs-6 and Cs-7 indicates that it is best described as a ‘pseudo Keplerate’. Although the 

12 hetero atoms (P in Cs-6 and As in Cs-7) span an almost perfect icosahedron (see 

Figure 3.23), the 12 inner tin atoms do not (see Figure 3.24A). Interestingly, also the 24 

Fig. 3.23: Representation of the icosahedron spanned by the hetero atoms of Cs-6(P) and Cs-7(As) 

outer Sn atoms form a highly symmetrical arrangement (see Figure 3.24B) and so do the 

14 cesium ions which span a hexa-capped cube (see Figure 3.25). Therefore polyanions 

6 and 7 exhibit some analogies with a Russian doll, but are in fact more complex as the 

shells have varying size, symmetry and chemical composition. The multi-shell nature of 6 

and 7 is nicely visible in Figure 3.26 (cesium ions not included for clarity). Bond valence 

sum calculations (BVS) of 6 and 7 indicate that the terminal oxygens attached to the 24 

outer tin atoms are actually water molecules. There are no other protonation sites on 6 

60

Fig. 3.24: Left:Representation of the polyhedron spanned by the 12 inner tin atoms of 6 and 7.Right: 

Representation of the polyhedron spanned by the 24 outer tin atoms of Cs-6 and Cs-7 

Fig. 3.25: Representation of the hexa-capped cube spanned by the 14 cesium ions of Cs-6 and Cs-7 

and 7 and therefore the charge must be -36 [85]. This is fully consistent with elemental 

analysis, which indicated the presence of 14 cesium and 22 sodium ions. The former could 

be identified by X-ray diffraction, but not the latter which is probably due to disorder. 

The central cavity of the ball-shaped 6 and 7 has a diameter of around 8 Å and it does not 

contain any water molecules or other ions. It can be noticed that the pocket is actually 

hydrophobic because it is lined by a total of 12 methyl groups. This probably explains 

why polyanions 6 and 7, which were synthesized in aqueous medium, do not contain any 

guests. Nevertheless, we believe that in principle small guest molecules with appropriate 

61

Fig. 3.26: Ball and stick representation of Cs-6 and Cs-7 highlighting the different polyhedral shells 

(12 inner Sn atoms: red, 12 hetero atoms: purple, 24 outer Sn atoms: yellow)Courtesy: Dr. H. Bögge, 

University of Bielefeld, Germany. 

size and polarity can be encapsulated during formation of 6 and 7. Furthermore, we identified 

hydrophobic channels (lined by methyl groups) passing through the entire structure 

of 6 and 7, which could allow for loading and discharging of guest molecules also after 

the polyanions have been formed. In addition the surface of 6 and 7 has a total of 14 

hydrophilic pockets, which are all occupied by cesium ions (see Figure 3.22). 

Solution NMR 

We also investigated the solution properties of 6 by multinuclear solution NMR ( 183 W, 

119 Sn, 31 P, 13 C, 1 H) at room temperature in D 2 O using a 400 MHz JEOL ECX instrument. 

The 183 W NMR spectrum of 6 exhibits two singlets at -134.0 and -157.9 ppm, respectively, 

with an intensity ratio 1:2. The 31 P NMR spectrum of 6 shows a singlet at -13.1 ppm. 

The 119 Sn NMR spectrum of 6 shows a peak at -170.8 ppm. The 13 C NMR spectrum 

exhibits two peaks at 22.1 and 8.4 ppm, respectively, with an intensity ratio 1:2 and 1 H 

NMR also shows two peaks at 1.9 and 0.8 ppm, respectively, with an intensity ratio 1:2. In 

summary, for solutions of 6 we identified 2 types of W, 1 type of P, and 2 types each of C 

and H by NMR. The 183 W NMR results indicate that all 12 Keggin units are magnetically 

equivalent and the 6 belt tungsten atoms (-157.9 ppm) can be distinguished from the 3 

cap tungstens (-134.0 ppm). As expected, all 12 P atoms are fully equivalent. We do not 

62

Fig. 3.27: 31 P(Left), and 183 W NMR spectra of 

Cs 14 Na 22 {Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ]·149H 2 O 

have a good explanation why solution NMR does not allow to distinguish the two types of 

tin atoms which we identify based on the crystal structure (see Figures 3.26). The same 

is true for the number and relative intensities of the 13 C and 1 H peaks. 

3.5.3 STM studies of Cs-6 

The scanning tunneling microscope (STM) [98] has become an important tool to image 

surface with atomic resolution. There has been particular interest in recent years to obtain 

images of individual molecules adsorbed on surfaces, even if these substances are 

insulating in their bulk structure [99, 100]. Many insulating materials have been successfully 

imaged using STM by depositing these materials on conductive substrates [101]. 

Particularly polyoxometalates (POMs) which form self-assembled monolayers as well as 

individual species in a periodic arrangement on different substrates were imaged by STM 

at small bias voltages [101–106]. This is surprising, since the gap energy between highest 

occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbital (LUMO) 

of the isolated molecules is relatively large. One possible explanation of this type of 

imaging could be the decrease of the HOMO-LUMO energy gap due to molecule-molecule 

or molecule-substrate interactions [107]. Although the STM is capable of atomic resolution 

when imaging solid surfaces, mapping of large, complex molecules with submolecular 

resolution is a difficult task. An STM image contains both geometric and electronic information 

about the sample in a complicated way [108–110]. Highly resolved STM images 

63

can distinguish between different molecules with very similar geometric structures. As, 

for example, we would consider the van der Waals surface of large and complex molecules, 

we would see only a featureless “blob“ of a large cluster of atoms. However, spectroscopic 

possibilities of STM allow us to probe electronic states of the molecules as a function of 

energy [111, 112]. If there would be subunits of the molecule exhibiting a special type 

of chemical bonding, STM spectroscopy therefore allows filtering out special features of 

the species if they arise at much different energies. The objective of this present work is 

to achieve topographic as well as spatially resolved electronic structural information of 

ball-shaped heteropolytungstate complexes. Scanning tunneling microscopy (STM) and 

scanning tunneling spectroscopy (STS) were performed on single molecules adsorbed onto 

HOPG. Several groups have been reported the formation of ordered and monolayer arrays 

of POMs on surfaces and have imaged these using STM [101–106, 113, 114]. However, 

in our case we concentrate on isolated, free standing single molecules in order to find out 

specific features of the electronics properties at the single- molecule level. Recently the 

investigations of specific functionalities of molecular nanostructures at surfaces were reviewed 

[115, 116]. STS measurements are very often carried out under ultra high vacuum 

conditions with low temperatures to increase signal-to-noise ratio [117, 118]. However, 

it has been shown that under certain conditions STM experiments are also capable to 

detect local electronic properties at room temperature [119–121]. A home-made scanning 

tunneling microscope was used for measurements. The microscope was equipped 

with a commercially available low current control system (RHK Technology). Samples 

of Cs-6 on HOPG were conveniently prepared by allowing 10 −9 M aqueous solutions of 

pH 4 to 6 to evaporate under air. HOPG is one of the best studied substrate concerning 

its electronic properties both experimentally and theoretically [122]. Before adding the 

solution onto the substrate surface, we ensured that the tunneling tip had a sufficiently 

high resolution. We calibrated distances in the STM images by observing atomic spacing 

on highly oriented pyrolytic graphite (HOPG). Typically, for the STM measurements, 

tunneling currents between 5 and 200 pA were employed. The bias voltage was 50 mV 

to 500 mV. The scan frequency was varied between 2 and 5 Hz. Resolution was 256×256 

points for topography, and 128×128 in the STS measurements. STS studies have been 

64

performed in the current imaging tunneling spectroscopy mode (CITS) simultaneously 

with constant current image by the interrupted-feedback-loop technique. This was carried 

out by opening the feedback loop to fix the separation between the tip and sample, 

and ramping the bias voltage over the range of interest. The scan range of voltages was 

typically from -1 V to 0.1 V relative to the tip potential for 113 discrete voltage steps. 

Typically, tunneling resistances of the order of 5 G were set. We used mechanically cut 

Pt-Ir (90/10) tips from wires with a diameter of 0.25 mm. 

Results and discussion on STM studies of Cs-6 

The chemical structure of [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ] 36− 6 complex 

is represented in Figure 3.22. Molecular ordering on a surface is controlled by a delicate 

balance between intermolecular forces and molecule-substrate interactions. As the bonding 

of the complex supramolecules to the substrate is weak, diffusion is possible along 

the surface. The mobility is reduced at defects, e.g. monoatomic graphite steps. Thus 

an aggregation of molecules is to be expected, particularly in such places. In very dilute 

conditions, the supramolecules get trapped along the defects of HOPG surface. High resolution 

STM images with increasing magnification of Cs-6 are depicted in Figure 3.28. 

The images reveal the well-ordered distribution and adsorption geometry of Cs-6 even at 

room temperature. The molecules are attached to the graphite defects in a linear fashion. 

Individual molecules were clearly distinguished and measured. The substrate was easily 

imaged simultaneously with the molecules. Figure 3.28 shows both, the substrate and 

adsorbate, and can help to derive the exact adsorption geometry. The periodicity of the 

molecules is larger than the size of the individual molecules. This might have caused due to 

the strong repulsive forces between the large ion complexes. The apparent size of the molecules 

in the STM images is in accordance with the calculated molecular size from X-ray 

structure of 3 nm. The six-fold symmetry of the molecule is clearly discernible. In order 

to study the electronic properties of [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ] 36− 

complex we applied CITS technique. CITS is current imaging tunneling spectroscopy 

and has been developed for scanning tunneling spectroscopy (STS) of a sample surface 

[123, 124]. CITS involves the measurement of the I-V characteristics at each pixel that the 

65

Fig. 3.28: STM pictures of {Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ] 36− 

normal STM topography is taken. The tip to sample distance is defined by the topography 

parameters. One then has a normal STM image as well as current images, where the 

current images are obtained from the three-dimensional data structure of I (V, x, y). The 

current image thus represents a slice, at a given voltage, of the current as a function of the 

lateral x, y coordinates. Variations on this scheme can be performed whereby I-V characteristics 

are recorded at a subset of points in a grid or along a particular line in an image. 

The current contrast changes significantly when at certain bias voltages new molecular 

energy levels come into play thus enhancing the information obtained from topography 

alone. The use of current imaging, in particular with conductance measurements, allows 

energy-resolved spectroscopy to be performed with spatial emphasis. One can see the 

location of states as a function of energy and position [125]. CITS technique has been 

applied successfully to semiconductor materials but its application to organic molecules 

is rather difficult because of mobility or instability of the molecules, drift, etc [126]. With 

our home built low drift STM head we successfully applied this technique to the P-ball 

shaped complex, Figure 3.22 but we did not see any remarkable features in current images 

from voltages 0.1 to below -1.0 V. We assume that [A-PW 9 O 34 ] 9− fragments of the 

complex, Figure 3.28 could be far away from the Fermi level. That’s why these states do 

not play a significant role in the tunneling current up to the applied voltage [127]. 

The STM studies was done by our collaborators Prof. P. Müller and his coworkers Mr. M. 

S. Alam, V. Dremov, Physikalisches Institut III, (Universität Erlangen-Nürnberg, Germany. 

66

3.5.4 HPPS measurement 

The dynamic light scattering measurements was done on a freshly synthesized solution and 

crystal redissolved of polyanion 6 and solution of polyanion 7 in collaboration with Prof. 

M. Winterhalter and his group (IUB, Germany). The data obtained from high performance 

particle sizer(HPPS) provided by Malvern instruments, suggest that the polyanion 

6 were monodispersed. The size distribution by intensity for polyanion showed two kinds 

of particle, a size of diameter 148 nm and 1.1 nm but size distribution by number and 

suggest that the particle of size 1.1 nm is more populated. (See Figure.3.29) 

The light scattering experiment for polyanion 7 suggest that the polyanion were monodis- 

Fig. 3.29: Size distribution by intensity and number of polyanion 6 

persed in solution and have identical size distribution by intensity and number which 

indicated that only one kind of particle size (1.2 nm), were seen to be populated. (See 

Figure.3.30) Crystal of polyanion Cs-6 were redissolved in same concentration of the 

Fig. 3.30: Size distribution by intensity and number of polyanion 7 

synthesized solution. The light scattering experiment suggest that the polyanion were 

monodispersed in solution and have identical size distribution by intensity and number 

which indicated that only one kind of particle size (126 nm), were seen to be populated. 

(See Figure.3.31) A detailed study on dynamic light scattering of polyanion 6 and polyan- 

67

Fig. 3.31: Size distribution by intensity and number of polyanion Cs-6 

ion 7 are on progress to understand the dynamic behavior of the polyanion in solution 

and for the redissolved crystal. All the measurement were done in aqueous medium in a 

polystyrene cuvette. 


In summary, we have synthesized the supramolecular, spherical polyoxotungstate assemblies 

Cs-6 and Cs-7 using a simple one-pot procedure in aqueous medium. The structures 

of these compounds are completely unprecedented and allow for a multitude of studies including 

host/guest chemistry, ion exchange, gas storage, catalysis and medicine. We have 

demonstrated that the dimethlytin group is a highly reactive electrophile which allows to 

link lacunary polyanion fragments in an unprecedented fashion. The resulting compounds 

are diamagnetic and therefore multinuclear solution NMR studies can be performed, which 

is of major importance for medicinal applications. The fact that all tungsten centers are 

in the fully oxidized +6 state also allows for unequivocal determination of the charges of 

the product polyanions. 

68

Part-II 

Mono-Organo Tin POMs

3.6 The bis-phenyltin substituted, lone pair containing 

tungstoarsenate: 

({C 6 H 5 Sn} 2 As 2 W 19 O 67 (H 2 O)) 8− 


The precursor K 14 [As 2 W 19 O 67 (H 2 O)] was synthesized according to the published procedure 

of Kortz et al. and the purity was confirmed by infrared spectroscopy [33]. All other 

reagents were used as purchased without further purification. (NH 4 ) 7 Na[(C 6 H 5 Sn) 2 As 2 W 19 

O 67 (H 2 O)]·17.5H 2 O (NH4-8). The title compound was synthesized by dissolving 0.145 

mL (0.88 mmols) of C 6 H 5 SnCl 3 in 40 mL H 2 O followed by addition of 2.10 g (0.40 mmols) 

K 14 [As 2 W 19 O 67 (H 2 O)]. This solution (pH 1.6) was heated to 80 ∼ 80 ◦ C for 1 h and then 

cooled to room temperature. The solution was filtered and a few drops of 0.1 M NH 4 Cl 

and 0.1 M NaCl solution were added and then the solution was allowed to evaporate in 

an open vial at room temperature. A white crystalline product started to appear after a 

week. Evaporation was continued until the solvent approached the solid product (yield 

1.6 g, 72%). FTIR spectra for (NH 4 ) 7 Na[(C 6 H 5 Sn) 2 As 2 W 19 O 67 (H 2 O)]·17.5H 2 O: 964(m), 

905(m), 881(m), 860(m), 801(sh), 754(s), 736(s), 702(sh), 582(w), 518(sh), 486(w), 446(w) 

cm −1 . Anal. Calcd (Found) for (NH 4 ) 7 Na[(C 6 H 5 Sn) 2 As 2 W 19 O 67 (H 2 O)]·17.5H 2 O: N 1.8 

(1.6), Na 0.4 (0.2), Sn 4.2 (4.3), W 62.4 (61.6), As 2.7 (2.7), C 2.6 (2.7), H 1.6 (1.5). NMR 

spectroscopy of 8 at pH 1.6 (D 2 O, 293 K): 183 W: -110.5, -120.7, -150.0, -159.6, -170.5, 

-196.9 ppm (all singlets with intensities 4:2:4:4:4:1); 119 SnH: -432.5 ppm (singlet); 13 CH: 

129.7, 132.0, 133.6, 137.3 ppm (singlets); 1 H: 7.6, 8.1 ppm (multiplets). Monophenyltrichloride 

(C 6 H 5 SnCl 3 ) in H 2 O at pH 1.6, 119 SnH: -536.5 ppm (singlet); 13 CH: 128.9, 

130.4, 133.1, 134.3 ppm (singlets); 1H: 7.3, 7.5 ppm (multiplets). Elemental analysis 

was performed by Kanti Labs Ltd. in Mississauga, Canada. The FTIR spectrum was 

recorded on a Nicolet Avatar FTIR spectrophotometer in a KBr pellet. All NMR spectra 

were recorded on a JEOL Eclipse 400 instrument at room temperature using D 2 O as a 

solvent. 

70

Fig. 3.32: FTIR spectra of compound NH4-8(red) and K 14 [As 2 W 19 O 67 (H 2 O)](blue) 


A crystal of compound NH4-8 was mounted on a glass fiber for indexing and intensity 

data collection at 163 K on a Bruker D8 SMART APEX CCD single-crystal diffractometer 

using Mo K radiation ( λ = 0.71073 Å). Direct methods were used to solve the structure 






The novel bis-phenyltin substituted, dimeric tungstoarsenate(III) [(C 6 H 5 Sn) 2 As 2 W 19 O 67 

(H 2 O)] 8− (6) consists of two lacunary B-α-[AsW 9 O 33 ] 9− Keggin fragments linked via 

two (C 6 H 5 Sn) 3+ groups and a WO(H 2 O) 4+ moiety leading to a structure with nominal 

C 2v symmetry (see Figure 3.33). Alternatively 8 can be described as a dilacunary 

[As 2 W 19 O 67 (H 2 O)] 14− fragment which has taken up two organotin units. It can be noticed 

that the tin atoms are situated well above the plane of the four equatorial 2-oxo 

ligands. Therefore the tin atoms are displaced towards the terminal phenyl ligand, i.e. 

71

Table 3.7: Crystal Data and Structure Refinement for compound NH4-8 

Emperical formula As 2 C 12 H 75 N 7 NaO 85 .5Sn 2 W 19 

fw 5594.1 


a (Å) 18.3127(17) 

b (Å) 24.403(2) 

c (Å) 22.965(2) 

vol (Å 3 ) 9854.0(16) 

Z 4 

temp ( ◦ C) -110 


d calcd (mg m −3 ) 3.73 

abs coeff. (mm −1 ) 23.354 

R [I > 2 σ(I)] a 0.075 



Fig. 3.33: Combined polyhedron and ball/stick representations of [(C 6 H 5 Sn) 2 As 2 W 19 O 67 

(H 2 O)] 8− (left),Top view (right) 

towards the exterior of the equator of 8. This resembles the displacement of all tungsten 

sites of 8 towards the external, terminal oxo groups. On the other hand, the unique tungsten 

atom in the central belt of 8 is displaced towards the interior of the equator of 8. As 

a result of this symmetry breaking, polyanion 8 exhibits a surface with both positive and 

negative curvature. Bond-valence-sum (BVS) calculations for 8 indicated that no oxygen 

72

of the two (AsW 9 O 33 ) caps is protonated [85]. However, the central tungsten atom has 

two trans related ligands which are a water molecule and an oxo group. The latter is 

inside the central cavity of 8 whereas the former is on the outside. This is in complete 

agreement with the single-crystal XRD data of related structures that contain one or three 

central tungsten atoms linking two (α-AsW 9 O 33 ) fragments (e.g. [As 2 W 19 O 67 (H 2 O)] 14− , 

[As 2 W 21 O 69 (H 2 O)] 6− ) [33]. The title polyanion 8 was synthesized rationally and in a 

one-pot reaction by interaction of C 6 H 5 SnCl 3 with K 14 [As 2 W 19 O 67 (H 2 O)] in aqueous, 

acidic medium (pH 2). However, we obtained 8 for the first time accidentally during 

our efforts to discover novel diphenyltin substituted species. Interaction of (C 6 H 5 ) 2 SnCl 2 

with Na 9 [α-AsW 9 O 33 ] and Na 2 WO 4 in a molar ratio of 3:1:3 in aqueous medium at pH 

2 resulted in 8. This means that the diphenyltin precursor underwent partial hydrolysis 

resulting in the loss of one phenyl group. Then we decided to reproduce this compound 

via a more rational synthetic procedure using the dilacunary polyoxotungstate precursor 

[As 2 W 19 O 67 (H 2 O)] 14− and (C 6 H 5 )SnCl 3 (see Experimental section). The tungstoarsenate 

[As 2 W 19 O 67 (H 2 O)] 14− was synthesized for the first time about 30 years ago by Tourné 

et al. and recently Kortz et al. confirmed the proposed structure by X-ray diffraction 

[33, 128, 129]. Interestingly, to date only a few polyoxoanions have been synthesized 

using [As 2 W 19 O 67 (H 2 O)] 14− as a precursor [33, 130, 131]. Polyanion 8 represents 

a novel member in the class of monoorganotin substituted polyoxotungstates in general 

and the subclass of tungstoarsenates(III) in particular. Pope et al. have synthesized 

and characterized several monomeric and dimeric polyoxotungstates substituted by 

monoorganotin functions [44–46, 132]. Amongst them the tetrakis(monophenyltin) substituted 

tungstoarsenate(III) [(C 6 H 5 Sn) 2 O 2 H(α-AsW 9 O 33 ) 2 ] 9− and the tris(monophenyltin) 

substituted tungstoantimonate(III) [(C 6 H 5 Sn) 3 Na 3 (H 2 O) 6 (α-SbW 9 O 33 ) 2 ] 6− are related to 

8 [47]. These species were synthesized by reaction of C 6 H 5 SnCl 3 with Na 9 [α-AsW 9 O 33 ] 

and Na 9 [α-SbW 9 O 33 ], respectively, in aqueous acidic medium (pH 2). The antimony 

derivative [(C 6 H 5 Sn) 3 Na 3 (H 2 O) 6 (α -SbW 9 O 33 ) 2 ] 6− and 8 exhibit both a dimeric sandwich 

type structure with square pyramidal organotin groups, whereas [(C 6 H 5 Sn) 2 O 2 H(α- 

AsW 9 O 33 ) 2 ] 9− contains four monoorganotin units which are all octahedral. The solid state 

structure of NH4-8 indicates that the title polyanion contains a sodium atom in the cen- 

73

tral belt in-between the two tin atoms (dNa···Sn = 3.52 - 3.55(1) Å, see Figure 3.33). 

The sodium ion is six-coordinated by four bridging oxo-groups of 8 and two terminal 

water molecules resulting in an octahedral coordination sphere and typical bond lengths 

(dNa-O = 2.29 - 2.46(2) Å). The presence of a sodium ion in the belt of 8 is not all that 

surprising, as crystal structures of several derivatives of 8 have also revealed the presence 

of sodium ions in analogous positions. In[(C 6 H 5 Sn) 3 Na 3 (H 2 O) 6 ( α-SbW 9 O 33 ) 2 ] 6− three 

sodium ions are located in the central belt in addition to the three [C 6 H 5 Sn] 3+ groups 

[47]. This is analogous to the di- and tri-transition metal substituted derivatives of this 

structural type, [M 2 (H 2 O) 2 WO(H 2 O)Na 3 (H 2 O) 6 ( α-AsW 9 O 33 ) 2 ] 7− (M = Co 2+ , Zn 2+ ) and 

[M 3 (H 2 O) 3 Na 3 (H 2 O) 6 (α-XW 9 O 33 ) 2 ] 9− (X = As III , M = Mn 2+ , Co 2+ , Cu 2+ , Zn 2+ ; X = 

Sb III , M = Cu 2+ , Zn 2+ ) [39, 133]. The -8 charge of the polyanion is balanced by the unique 

sodium ion in the belt of 8 and seven ammonium ions which surround the polyanion. The 

exact positions of the ammonium ions could not be identified by X-ray diffraction as they 

could not be distinguished from water molecules. However, the result of elemental analysis 

is in complete agreement with the formula of NH4-8. The solid state arrangement of 

8 deserves special attention (see Figure 3.34). The title polyanions exhibit 2-D packing in 

Fig. 3.34: Projection of the crystal packing on the bc plane showing the 2-D arrangement of compound 8 

the bc plane and additional intermolecular connectivities in the c direction via W-O-Na 

bonds lead to the formation of chains. Interestingly the phenyl rings of adjacent polyanions 

interact in an orthogonal fashion. Nevertheless, the respective Na-O-W bond lengths 

74

(Na1-O12T = 2.401(14) Å; W12-O12T = 1.698(13) Å) indicate that this intermolecular 

interaction is rather weak and mostly a result of crystal packing. It can be expected that 

redissolution of NH4-8 leads to a complete breakdown of the entire lattice, resulting in 

the presence of individual polyanions 8 in solution. In order to verify this assumption we 

decided to perform multinuclear NMR spectroscopy. 

Solution NMR 

Polyanion 8 is diamagnetic and contains four spin 1/2 nuclei ( 183 W, 119 Sn, 13 C, 1 H) and 


The 1 H and 13 C-NMR spectra of 8 are consistent with two equivalent phenyl groups. 

Especially 183 W-NMR is a very sensitive technique which allows to verify if the solid state 

structure of a polyoxotungstate is preserved in solution. However, the low natural abundance 

of the 183 W-nucleus requires preparation of very concentrated solutions. In order 

to accomplish this we synthesized 8 as described in the Experimental section but with 

a four times higher concentration. During the reaction solid LiClO 4 was added in order 

to prevent precipitation of 8. The solid KClO 4 was filtered off before running the NMR 

measurements, which means that essentially all potassium ions were removed from the 

solution. Therefore the only remaining cations in the solution of 8 studied by NMR were 

NH 4+ and Li + . For 8 a six line pattern with relative intensities 4:4:4:4:2:1 is expected 

and indeed this is what we observed, confirming the C 2v symmetry of 8 (see Figure 3.33). 

This conclusion is based on the assumption that the two phenyl groups can rotate freely 

in solution, which is most likely the case. The smallest peak in the 183 W-NMR spectrum 

( -196.9 ppm) is somewhat hard to be identified, but we performed several experiments 

to confirm our assignment. The 119 Sn-NMR spectrum of 1 is expected to show a single 

peak, if the two Sn atoms are equivalent. Indeed a single resonance at -432.5 ppm is 

observed, but in addition we see a pair of fairly intense satellites which most likely result 

from coupling of a 119 Sn nucleus to an adjacent 183 W nucleus (see Figure 3.34). Pope et 

al. observed a singlet in 119 Sn-NMR for [(C 6 H 5 Sn) 3 Na 3 (H 2 O) 6 (α-SbW 9 O 33 ) 2 ] 6− of almost 

identical chemical shift (-417.8 ppm) to 8 and a pair of satellites with similar intensity.[47] 

In his polyanion the tin atoms are in a square-pyramidal coordination geometry, in com- 

75

Fig. 3.35: 183 W NMR spectra of compound 8 

Fig. 3.36: 119 Sn NMR spectra of compound 8 

plete analogy to 8. Although single-crystal X-ray diffraction of NH4-8 clearly indicated 

the presence of a sodium ion in the central belt of the title polyanion, it must be remembered 

that we synthesized 8 in the absence of sodium ions (see Experimental section). 

Furthermore we eliminated the potassium ions by precipitation as KClO 4 as described 

above. Sodium ions were only added after the synthesis of 8 in order to obtain better 

quality crystals. Based on our observation that in the solid state structure a sodium ion 

is located in the central belt of 8, we decided to investigate by 119 Sn-NMR if sodium ions 

also play an important role in solution. We discovered that in the absence of sodium ions 

only one signal is observed at -432.5 ppm together with a pair of satellites (see Figure 

3.36. Addition of solid NaCl to this solution or alternatively the presence of sodium ions 

already during the synthesis of 8 resulted in both cases in the appearance of a second 

76

119 Sn-NMR signal at -434.9 ppm with the expected pair of satellites (2JSn-W = 100 Hz). 

This peak increased with the concentration of sodium ions in solution, but never reached 

the same intensity as the -432.5 ppm peak. Our conclusion is that the peak at -434.9 ppm 

almost certainly represents 8 with a sodium ion in the vacancy. We could not identify any 

two-bond 119 Sn- 23 Na coupling in this peak pattern, most likely for the following reasons: 

(a) the 23 Na nucleus is quadrupolar (I = 3/2) and the satellite signal would be a quartet, 

(b) the Na-O bond lengths are rather long (2.44 - 2.46(2) Å) so that any coupling would 

be expected to be rather weak. On the other hand we believe that the peak at -432.5 ppm 

indicates a vacancy in the title polyanion 8 in-between the two tin atoms. The fact that 

the 119 Sn-NMR signal for the sodium-substituted species at -434.9 ppm is always smaller 

than the signal at -432.5 ppm (even for high Na + concentrations) indicates that the latter 

represents almost certainly a species with a ‘vacant’ belt. The two freely rotating phenyl 

groups probably exhibit a steric effect which makes incorporation of an alkali cation in the 

belt of 8 more difficult. We also performed 23 Na-NMR on solutions of 8 with added sodium 

chloride. For such solutions a single peak is observed at around -1.5 ppm, which is very 

similar to the chemical shift of our 1 M NaCl reference solution. No satellite peaks could 

be observed, but we noticed that the peak of the polyanion solution is significantly broader 

than that of the NaCl reference solution. This could be a result of exchange-broadening, 

which appears to be fast on the NMR timescale. The observed Sn-O-W coupling constant 

for 8 (2JSn-W = 96 Hz) is even larger than the largest values reported by Pope et al. for 

[(C 6 H 5 Sn) 3 P 2 W 15 O 59 ] 9− ( 2 JSn-W = 78 Hz), [(C 4 H 9 Sn) 3 P 2 W 15 O 59 ] 9− ( 2 JSn-W = 49 Hz), 

[(C 6 H 5 SnOH) 3 ( α-SiW 9 O 34 ) 2 ] 14− ( 2 JSn-W = 35 Hz) and [(C 6 H 5 SnOH) 3 (PW 9 O 34 ) 2 ] 12− 

( 2 JSn-W = 33 Hz). Pope et al. have identified that an increase in the Sn-O-W bond angle 

is accompanied by an increasing Sn-O-W coupling constant for [(C 6 H 5 Sn) 3 P 2 W 15 O 59 ] 9− 

( 2 JSn-W = 78 Hz, Sn-O-W = 147-158 ◦ ) and [(C 6 H 5 SnOH) 3 (PW 9 O 34 ) 2 ] 12− ( 2 JSn-W 

= 33 Hz, Sn-O-W = 139-142 ◦ ).[44] However, this bond angle argument alone does 

not explain the very large coupling constant observed for 8, as the Sn-O-W bond angle 

ranges from 135.0-139.6 ◦ . Most likely the coordination geometries of the tin atoms 

play also an important role. In all of Popes polyanions above (with the exception of 

[(C 6 H 5 Sn) 3 Na 3 (H 2 O) 6 (α-SbW 9 O 33 ) 2 ]6−) the Sn atoms are six-coordinated (octahedral), 

77

whereas they are five-coordinated (square-pyramidal) in 8. Perhaps the overall charge of 

the polyanion also affects the Sn-O-W coupling constant. It can be noticed that 8 has 

the smallest charge (-8) and the largest Sn-O-W coupling constant ( 2 JSn-W = 96 Hz). 

For Popes polyanions above the species with large negative charges have smaller coupling 

constants than those with smaller charges (e.g. [(C 6 H 5 Sn) 3 P 2 W 15 O 59 ] 9− , 2JSn-W = 78 

Hz vs. [(C 6 H 5 SnOH) 3 (α -SiW 9 O 34 ) 2 ] 14− , 2 JSn-W = 35 Hz). Nevertheless, NMR data of 

more polyanions containing square pyramidal organotin groups are needed in order to be 

able to draw definitive conclusions. The 183 W-, 119 Sn-, 13 C- and 1 H-NMR spectra of 8 remain 

the same even if the same solution is measured again after several weeks, indicating 

that 8 does not undergo structural transformations in aqueous acidic medium. 


We have synthesized the bis-phenyltin substituted, lone pair containing tungstoarsenate 

[(C 6 H 5 Sn) 2 As 2 W 19 O 67 (H 2 O)] 8− 8. Polyanion 6 was characterized by several solution 

(multinuclear NMR spectroscopy) and solid state (FTIR spectroscopy, elemental analysis, 

single-crystal XRD) techniques. This polyanion adds a new member to the class of 

monophenyltin substituted polyoyotungstates. Our work reemphasizes (a) the facile synthesis 

of polyoxoanions by one-pot reactions, (b) the structural variety of polyoxoanion 

chemistry, (c) the stability of polyoxoanions in solution, (d) the complementary nature 

of XRD and multinuclear NMR, (e) easy incorporation of monoorganotin fragments in 

polyoxotungstate precursors, (f) the strong attachment of organotin fragments to polyoxoanions. 

Nevertheless the work of Pope and also our work shows that interaction of 

monoorganotin groups with lacunary polyoxoanions almost inevitably leads to monomeric 

or dimeric products. Currently we investigate the reactivity of diorganotin groups with 

lacunary polyoxotungstates in order to synthesize discrete polyoxometalates with fundamentally 

novel architectures of large size. 

78

3.7 Conclusions and Outlook 

3.7.1 Conclusion 

The primary objective of this work was to synthesize novel discrete polyoxometalates 

(POMs) functionalized by diorganotin groups. Diorganotin electrophiles were reacted with 

a variety of lacunary POM precursors (ligands) in aqueous media over a wide range of synthetic 

conditions. Novel discrete POMs species as monomers, dimers, trimers, tetramers 

and dodecamers were synthesized and structurally characterized by FTIR, single crystal 

X-ray diffraction, multinuclear NMR, electrochemistry (Dr. B. Keita, and Prof. L. Nadjo, 

(Université Paris-Sud, Orsay Cedex, France), scanning tunneling microscopy ( Prof. P. 

Müller and his coworkers Mr. M. S. Alam, V. Dremov, Physikalisches Institut III, (Universität 

Erlangen-Nürnberg, Germany). From our observations it can be concluded that: 

(i)The dimethyltin unit (CH 3 ) 2 Sn 2+ is a reactive electrophile and interacts readily with 

lacunary polyoxotungstates, such as the trilacunary [P V W 9 O 34 ] 9− and [As V W 9 O 34 ] 9− 

or the trilacunary, lone pair containing [As III W 9 O 33 ] 9− and [Sb III W 9 O 33 ] 9− . (ii) The 

dimethyltin unit (CH 3 ) 2 Sn 2+ is grafted exclusively at lacunary sites of polyanions, predominantly 

via two Sn-O(W) bonds. (iii) The methyl groups of the dimethyltin-containing 

POMs are trans to each other and therefore the (CH 3 ) 2 Sn 2+ group is an effective linker of 

POM precursors, resulting in large, open cage type structures. (iv) In most dimethyltincontaining 

POMs the tin atom exihibits coordination number six (octahedral) but in the 

tetrameric polyanion 5 ([{Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }As 3 (α-AsW 9 O 33 ) 4 ] 12− ) coordination 

number seven (pentagonal bipyramidal) was observed. (v) The Sn-C bond lengths 

in in dimethyltin-containing POMs range from 1.9 - 2.1 Å. (vi) The C-Sn-C bond angles 

in dimethyltin-containing POMs range from 150 - 175 ◦ . (vii) The dimethyltin-containing 

POM structures are open and exhibit central cavities and/or surface pockets which may 

allow for host-guest chemistry.. (viii) The diamagnetic nature of dimethyltin-containing 

POMs allows for multinuclear solution NMR (e.g. 119 Sn, 183 W, 13 C, 1 H). (ix) In a collaboration 

with the group of Prof. P. Müller (Physikalisches Institut III, Universität 

Erlangen-Nürnberg, Germany) the dodecameric 6 ([{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A- 

PW 9 O 34 ) 12 ] 36− ) was deposited on highly oriented pyrolitic graphite (HOPG) and then 

79

investigated by scanning tunneling microscopy (STM) Individual polyanions could be visualized. 

(x) In a collaboration with the group of Prof. L. Nadjo and Dr. B. Keita (Université 

Paris-Sud, Orsay Cedex, France) detailed electrochemistry studies were carried 

out on our dimethyltin-containing POMs. This work usually involved cyclic voltammetry 

studies. (xi) Reaction of (C 6 H 5 ) 2 Sn 2+ with lacunary tungstoarsenates(III) in aqueous 

acidic medium and heating resulted in partial hydrolysis of the former. Loss of one phenyl 

group resulted in formation of monophenyltin-POMs. 

3.7.2 Outlook 

The reactivity of (C 6 H 5 ) 2 Sn 2+ can be further investigated by using other lacunary POMs 

including borotungstates (e.g.[B 3 W 39 O 132 ] 21− ), arsenotungstates (e.g. [As 2 W 19 O 67 (H 2 O)] 14− , 

[As 2 W 20 O 68 (H 2 O)] 10− ), silicotungstates (e.g. [γ-SiW 10 O 36 ] 8− , [SiW 9 O 34 ] 10− ), germanotungstates 

(e.g. [γ-GeW 10 O 36 ] 8− , [GeW 9 O 34 ] 10− ) and perhaps also mixed polyoxotungstate 

ligands. In is also of interest to study the reactivity of the diethyltin group (C 2 H 5 ) 2 Sn 2+ 

with a variety of POM precursors. Such POM derivatives might allow for further derivatization 

of the alkyl chain leading to peptides, thiols etc. The interaction of these species 

with enzymes and other biomolecules can also be studied and might allow for a better 

understanding of the antitumor/-viral activities of this class of compounds. Moreover, 

such derivatized POMs may also be used for stabilizing nanoparticles. Finally, it can also 

be envisaged to extend the diorganotin-POM work to the lighter homologue diorganogermanium 

R 2 Ge 2+ 80

Part-III 

Titanium Containing POMs

3.8 The di-titanium substituted, lone pair containing 

tungstoarsenate: 

{(TiOH) 2 WO(H 2 O)(B-α-AsW 9 O 33 ) 2 } 8− 

3.8.1 Introduction 

Polyoxometalates (POMs) are an important class of inorganic compounds and they exhibit 

a diverse compositional range and significant structural versatility [1, 134]. POMs 

are usually composed of early transition metal MO 6 (M = W 6+ , Mo 6+ etc.) octahedra 

and main group XO 4 (X = P, Si etc.) tetrahedra. The most famous POMs are probably 

the Keggin (e.g. (PW 12 O 40 ) 3− ) and the Wells-Dawson (e.g. (P 2 W 18 O 62 ) 6− ) ions. Nevertheless, 

also lone pair containing main group elements (e.g. As III ) can act as hetero 

groups. There are numerous uses of POMs utilizing their specific molecular composition, 

size, shape, charge density, redox potentials, acidity and solubility characteristics, which 

span a wide range of applications including homogeneous and heterogeneous catalysts, 

electro-catalysts, coatings, medicinal agents, pigments, recording materials, toners, precursors 

for oxide films, sensors and nano/biotechnology [2–5, 135]. POMs have received 

particular attention in environmentally benign catalytic processes and in antiviral and 

antitumoral chemotherapy [2–5, 135]. Nevertheless the structure/composition-activity 

relationship of POMs in these and other applications is not yet fully understood and 

therefore the synthesis of new types of such polyanions remains an important research 

objective. Catalytic activity (e.g. activation of O 2 and H 2 O 2 ) combined with high thermal 

stability have led to industrial applications of these species, mostly as heterogeneous 

catalysts in the oxidation of organic substrates (e.g. Wacker process) [2–5, 135]. Titanium 

substituted polyoxoanions are of interest for structural reasons as well as for their 

universal catalytic properties. Polyoxometalates substituted with early transition metal 

d 0 ions such as vanadium (V) and niobium (V) in a fully oxidized state increases the 

basicity of the polyanions, which may enable the binding of organometallic fragments to 

specific sites of the anion, or even the functionalization of Ir nanoclusters to the polyanions, 

which is well documented [136–145]. Substitution of V V and Nb V by Ti IV ions 

82

should even lead to a more pronounced effect. Indeed it has been observed that titanium 

atoms incorporated in polyoxoanions are reactive sites with a strong tendency to form 

dimers through Ti-O-Ti bonds as seen in [(α-Ti 3 PW 9 O 38.5 ) 2 ] 12− , [(x-Ti 3 SiW 9 O 38.5 ) 2 ] 14− 

(x =α,β), [(α-Ti 3 GeW 9 O 38.5 ) 2 ] 14− , [(α-1,2-Ti 2 PW 10 O 39 ) 2 ] 10− , and [(β-Ti 2 SiW 10 O 39 ) 4 ] 24− 

[146–151]. Nevertheless, two monomeric species have also been structurally characterized 

[152–155]. Interestingly all these monomeric, dimeric and cyclic tetrameric species are 

polyoxotungstates based on the Keggin structure as a basic building framework. Some of 

the above species have shown interesting catalytic (e.g. photocatalysis) as well as medicinal 

activity (e.g. antiviral) [156–162]. The search for novel transition-metal substituted 

polyanions is predominantly driven by their catalytic properties. Our group have been 

interested in Ti-substituted polyoxometalates for a few years mainly because of their attractive 

properties like catalysis and photocatalysis. Kortz et al. reported that interaction 

of titanium(IV) with the Wells-Dawson ion [P 2 W 15 O 56 ] 12− in aqueous solution can lead 

to a variety of products with unexpected, supramolecular structures [163]. Soon after 

similar work was also reported by Nomiya et al. but they were unsuccessful to obtain 

single crystal suitable for X-ray diffraction [164, 165]. Here we report on the structural 

characterization of titanium(IV)-substituted polyoxoanions of the lone pair containing 

dilacunary tungstoarsenate(III) [As 2 W 19 O 67 (H 2 O)] 14− . 


The precursor K 14 [As 2 W 19 O 67 (H 2 O)] was synthesized according to the published procedure 

of Kortz et al. and the purity was confirmed by infrared spectroscopy [33]. All other 

reagents were used as purchased without further purification. Cs 8 [(TiOH) 2 As 2 W 19 O 67 (H 2 O)] 

·10.5 H 2 O (Cs-9). The title compound was synthesized by dissolving 0.141 g (0.88 mmols) 

of TiO(SO 4 ) in 40 mL H 2 O, followed by addition of 2.10 g (0.40 mmols) K 14 [As 2 W 19 O 67 (H 2 O)]. 

This solution (pH 2.0) was heated to ∼80 ◦ C for 1 h and then cooled to room temperature. 

The solution was filtered and a few drops of 0.1 M CsCl solution were added and then the 

solution was allowed to evaporate in an open vial at room temperature. A light yellow 

crystalline product started to appear after a week or two. Evaporation was continued 

until the solvent approached the solid product (yield 1.43 g, 63.8 %). FTIR spectra for 

83

Fig. 3.37: Ball/stick (left), polyhedral (right) representations of 9 

Cs 8 [(TiOH) 2 As 2 W 19 O 67 (H 2 O)]·10.5 H 2 O: 963(s), 898(s), 761(s), 712(s), 589(sh), 484(w), 

448(w) cm −1 . The FTIR spectrum was recorded on a Nicolet Avatar FTIR spectrophotometer 

in a KBr pellet. 


A crystal of compound Cs-9 was mounted on a glass fiber for indexing and intensity data 







84

Table 3.8: Crystal Data and Structure Refinement for compound Cs-9 

Empirical formula As 2 Cl 2 Cs 8.5 O 78.5 Ti 2 W 19 

fw 6195.42 

space group P 2 1 /m (11) 

a (Å) 12.776(19) 

b (Å) 19.425(3) 

c (Å) 18.149(3) 

β ( ◦ ) 110.23(3) 

vol (Å 3 ) 4226(5) 

Z 2 

temp. ( ◦ C) -100 


d calc (mg m −3 ) 4.868 

abs. coeff. (mm −1 ) 30.466 

R [I > 2 σ(I)] a 0.081 





The novel di-titanium substituted, dilacunary tungstoarsenate(III) [(TiOH) 2 As 2 W 19 O 67 (H 2 O)] 8− 

9 consists of two lacunary B-α-[AsW 9 O 33 ] 9− Keggin fragments linked via two Ti(IV) 

atoms and a {WO(H 2 O)} 4+ moiety leading to a structure with nominal C 2 v symmetry 

(see Figure 3.37). Alternatively 9 can be described as a dilacunary [As 2 W 19 O 67 (H 2 O)] 14− 

fragment which has taken up two Ti(IV) units. It can be noticed that the titanium atoms 

are situated well above the plane of the four equatorial oxo ligands. Therefore the titanium 

atoms are displaced towards the exterior of the equator of 9. This resembles the 

displacement of all tungsten sites of 9 towards the external, terminal oxo groups. On 

the other hand, the unique tungsten atom in the central belt of 9 is displaced towards 

the interior of the equator of 9. Bond-valence-sum (BVS) calculations for 9 indicated 

that no oxygen of the two (AsW 9 O 33 ) caps is protonated [85]. However, the central tungsten 

atom has two trans related ligands which are a water molecule and an oxo group. 

The latter is inside the central cavity of 9 whereas the former is on the outside. This 

is in complete agreement with the single-crystal XRD data of related structures that 

contain one or three central tungsten atoms linking two ( α-AsW 9 O 33 ) fragments (e.g. 

85

[As 2 W 19 O 67 (H 2 O)] 14− , [As 2 W 21 O 69 (H 2 O)] 6− ) [33, 35, 129]. The title polyanion 9 was 

synthesized rationally and in a one-pot reaction by interaction of titanium oxosulphate 

TiO(SO 4 ) with K 14 [As 2 W 19 O 67 (H 2 O)] in aqueous, acidic medium (pH 2.0). However, we 

obtained 9 for the first time accidentally during our efforts to discover novel titanium 

substituted sandwich type species. Interaction of TiO(SO 4 ) with Na 9 [B-AsW 9 O 33 ] in 

a molar ratio of 4:1 in aqueous medium at pH 4.0 resulted in 9. Then we decided to 

reproduce this compound via a more rational synthetic procedure using the dilacunary 

polyoxotungstate precursor [As 2 W 19 O 67 (H 2 O)] 14− and TiO(SO 4 ) (see Experimental Section). 

The tungstoarsenate [As 2 W 19 O 67 (H 2 O)] 14− was synthesized for the first time about 

30 years ago by Tourné et al. and recently Kortz et al. confirmed the proposed structure 

by X-ray diffraction [33, 128, 129]. Interestingly, to date only a few polyoxoanions have 

been synthesized using [As 2 W 19 O 67 (H 2 O)] 14− as a precursor [33, 130, 131]. Polyanion 

9 represents a novel member in the class of titanium substituted polyoxotungstates in 

general and the subclass of tungstoarsenates(III) in particular. Recently, our group reacted 

(C 6 H 5 ) 2 SnCl 2 with [As III 2W 19 O 67 (H 2 O)] 14− in aqueous medium at pH 1.6, resulting 

in novel bis-phenyltin substituted species, [Na(H 2 O)(C 6 H 5 Sn) 2 As III 2W 19 O 67 (H 2 O)] 7− 

[166]. Most recently our group interacted Pd 2+ ions with the lacunary Keggin precursors 

A-α-[SiW 9 O 34 ] 10− in buffer solutions (pH 4.9) resulting in novel structurally characterized 

palladium substituted species. [Pd 2 WO(H 2 O)(A-α-SiW 9 O 34 ) 2 ] [167]. Therefore, the 

mechanism of formation of 9 involves insertion and isomerization (B-alpha-[AsW 9 O 33 ] 9− 

→ [As III 2W 19 O 67 (H 2 O)] 14− ). Most interestingly, the central As III atoms in 

[As III 2W 19 O 67 (H 2 O)] 14− have lone pairs of electrons but in the later case the central hetero 

atoms Si IV do not contain lone pairs of electrons. So, this tungsten-oxo fragment for 

silicotungstates [Si 2 W 19 O 69 (H 2 O)] 16− has never been observed before and therefore it represents 

the first 2:19 series of silicotungstate containing central hetero atoms without lone 

pairs of electrons. But such 2:19 series of phosphotungstates are known for two decades 

where the heteroatom do not contain lone pair of electrons.[80] Currently, our group is 

engaged in isolating the novel silicotungstate assembly [Si 2 W 19 O 69 (H 2 O)] 16− in a more 

rational way. The mechanism of formation of polyoxometalates is not well understood 

and commonly described as self-assembly. Therefore, the design of novel polyoxometa- 

86

lates remains a challenge for synthetic chemists. This is analogous to the di-transition 

metal substituted derivatives of this structural type, [M 2 (H 2 O) 2 WO(H 2 O)Na 3 (H 2 O) 6 (α 

-AsW 9 O 33 ) 2 ] 7− (M = Co 2+ , Zn 2+ ) [39]. The two titanium cations are bound to two “terminal” 

oxygen atoms of pairs of edge-shared WO 6 octahedra of each B-α-[AsW 9 O 33 ] 9− anion 

of the dimer. Both the titanium atoms display square pyramidal geometry. Bond-valencesum 

(BVS) calculations show that both titanium are coordinated axially to -OH ligands. 

The Ti-O bond lengths (1.964-1.985 Å) and the O-Ti-O angles (84-85 ◦ , 159-159.5 ◦ ) are 

very close to that of nominal values. Ti1···Ti2, Ti1···W19 and Ti2···W19 distances in 9 

are 5.1, 4.6 and 4.6 Å, respectively. These values indicate that two Ti and a W in the 

central belt of polyanion 9 form an approximate isosceles triangle. The -8 charge of the 

title polyanion is balanced by eight cesium ions which surround the polyanion. The exact 

positions of all the cesium ions could not be identified by X-ray diffraction. However, the 

result of elemental analysis is in complete agreement with the formula of Cs-9. 


We have synthesized the di-titanium substituted, lone pair containing tungstoarsenate 

[(TiOH) 2 As 2 W 19 O 67 (H 2 O)] 8− 9. Polyanion 9 was characterized in the solid state by 

different analytical techniques like FTIR spectroscopy, elemental analysis, single-crystal 

XRD. This polyanion adds a new member to the class of titanium substituted polyoyotungstates. 

Our work reemphasizes (a) the facile synthesis of polyoxoanions by one-pot 

reactions, (b) the structural variety of polyoxoanion chemistry, (c) the first example where 

the polyoxometalates dimerizes without formation of Ti-O-Ti bond in low pH. (d) adds 

to the subclass where Keggin fragment is used as building blocks (e) easy incorporation 

of titanium(IV) in lone pair containing tungstatoarsenate precursors. Currently we 

are investigating the electro- and photochemical,electrocatalytic, and oxidation catalysis 

properties of 9 and this work is under investigation. 

(Manuscript in preparation) 

87

3.9 The cyclic trimeric-titanium substituted, 

tungstophosphate: [{Ti 3 O 4 (A-α-PW 9 O 34 )} 3 (PO 4 )] 13− 


The precursor K 14 [P 2 W 19 O 69 (H 2 O)] was synthesized according to the published procedure 

of Tourné et al. and the purity was confirmed by infrared spectroscopy [80]. All 

other reagents were used as purchased without further purification. Rb 9 K 4 [{(Ti 3 O 4 )(A-α- 

PW 9 O 34 )} 3 (PO 4 )]·18 H 2 O (RbK-10). The title compound was synthesized by dissolving 

0.141 g (0.88 mmols) of TiO(SO 4 ) in 40 mL potassium acetate buffer followed by addition 

of 2.26 g (0.40 mmols) K 14 [P 2 W 19 O 69 (H 2 O)]. This solution (pH 4.8) was heated to ∼80 

◦ C for 1 h and then cooled to room temperature. The solution was filtered and a few 

drops of 0.1 M RbCl solution were added and then the solution was allowed to evaporate 

in an open vial at room temperature. A white crystalline product started to appear after 

a week or two. Evaporation was continued until the solvent approached the solid product 

(yield 1.43 g, 63.8 %). FTIR spectra for Rb 9 K 4 [{(Ti 3 O 4 )(A-α-PW 9 O 34 )} 3 (PO 4 )]·18 H 2 O 

: 1163(sh), 1064(s), 1030(w), 959(s), 883(w), 788(s), 686(s), 588(w), 511(w) cm −1 . The 

FTIR spectrum was recorded on a Nicolet Avatar FTIR spectrophotometer in a KBr 

pellet. 

Fig. 3.38: FTIR spectra of compound RbK-10(red) and K 14 [P 2 W 19 O 69 (H 2 O)](blue) 

88


A crystal of compound RbK-10 was mounted on a glass fiber for indexing and intensity 

data collection at 173 K on a Bruker D8 SMART APEX CCD single-crystal diffractometer 






Fig. 3.39: Ball/stick and polyhedral representation of polyanion 10, color codes: blue polyhedra (W), 

yellow balls (Ti), red balls (O) and pink polyhedra (PO4) 

Results and discussion 

The novel polyanion 10 is composed of three [A-α-PW 9 O 34 ] units and nine TiO 6 octahedra. 

The nine TiO 6 octahedra are connected to each other by Ti-O-Ti bridges. Three 

TiO 6 octahedra of each trilacunary [A-α-PW 9 O 34 ] unit fills the lacuna to form a complete 

Keggin cluster. Of the three TiO 6 octahedra two are connected to Ti-centers of adjacent 

polyanions by Ti-O-Ti bridges, the unique TiO 6 octahedra in each Keggin subunit is connected 

to a phosphate ligand, which act as a capping tris monodentae fragment, leading 

to a discrete cyclic trimeric cluster. The polyanion has a nominal symmetry of C 3v (See 

89

Table 3.9: Crystal Data and Structure Refinement for compound RbK-10 

Empirical formula K 9 O 136 P 4 Rb 4 Ti 9 W 27 

fw 8388.71 


a (Å) 29.7444(7) 

c (Å) 13.6254(9) 

volume (Å 3 ) 10439.8(8) 

Z 3 

temp. ( ◦ C) -100 


dcalc (mg m −3 ) 4.003 

abs. coeff. (mm −1 ) 24.508 

R [I > 2 σ(I)] a 0.063 



Figure. 3.36) 

Further studies are on progress. 

3.10 Structural control on the nanomolecular scale: 

Self- assembly of the polyoxotungstate wheel 

({β-Ti 2 SiW 10 O 39 } 4 ) 24− 


The catalytic activity (e.g. activation of O 2 and H 2 O 2 )combined with high thermal stability 

have led to industrial applications of these species, mostly as heterogeneous catalysts 

in the oxidation of organic substrates (e.g. Wacker process) [3–5]. The redox-activity of 

titanium in the oxidation state +4 is well known and has led to numerous catalytic studies 

using TiO 2 as photocatalyst [168–170]. To date only a few titanium(IV)-substituted 

polyoxoanions have been synthesized and most of them are of the Keggin-type. Structural 

characterization in the solid state indicates a strong tendency towards dimer formation 

via Ti-O-Ti bonds as seen in [(α-Ti 3 PW 9 O 38.5 ) 2 ] 12− , [(x-Ti 3 SiW 9 O 38.5 ) 2 ] 14− (x = α, β), 

[(α-Ti 3 GeW 9 O 38.5 ) 2 ] 14− and [(α-1,2-Ti 2 PW 10 O 39 ) 2 ] 10− [146, 148–151]. Nevertheless two 

90

monomeric species have also been structurally characterized [152–155]. Some of the above 

species have shown interesting catalytic (e.g. photocatalysis) as well as medicinal activity 

(e.g. antiviral) [156–158, 162]. Recently some dimeric and tetrameric Ti-substituted 

polyoxotungstates based on the Wells-Dawson fragment have been structurally characterized 

by Kortz et al. [163]. Soon afterwards Nomiya et al. reported on similar tetrameric 

species [164, 165]. Our group has been working extensively on the interaction of the 

metastable, dilacunary tungstosilicate [γ-SiW 10 O 36 ] 8− with low-valent, first row transition 

metals [171–173]. Now we decided to investigate the system Ti 4+ /[γ- SiW 10 O 36 ] 8− in 

some detail. 


Preparation of K 24 [β-Ti 2 SiW 10 O 394 ]·50H 2 O (K-11): A 2.23 g (0.75 mmol) sample of 

K 8 [γ-SiW 10 O 36 ] was added with stirring to a solution of 0.26 g (1.65 mmol) TiO(SO 4 ) (E. 

Merck) in 40 mL H 2 O. The pH was adjusted to 2 by addition of 4 M HCl. This solution 

was heated to ∼80 ◦ C for 1 hour and then cooled to room temperature and filtered. Slow 

evaporation at room temperature resulted in a white, crystalline product after 2-3 weeks 

that was filtered off and air-dried. Yield: 1.39 g (61%). FTIR spectroscopy: 1000(w), 

966(m), 913(s), 803(s), 657(m), 541(w), 516(w), 487(w), 467(w) cm −1 . Anal. Calcd for 

K 24 -7: K, 7.7; W, 60.4; Ti, 3.1; Si, 0.9. Found: K, 7.3; W, 61.6; Ti, 2.8; Si, 1.2. Elemental 

analysis was performed by Kanti Labs Ltd. in Mississauga, Canada. 

Interaction of solid TiO(SO 4 ) with [γ-SiW 10 O 36 ] 8− in the ratio 2:1 in aqueous acidic 

medium (pH 2) resulted in the novel, tetrameric [β-Ti 2 SiW 10 O 394 ] 24− (7), see Figures 

3.41. 


A crystal of compound K-11 was mounted on a glass fiber for indexing and intensity data 





91

Fig. 3.40: FTIR spectra of compound K-11(red) and K 8 [γ-SiW 10 O 36 ](blue) 

Fig. 3.41: Polyhedral (left) and ball and stick (right) representations of({β-Ti 2 SiW 10 O 39 } 4 ) 24− . 



92

Table 3.10: Crystal Data and Structure Refinement for compound K-11 

Emperical formula H 100 K 24 O 206 Si 4 Ti 8 W 40 

fw 12184.9 

space group (No.) P 2 1 /n (14) 

a (Å) 12.5188(13) 

b (Å) 18.864(2) 

c (Å) 41.075(4) 

vol (Å 3 ) 9618.1(18) 

Z 2 

temp ( ◦ C) -100 


d calcd (mg m −3 ) 4.20 

abs coeff. (mm −1 ) 24.631 

R [I > 2 σ(I)] a 0.104 




Polyanion 11 represents the first cyclic, tetrameric polyoxotungstate and it is also the 

largest Ti-substituted tungstosilicate known to date. Bond valence sum calculations 

(BVS) indicate that 11 is not protonated and therefore its charge must be 24 [85]. This 

is fully consistent with elemental analysis, which indicated the presence of 24 potassium 

ions. Due to disorder we could identify only 17 potassium counterions by X-ray diffraction. 

The central cavity of the wheel-shaped 11 is occupied by a potassium cation and 

an additional two K + ions act as ‘wheel caps. The remaining potassium ions are wrapped 

all around 11 being coordinated to bridging and terminal oxo-groups of 11 as well water 

molecules of hydration. Polyanion 11 is composed of four (β-Ti 2 SiW 10 O 39 ) Keggin fragments 

that are linked via Ti-O-Ti bridges leading to a cyclic assembly. The only symmetry 

element of 11 is an inversion center, resulting in the point group C i . Close inspection of 

11 indicates that the four Keggin fragments are of the beta-type, which is rare and the 

first compound containing such a dilacunary tungstosilicate fragment was the dimeric, 

nickel-substituted polyanion [β- Ni 2 SiW 10 O 36 (OH) 2 (H 2 O) 2 ] 12− [173]. Therefore 11 constitutes 

only the second example composed of a beta-decatungstosilicate Keggin fragment 

and it represents the first tetrameric derivative. Interestingly the two titanium atoms of 

each beta- Keggin fragment are not located in the same M 3 O 13 triad. In fact they are 

93

Fig. 3.42: Side-view of compound 11 including the potassium ions (purple) inside the central cavity (K8) 

and above and below the cavity (K9, and K9’). 

separated by four bonds (Ti2-O-W3-O-Ti1 or Ti2-O-W8-O-Ti1, see Figure 3.41 (right)) 

and one of the two Ti atoms is located in the rotated triad (Ti2 and Ti4, see Figure 3.41). 

Based on the IUPAC nomenclature the two titanium atoms are located in positions 1 and 

10 (the latter being in the rotated triad) [2, 174]. In 11 each of the four Keggin fragments 

has a mirror plane and both titanium atoms are located in this plane of symmetry (see 

Figures 3.41). For comparison, the nickel(II) centers in [β- Ni 2 SiW 10 O 36 (OH) 2 (H 2 O) 2 ] 12− 

are in the 4,10 positions [173]. The structure of polyanion 11 can be viewed as a larger 

titanium-derivative of the trimeric, cyclic manganese(II)-substituted tungstosilicate [(β 2 - 

SiW 11 MnO 38 OH) 3 ] 15− . This product was also synthesized from [γ-SiW 10 O 36 ] 8− ) and it 

also contains beta-Keggin fragments [171]. However, the important difference to 11 is 

that its basic building block is a monosubstituted Keggin unit and as a result the Keggin- 

Keggin connectivities are accomplished via Mn-O-W bonds. It can be noticed that 11 

is not perfectly cyclic, but somewhat ellipsoidal (see Figures 3.41 (right)). This reflects 

the inequivalence of the two Ti-centers within each Keggin fragment. In 11, the short 

axis (distance between O3Ti and O3Ti’, see Figure 3.41(right)) is 10.8 Å, whereas the 

long axis is 13.0 Å (distance between O1TT and O1TT’). The reason for this is the fact 

that 1 contains two pairs of inequivalent Ti-O-Ti bridges: the type which involves two 

Ti centers in the rotated triad (Ti2-O1TT-Ti4, Ti2’-O1TT’- Ti4’, see Figure 3.41(right)) 

and the type which involves two Ti centers that are not in the rotated triad (Ti3-O3Ti- 

Ti3’,Ti1-O3Ti-Ti1). The two types of Ti-O-Ti bond angles are only marginally different: 

94

152.8(12) ◦ (Ti3-O3Ti-Ti3) vs. 153.9(12) ◦ (Ti2-O1TT-Ti4) in the solid state. All of the 

above indicates that 11 is best described as a dimer of dimers, which sheds some light 

Fig. 3.43: Dimer of Dimer of β(1,10)-Ti 2 (OH) 2 SiW 10 O 38 ] 6− 

on its mechanism of formation. Synthesis of 11 is accomplished by reaction of TiO(SO 4 ) 

with [γ-SiW 10 O 36 ] 8− , which means that the mechanism of formation of 11 must occur 

in the following sequence: (a) metal insertion, (b) rotational isomerization (γ-Keggin ·· 

β-Keggin), (c) dimer formation and (d) ring closure. Most likely insertion of two Ti 4+ 

ions into [γ-SiW 10 O 36 ] 8− leads to the monomeric species [γ-Ti 2 (OH) 2 SiW 10 O 38 ] 6− , which 

isomerizes to [β(1,10)-Ti 2 (OH) 2 SiW 10 O 38 ] 6− . This species is also unstable and dimerizes 

resulting in [β(1,10)- Ti 2 (OH)SiW 10 O 38 ] 2 (O) 12− , which is equivalent to the asymmetric 

unit of 11. In all structurally characterized Ti-substituted polyoxometalates the titanium 

atoms do not contain terminal bonds. Therefore it is not surprising that [β(1,10)- 

Ti 2 (OH)SiW 10 O 38 ] 2 (O) 12− is a highly reactive, dimeric species which reacts with other, 

identical dimers leading to the formation of 11. This “dimer of dimer mechanism” excludes 

the possibility of a gradual growth by individual Keggin units and it also implies 

that a trimeric intermediate is not present during formation of 11. Of course it is virtually 

impossible to proof the above hypothesis and the identity of the proposed intermediates 

experimentally, as formation of polyoxoanions occurs via rapid self-assembly as soon as 

the proper reaction conditions are present. We also investigated the solution properties of 

95

11 by 183 W-NMR (at 16.66 MHz on a JEOL Eclipse 400 instrument at room temperature 

using D 2 O as a solvent). We identified 10 major peaks of about equal intensity at 111.4, 

-118.0, - 122.8, -125.7, -141.4, -156.2, -157.8, -170.6, -173.8, - 221.0 ppm. This fits with the 

solid state structure of 11, because exactly this peak pattern is expected. Polyanion 11 has 

a center of inversion and the asymmetric unit (see Figure 3.41(right)) consists of 20 tungsten 

atoms. Each of the two Keggin fragments has a mirror plane so that 10 magnetically 

inequivalent tungsten pairs are present per asymmetric unit (W1/W2, W3/W8, W4/W7, 

W5/W6, W9/W10, W11/W12, W13/W18, W14/W17, W15/W16, W19/W20, see Figure 

3.41(right)). For the cyclic polyanion 11 this means that each of the 10 groups contains 

4 magnetically equivalent tungsten atoms. The 183 W-NMR spectrum also contains some 

additional peaks of much smaller intensity which we cannot assign yet. Nevertheless, any 

solid which precipitated or crystallized from the very concentrated 183 W-NMR solutions 

resulted in an FTIR spectrum identical to that of 11.In summary, we have synthesized 

a unique tetrameric and cyclic silicotungstate assembly using mild and one-pot reaction 

conditions. 


Polyanion 11 was fully characterized in solution and in the solid state by several analytical 

techniques. Formation of 11 indicates that (a) very large and cyclic Ti(IV)-substituted silicotungstates 

can be formed, (b) it might be possible to construct even larger wheel-shaped 

polyoxotungstates, (c) it might be possible to construct inorganic nanotubes by linking or 

orientating individual polyoxoanion wheels appropriately, (d) the gigantic, mixed-valence 

polyoxomolybdate wheels have some smaller, fully oxidized polyoxotungstate analogues, 

(e) the structural variety of supra- and supersupramolecular polyoxotungstates is just 

beginning to be explored and finally that (f) undoubtedly no other class of inorganic 

compounds besides polyoxometalates allows for preparation of discrete, nanomolecular 

objects of similar size,structure and function. 

96

Part-IV 

Cadmium and Indium Containing 

POMs

3.11 Structure and solution properties of the 

cadmium(II)-substituted tungstoarsenate: 

(Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ) 12− 


The transition metal substituted polyoxometalates (TMSPs), known to date are the class 

of sandwich-type species, probably the largest subfamily [175]. In 1973 Weakley et al. described 

the first sandwich-type polyoxoanion, [Co 4 (H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 10− [176]. Since 

then, several other derivatives of this structural type have been reported. To date, the 

class of Weakley-type sandwich species consists of the Keggin derivatives [M 4 (H 2 O) 2 (Bα-XW 

9 O 34 ) 2 ] n− (n = 12, X = Ge IV , Si IV , M = Mn 2+ , Cu 2+ , Zn 2+ , Cd 2+ ; n = 10, X = 

P V , As V , M = Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ ; n = 6, X = P V , As V , M = Fe 3+ ; 

n = 16, X = M = Cu 2+ ; n = 10, X = M = Fe 3+ ) and the Wells-Dawson derivatives 

[M 4 (X 2 W 15 O 56 ) 2 ] n− (X = P V , As V , n = 16, M = Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , 

n = 12, M = Fe 3+ ) [172, 176–195]. The second class of sandwich-type POMs is based on 

two lone-pair containing, α-Keggin fragments, e.g. [α-As III W 9 O 33 ] 9− . The first member 

of this class ([Cu 3 (H 2 O) 2 (α-AsW 9 O 33 ) 2 ] 12− ) was reported by Hervé et al. in 1982 [196]. 

Since then a number of isostructural derivatives has been characterized: [M 3 (H 2 O) 3 (α- 

XW 9 O 33 ) 2 ] n− (n = 12, X = As III , Sb III , M = Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ ; n = 10, X 

= Se IV , Te IV , M = Cu 2+ ) and [(VO) 3 (α-XW 9 O 33 ) 2 ] n− (n = 12, X = As III , Sb III , Bi III ; 

n = 11, X = As III ) [197–203]. Kortz et al. reported on the tri-palladium(II) substituted 

derivative [Pd 3 (α-SbW 9 O 33 ) 2 ] 12− .[204] The third class of sandwich-type POMs is based on 

two lone-pair containing, β-Keggin fragments, e.g. [β-Sb III W 9 O 33 ] 9− . The first members 

of this class, ([M 2 (H 2 O) 6 (WO 2 ) 2 (β-SbW 9 O 33 ) 2 ] (14−2n)− (M n+ = Fe 3+ , Co 2+ , Mn 2+ , Ni 2+ ), 

were reported by Krebs et al. in 1997 [69]. Since then some more isostructural derivatives 

have been characterized: ([M 2 (H 2 O) 6 (WO 2 ) 2 (β-BiW 9 O 33 ) 2 ] (14−2n)− (M n+ = Fe 3+ , Co 2+ , 

Ni 2+ , Cu 2+ , Zn 2+ ), [(VO(H 2 O) 2 ) 2 (WO 2 ) 2 (β-BiW 9 O 33 ) 2 ] 10− , [Sn 1.5 (WO 2 (OH)) 0.5 (WO 2 ) 2 

(β-XW 9 O 33 ) 2 ] 10.5− (X = Sb III , Bi III ), [M 3 (H 2 O) 8 (WO 2 )(β-TeW 9 O 33 ) 2 ] 8− (M = Ni 2+ , 

Co 2+ ), [(Zn(H 2 O) 3 ) 2 (WO 2 ) 1.5 (Zn(H 2 O) 2 ) 0.5 (β-TeW 9 O 33 ) 2 ] 8− , [(VO(H 2 O) 2 ) 1.5 (WO(H 2 O) 2 ) 0.5 

98

(WO 2 ) 0.5 (VO(H 2 O)) 1.5 (β-TeW 9 O 33 ) 2 ] 7− and [M 4 (H 2 O) 10 (β-XW 9 O 33 ) 2 ] n− (n = 6, X = 

As III and Sb III , M = Fe III and Cr III ; n = 4, X = Se IV , Te IV , M = Fe III and Cr III ; n 

= 8, X = Se IV , Te IV , M = Mn II , Co II , Ni II , Zn II , Cd II and Hg II ) [83, 203, 205–207]. 

The fourth class of sandwich-type POMs is based on two A-α-Keggin fragments, e.g. 

[A-α-PW 9 O 34 ] 9− . The first member of this class, [Co 3 ](H 2 O) 3 (A-α-PW 9 O 34 ) 2 ] 12− , was 

reported by Knoth et al. in 1985 [208]. Since then the following isostructural derivatives 

have been identified: [M 3 (A-XW 9 O 34 ) 2 ] n− (n = 14, X = Si IV , M = Sn 2+ , Co 2+ ; n = 

12, X = P V , M = Mn 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Pd 2+ , Sn 2+ ; n = 9, X = P V , M = Fe 3+ ), 

[(CeO) 3 (H 2 O) 2 (A-PW 9 O 34 ) 2 ] 12− and [(ZrOH) 3 (A-SiW 9 O 34 ) 2 ] 11− [209–212]. Very recently 

Kortz et al. reported on the di-palladium(II) substituted derivative [Pd 2 WO(H 2 O)(A-α- 

SiW 9 O 34 ) 2 ] 12− .[167] Surprisingly little work on cadmium-substituted polyoxotungstates 

has been reported to date, especially regarding structurally characterized species. Nevertheless, 

the diamagnetic nature of Cd-containing POMs has prompted some NMR studies. 

Twenty years ago Contant reported for the first time on cadmium-containing Keggin and 

Wells-Dawson species [213–215]. In 1995 Kirby and Baker reported on a NMR study 

of the first sandwich-type polyoxometalate including Cd 2+ ions [216]. More recently, Bi 

et al. synthesized Cd-substituted, sandwich type polyanions based on the tungstoarsenate 

fragments [As 2 W 15 O 56 ] 12− and [AsW 9 O 34 ] 9− , respectively.[191, 192] Very recently, 

Alizadeh et al. synthesized and structurally characterized the tetra-cadmium containing 

[Cd 4 (H 2 O) 2 (PW 9 O 34 ) 2 ] 10− [217]. Here we report on interaction of Cd 2+ ions with the 

trilacunary Keggin derivative [A-HAsW 9 O 34 ] 8− in aqueous solution. 


Synthesis of lacunary polyanion precursor Na 8 [A-HAsW 9 O 34 ]·11H 2 O : A 30 g (91 mmol) 

sample of Na 2 WO 4·2H 2 O and 1.18 g (5.1 mmol) As 2 O 5 were dissolved in 40 mL of water. 

Subsequently, the pH was adjusted to 8.4 using glacial acetic acid. After a few 

seconds the solution became cloudy and after about 2 min. a white precipitate started 

to form. The solution was stirred for another 30 min. and then the solid was isolated 

on a sintered funnel. The product was washed three times with ethanol and air-dried 

with aspiration. FTIR spectroscopy: 937(m), 884(m), 851(m), 765(s), 672(m), 518(w), 

99

472(w), 444(w) cm −1 . This procedure is different from that reported previously by one of 

us, which involves using H 3 AsO 4 instead of As 2 O 5 .[72] Synthesis of Cs 4 K 3 Na 5 [Cd 4 Cl 2 (Bα-AsW 

9 O 34 ) 2 ]·20H 2 O (CsKNa-12) A 0.33 g (1.66 mmol) sample of CdCl 2·H 2 O was 

dissolved with stirring in 20 mL of 0.5 M NaAc buffer (pH 4.8). Then 2.00 g (0.75 mmol) 

of Na 8 [A-HAsW 9 O 34 ]·11H 2 O was added. The solution was heated to ∼80 ◦ C for about 1 

h and filtered after it had cooled. Then 0.5 mL of 1.0 M CsCl and 0.5 mL of 1.0 M KCl 

solutions were added to the filtrate. Slow evaporation at room temperature led to 1.8 

g (yield 78%) of a white crystalline product after about one week. FTIR spectroscopy: 

951(s), 882(s), 835(s), 784(s), 746 (sh), 724 (s), 480 (w), 442 (w) cm −1 . Anal. Calcd 

(Found) for 1a: Cs 8.6 (8.3), K 1.9 (2.1), Na 1.9 (1.9), W 53.4 (53.9), Cd 7.3 (7.1), As 

2.4 (2.4), Cl 1.2(1.3). Polyanion 13 was prepared by an analogous procedure as 12, but 

Fig. 3.44: FTIR spectra of compound (CsKNa-12)(red) and Na 8 [A-HAsW 9 O 34 ]·11H 2 O (blue) 

Cd(NO 3 ) 2·4H 2 O was used instead of CdCl 2·H 2 O to ascertain the absence of chloride ions. 


A colorless crystal with dimensions 0.26 × 0.12 × 0.08 mm was selected and mounted on 

a glass fiber for indexing and intensity data collection at 167 K on a Bruker D8 SMART 

APEX CCD single-crystal diffractometer using Mo Kα radiation (λ = 0.71073 Å). Direct 

methods were used to solve the structure and to locate the heavy atoms (SHELXS97). 

Then the remaining atoms were found from successive difference maps (SHELXL97). 

100

Fig. 3.45: FTIR spectra of compound (CsNa-13)(red) and Na 8 [A-HAsW 9 O 34 ]·11H 2 O (blue) 

Routine Lorentz and polarization corrections were applied and an absorption correction 

was performed using the SADABS program [81]. Crystallographic data are summarized 

in Table 3.11. 

Table 3.11: Crystal Data and Structure Refinement for compound CsKNa-12 

Emperical formula Cs 4 K 3 Na 5 [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ]·20H 2 O 

fw 6192.0 

space group (No.) P 2 1 /n (14) 

a (Å) 13.1402(12) 

b (Å) 19.0642(17) 

c (Å) 17.5666(15) 

vol (Å 3 ) 4400.5(7) 

Z 2 

temp ( ◦ C) -106 


d calcd (mg m −3 ) 4.608 

abs coeff. (mm −1 ) 27.069 

R [I > 2 σ(I)] a 0.046 



Solution NMR spectroscopy: 183 W and 111 Cd NMR 

All NMR spectra were recorded on a 400 MHz JEOL ECX instrument at room temperature 

using D 2 O as a solvent. The 183 W-NMR measurements were performed at 16.656 

101

MHz in 10 mm tubes and the 111 Cd NMR measurements were performed at 84.757 MHz 

in 5 mm tubes. As references (external standards) we used aqueous solutions of 1 M 

Na 2 WO 4 and 0.1 M Cd(ClO 4 ) 2 , respectively. 183 W NMR is a very powerful solution technique 

in polyanion chemistry to obtain structural information. The fact that polyanions 

12 and 13 are diamagnetic makes them ideal candidates for NMR studies. In addition 

both species contain cadmium ions and therefore we decided to perform a detailed 183 W 

and 111 Cd NMR study on 12 and 13. If the dimeric, sandwich-type polyanion structure 

with C 2h symmetry is preserved in solution, then five peaks (intensity ratio 2:2:2:2:1) are 

expected in 183 NMR and two peaks (1:1) are expected for 111 Cd NMR. In fact, this is 

exactly what we observed. The room-temperature 183 W-NMR spectrum of 12 exhibits 

five peaks at -75.9, -92.0, -94.2, -109.8, -121.8 ppm with intensity ratios 1:2:2:2:2 (see 

Figure 3.46, top). For 13 we obtained an almost identical spectrum with five peaks at 

-75.9, -92.6, -94.3, -107.9, -119.9 ppm and the anticipated intensity ratios (see Figure 3.46, 

bottom). As expected, a change of the terminal ligand on the external cadmium centers 

in 12 and 13 does not affect the chemical shifts of the tungsten centers significantly. In 

fact, only four of the six belt tungsten atoms in each Keggin unit should be affected, 

as they are only 3 bonds from the terminal chloro ligands in 12 or aqua ligands in 13 

(see Figure 3.45). Therefore we suggest that the two upfield signals in the 183 W NMR 

spectra of 12 and 13 (see Figure 3.46) correspond most likely to those tungsten atoms in 

question. All other tungsten centers are further away from the terminal cadmium ligands 

in 12 and 13. Of course, the unique cap tungsten atom corresponds to the smallest, most 

downfield signal. The 183 W NMR spectra of 12 and 13 correspond also very nicely to our 

results on the isostructural germanium derivatives [Cd 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− and 

[Zn 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− .[195] The 111 Cd NMR spectrum of 12 shows two singlet 

peaks at 55.3 and 14.7 ppm, respectively (see Figure 3.47, top). The upfield signal is very 

broad which is probably due to the quadrupolar moment of the chloro ligand. Therefore, 

we can assign this signal to the external cadmium ions in 12 whereas the other, sharp 

signal corresponds to the internal cadmium centers. The 111 Cd NMR spectrum of 13 

exhibits two sharp peaks at 57.0 and 11.1 ppm, respectively with equal intensities (see 

Figure 3.47, bottom). This is fully consistent with water molecules as terminal ligands 

102

Fig. 3.46: 183 W NMR spectra of [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− (12), top, and [Cd 4 (H 2 O) 2 (B-α- 

AsW 9 O 34 ) 2 ] 10− (13) 

on the external cadmium ions. In analogy to 12 we assign the upfield signal at 11.1 

ppm to the external cadmium ions and the downfield signal at 57.0 ppm to the internal 

cadmium ions of 13. These results are also in good agreement with Alizadeh et al., who 

performed 113 Cd NMR studies on [Cd 4 (H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 10− . They observed a very 

similar chemical shift for the internal cadmium ions (52.76 ppm), but the signal for the 

outer cadmium centers is significantly more downfield (26.25 ppm) [217]. This difference 

in 111 Cd NMR behavior must be due to the different hetero atoms X (X = As v , P v ), 

as all other parameters are the same for both polyanions (e.g. structure, charge). Our 

work shows that this ‘hetero atom effect’ is more pronounced for the external than the 

internal cadmium ions. The nuclear shielding of the outer cadmium centers is a much 

better sensor for the type of hetero atom present than that of the internal cadmiums, in 

spite of the fact that the Cd-O bond lengths and Cd-O-X angles are very similar in both 

103

Fig. 3.47: 111 Cd NMR spectra of [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− 12, top, and [Cd 4 (H 2 O) 2 (B-α- 

AsW 9 O 34 ) 2 ] 10− 13, bottom. 

cases. 


We have synthesized the dimeric tungstoarsenate(V) [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− (1) as 

a mixed cesium-potassium-sodium salt. The title polyanion consists of two trilacunary 

[B-α-AsW 9 O 34 ] 9− Keggin units linked via a rhomblike Cd 4 O 14 Cl 2 group resulting in a 

sandwich-type structure with idealized C 2h symmetry (see Figure 3.48). Polyanion 12 was 

synthesized by interaction of Cd 2+ ions with the trilacunary precursor [A-HAsW 9 O 34 ] 8− 

in aqueous acidic medium upon heating to ∼80 ◦ C. This indicates that the Keggin precursor 

has undergone isomerization from A-AsW9 → B-AsW9 during the course of the 

reaction. However, this transformation is well known and has been observed in solution 

and in the solid state [192]. Bond valence sum (BVS) calculations confirm that there are 

no protonation sites on 12, indicating that the charge of the title polyanion must be 12 

[85]. Crystallographically we could identify only 4 Cs + , 3 K + and 3 Na + counterions, 

104

Fig. 3.48: Combined polyhedral and ball and stick representation of [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− 

but elemental analysis indicated that indeed 5 Na + ions were present in 12. Therefore 

the charge of 12 for 12 is fully balanced in the solid state by an appropriate number of 

counter ions. Disorder of some alkali ions (in particular sodium) is a common problem 

in polyanion chemistry. The structural type of 12 had first been described in 1973 by 

Weakley et al. for [Co 4 (H 2 O) 2 (PW 9 O 34 ) 2 ] 10− [10a]. To date this Keggin-based structure 

is known for most first-row transition metals (including mixed-metal derivatives) 

and it has also been possible to substitute the tetrahedral phosphorus(V) heteroatom by 

arsenic(V), silicon(IV), germanium(IV), iron(III), and copper(II) [172, 176–195]. Therefore, 

this structural type represents one of the largest TMSP families. The Weakley-type 

structures have in common that the two external transition metal ions in the central rhombus 

have one terminal ligand each, whereas the two internal metal ions do not have any 

terminal ligands. In all of the above known derivatives with the Weakley structure, the 

terminal ligand on the external transition metal ions is a water molecule. However, in 12 

the two external cadmium ions have a chloro ligand instead of a water molecule. Clearly, 

the chloride ions originate from the cadmium source (CdCl 2·H 2 O) which we used for the 

synthesis of 12. Nevertheless, it must be remembered that synthesis of 12 is carried out 

105

in aqueous solution, so that the number of water molecules dominates by far the chloride 

ions. Therefore, the external cadmium ions incorporated in 12 have a strong preference 

for chloro rather than aqua ligands. Recently one of us reported on the aqua derivative 

of 12 which was formulated as [Cd 4 (H 2 O) 2 (B-α-AsW 9 O 34 ) 2 ] 10− based on FTIR spectroscopy 

[72]. Very recently Alizadeh et al. reported on [Cd 4 (H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 10− 

which represents the phosphorus derivative of 12 [217]. They prepared this polyanion by 

reaction of Cd(NO 3 ) 2·4H 2 O with Na 8 [A-α-HPW 9 O 34 ]·24H 2 O in aqueous acidic medium 

(pH 6). These authors characterized their product in solution by 31 P and 113 Cd NMR 

spectroscopy. Very recently our group has synthesized the germanium(IV) derivative 

[Cd 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− by reaction of CdCl 2 , GeO 2 , and Na 2 WO 4·2H 2 O in 0.5 

M sodium acetate buffer (pH 4.8) [195]. Interestingly, the external cadmium ions in the 

product polyanion contain aqua rather than chloro ligands. It is possible that the higher 

affinity of Cd 2+ for chloro ions is overcompensated by charge density considerations of 

the germanium(IV) based polyanion. Specifically, the hypothetical dichloro derivative 

[Cd 4 Cl 2 (B-α-GeW 9 O 34 ) 2 ] 14− would have a charge of 14-, which is apparently less stable 

than the diaqua derivative [Cd 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− with a charge of 12-. Interestingly, 

our [Cd 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− and the [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− reported 

here have both the same charge of 12-. It is of interest to evaluate in detail the bond 

lengths and angles of the cadmium centers in 12 and to compare these with the isostructural 

derivatives [Cd 4 (H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 10− and [Cd 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− . In 

general, as Cd 2+ is a d 10 ion no Jahn-Teller distortion is expected. In fact, the two inner 

Cd centers of 12 exhibit a fairly regular coordination sphere and the Cd(1)-O distances 

range from 2.19-2.34(1) Å. On the other hand, the coordination sphere of the external 

Cd(2) shows a Jahn-Teller distortion, which is most likely due to the presence of 

the terminal chloro ligand. The equatorial Cd(2)-O distances range from 2.24-2.29(1) Å, 

whereas the axial Cd(2)-O and Cd(2)-Cl distances are 2.47(1) and 2.475(4) Å, respectively. 

The bond angles in the central Cd 4 Cl 2 O 14 fragment can be classified according 

to the type of bridging ligand. The Cd-O-Cd angles involving the µ 4 -oxo ligand O1As 

are: Cd1-O1As-Cd1’ 101.2(4) ◦ , Cd1-O1As-Cd2 93.3(3) ◦ and Cd1-O1As-Cd2 94.6(3) ◦ , 

respectively. On the other hand, the angles around the µ 3 -oxo ligands O8C2 and O9Cd 

106

are: Cd1-O8C2-Cd2 98.9(4) ◦ and Cd1-O9Cd-Cd2 100.4(4) ◦ . The Cd···Cd separations 

in 1 are as follows: Cd1···Cd2 3.533(2) Å, Cd1···Cd2’ 3.494(2) Å and Cd1···Cd1’ 3.614(2) 

Å, respectively. Comparison of these parameters for 12 with those of the structurally 

closely related [Cd 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− [195] and [Cd 4 (H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 10− 

[217] allows to draw the following conclusions: the terminal chloro ligands in 12 result in 

a significantly longer terminal cadmium bond (Cd-Cl 2.475 (5) Å) compared to those in 

the two aqua compounds (2.260 (14) and 2.309(8) Å). This is the reason for the more 

pronounced Jahn-Teller distortion of the external Cd centers in 12, which in turn results 

in larger Cd1···Cd2 distances (e.g. 3.494(2) Å, 3.533(2) Å in 1 vs. 3.357(2) Å, 3.404(2) Å 

in [Cd 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− ). We were also able to synthesize the aqua derivative 

of 12 with the proposed formula [Cd 4 (H 2 O) 2 (B-α-AsW 9 O 34 ) 2 ] 10− 13 as based on FTIR 

and multinuclear NMR spectroscopies. 


The dimeric, cadmium-substituted tungstoarsenate [Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− Polyanion 

13 was prepared by an analogous procedure as 12, but Cd(NO 3 ) 2·4H 2 O was used 

instead of CdCl 2·H 2 O to ascertain the absence of chloride ions. Polyanion 13 has been 

synthesized by reaction of Cd 2+ ions with [A-HAsW 9 O 34 ] 8− in aqueous, acidic medium. 

has a sandwich-type structure based on two [B-α-AsW 9 O 34 ] 9− Keggin moieties encapsulating 

four cadmium centers in a rhomblike (Cd 4 O 14 Cl 2 ) group. Therefore, 12 represents 

only the second structurally characterized, Cd-containing polyanion and it is the first 

structurally characterized, Cd-containing tungstoarsenate(V). An interesting aspect of 

12 is the fact that the external cadmium centers have terminal chloro ligands. Nevertheless, 

we were also able to synthesize the aqua derivative [Cd 4 (H 2 O) 2 (B-α-AsW 9 O 34 ) 2 ] 10− 

13. Both species were investigated by 183 W and 111 Cd NMR in solution and we have 

shown that the former is an ideal method to establish the purity and to confirm the overall 

polyanion structure of 12 and 13. On the other hand, the latter is an ideal technique 

to study the local coordination environment of the cadmium ions and it also allows to 

clearly distinguish 12 and 13 due to peak broadening caused by the quadrupolar chloride 

ions. Furthermore, this effect allows to assign the two Cd-NMR peaks to the two types 

107

of cadmium ions in 12 and 13 and it also allows to indirectly assign some of the 183 W 

NMR peaks of the title polyanions. In conclusion, synthesis of diamagnetic derivatives 

(e.g. Cd 2+ , Zn 2+ ) of TMSPs is very attractive, as it allows to perform multinuclear NMR 

studies in solution involving addenda atoms (e.g. 183 W 111 Cd). Although single crystal 

X-ray analysis is the most powerful technique to establish novel polyanion structures, 

multinuclear NMR is a very important, complementary tool to establish the structural 

integrity of polyanions in solution. Considering that polyanions have a multitude of potential 

applications in solution (e.g. medicine, catalysis) such diamagnetic complexes can 

be considered as model compounds to help understand structure-activity relationships of 

entire families of polyanions. 

3.12 Some indium(III)-substituted polyoxotungstates 

of the Keggin and Dawson type 


The synthesis of polyoxometalates (POMs) is mostly straightforward, once the proper reactions 

conditions have been identified. However, the mechanism of formation of POMs is 

not yet well understood and commonly described as self-assembly. Therefore, the design 

of novel POMs remains a challenge for synthetic chemists. The most rational synthesis 

procedure of POMs involves the use of lacunary precursors. Lacunary POMs are 

usually synthesized from complete precursor ions by loss of one or more MO 6 octahedra. 

Reaction of a stable, lacunary polyoxometalate with transition metal ions usually 

leads to a product with the heteropolyanion framework unchanged. This approach usually 

results in monomeric or dimeric polyoxoanions with expected structures, e.g. [A-α- 

SiW 9 O 34 ] 10− + 3Cu 2+ −→ [Cu 3 (H 2 O) 3 (A-α-SiW 9 O 37 ] 10− and 2[B-α -PW 9 O 34 ] 9− + 4Co 2+ 

−→[Co 4 (H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 10− .[176, 218] 

Sandwich-type POMs based on two [B-α-XW 9 O 34 ] n− (X = P V , As V , Si IV , Ge IV ) or 

[X 2 W 15 O 56 ] 12− (X = P V , As V ) fragments and four transition metal centers constitute a 

well-known class of compounds [195]. To date a large number of derivatives has been 

reported for both the Keggin and Wells-Dawson type structures. It has become apparent 

108

that this dimeric, sandwich-type structure (Weakley-type) allows for incorporation of essentially 

all first-row and some second row transition metal ions [195]. 

Recently several examples of Weakley-type sandwich POMs with less than four transition 

metals have been reported [219]. Hill et al. described di- and tri-iron-substituted 

polyanions of the Wells-Dawson-type and interestingly the vacancies were occupied by 

sodium ions (e.g. [Fe 2 (NaOH 2 ) 2 (P 2 W 15 O 56 ) 2 ] 16− , [Fe 2 (FeOH 2 )(NaOH 2 )(P 2 W 15 O 56 ) 2 ] 14− ). 

However, it has been possible to substitute these sodium ions by first row-transition 

metal ions leading to mixed-metal sandwich-type polyanions [219]. The first example of 

a tri-substituted, sandwich-type polyoxoanion based on a Keggin fragment is also known 

([Ni 3 Na(H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 11− [220]. 

Lone pair containing polyoxotungstates (e.g. [Cs 2 Na(H 2 O) 10 Pd 3 (α-Sb III W 9 O 33 ) 2 ] 9− , 

[Cu 4 K 2 (H 2 O) 8 ](α-As III W 9 O 33 ) 2 ) 8− ), [As III 6W 65 O 217 (H 2 O) 7 ] 26− ) are a well-established subclass 

of POMs [33, 202, 204]. The presence of a lone pair on the hetero element does not 

allow the closed Keggin unit to form. The dimeric, sandwich-type POMs based on two 

lone pair containing, β-Keggin fragments (e.g. [β -As III W 9 O 33 ] 9− , [β-Sb III W 9 O 33 ] 9− ) 

represent also a well-known class of sandwich-type POMs. The first members of this 

class, ([M 2 (H 2 O) 6 (WO 2 ) 2 (β-SbW 9 O 33 ) 2 ] (14−2n)− (M n+ = Fe 3+ , Co 2+ , Mn 2+ , Ni 2+ ), were 

reported by Krebs et al. in 1997 [69]. Since then some more isostructural derivatives 

have been characterized: ([M 2 (H 2 O) 6 (WO 2 ) 2 (β-BiW 9 O 33 ) 2 ] (14−2n)− (M n+ = Fe 3+ , Co 2+ , 

Ni 2+ , Cu 2+ , Zn 2+ ), [(VO(H 2 O) 2 ) 2 (WO 2 ) 2 (β-BiW 9 O 33 ) 2 ] 10− , [Sn 1.5 (WO 2 (OH)) 0.5 (WO 2 ) 2 ( 

β-XW 9 O 33 ) 2 ] 10.5− (X=Sb III ,Bi III ), [M 3 (H 2 O) 8 (WO 2 )(β-TeW 9 O 33 ) 2 ] 8− (M=Ni 2+ ,Co 2+ ), 

[(Zn(H 2 O) 3 ) 2 (WO 2 ) 1.5 (Zn(H 2 O) 2 ) 0.5 (β-TeW 9 O 33 ) 2 ] 8− , [(VO(H 2 O) 2 ) 1.5 (WO(H 2 O) 2 ) 0.5 (WO 2 ) 

0.5(VO(H 2 O)) 1.5 (β-TeW 9 O 33 ) 2 ] 7− and [M 4 (H 2 O) 10 (β-XW 9 O 33 ) 2 ] n− (n = 6, X = As III and 

Sb III , M = Fe III and Cr III ; n = 4, X = Se IV , Te IV , M = Fe III and Cr III ; n = 8, X = 

Se IV , Te IV , M = Mn II , Co II , Ni II , Zn II , Cd II and Hg II [83, 203, 205–207]. 

It becomes apparent that most of the known sandwich-type POMs contain divalent, paramagnetic 

transition metal ions. The motivation for synthesizing such compounds in the 

first place is usually centered around perceived applications in catalysis and medicine. 

Therefore, it is highly important to also investigate the solution properties of such POMs 

in addition to the solid state. The most sensitive and elegant tool for such studies is un- 

109

doubtedly 183 W-NMR, but the paramagnetic nature of most sandwich-type POMs complicates 

matters. Therefore, it is of interest to prepare isostructural and diamagnetic 

analogs of these compounds. 

In several cases it was possible to substitute the divalent, paramagnetic transition metal 

ions by diamagnetic Zn 2+ and then 183 W-NMR was used to proof the structural integrity 

of the POMs in solution (e.g. [M 3 (H 2 O) 3 (α-XW 9 O 33 ) 2 ] 12− (M = Cu 2+ , Zn 2+ ; X = As III , 

Sb III ) [39, 195]. Obviously, substitution of Fe(III)-containing POMs by Zn 2+ results in 

derivatives with a different charge (e.g. [Fe 4 (H 2 O) 10 (β-SeW 9 O 33 ) 2 ] 4− vs [Zn 4 (H 2 O) 10 (β- 

SeW 9 O 33 ) 2 ] 8− ). In order to solve this problem, we decided to prepare In(III)-substituted 

POMs with structures for which Fe(III)-analogs exist. 

Interestingly, very little work on indium-substituted polyoxometalates has been reported 

to date [221–223]. In 1995, Liu et al. described interaction of indium(III) with the trilacunary 

Keggin species α,β-[XW 9 O 34 ] 10− (X = Si, Ge) and based on 183 W-NMR they proposed 

trisubstituted, monomeric products [221]. A few years later, Wasfi et al. synthesized 

an indium(III) substituted heteropolyfluorotungstate and they proposed a Dawson-like 

structure [222]. Very recently, Krebs et al. described the first structurally characterized, 

indium(III) substituted polyanions [223]. Here we report on tri- and tetra-indium(III) 

substituted polyoxotungstates based on Keggin and Wells-Dawson fragments. 


The lacunary precursors Na 8 H[B-α-PW 9 O 34 ], Na 12 [P 2 W 15 O 56 ], Na 9 [α-AsW 9 O 33 ] and Na 9 [α- 

SbW 9 O 33 ] were synthesized according to published procedures and their purity was confirmed 

by infrared spectroscopy [69, 73, 75, 128]. All other reagents were used as purchased 

without further purification. 

D,L-(NH 4 ) 11 [In 3 Cl 2 (B-α-PW 9 O 34 ) 2 ]· 16H 2 O (NH4-14). A 0.39 g (1.76 mmols) sample of 

InCl 3 was dissolved in 40 mL H 2 O followed by addition of 1.94 g (0.80 mmol) Na 8 H[B-α- 

PW 9 O 34 ]. The pH of this solution was adjusted to 2 by addition of 4 M HCl and then 

it was heated to ∼80 ◦ C for 1 h. After cooling to room temperature the solution was 

filtered. Then it was layered with 0.1 M NH 4 Cl and allowed to evaporate in an open 

beaker at room temperature. After 1-2 days a white crystalline product started to ap- 

110

pear. Evaporation was allowed to continue until the solvent level had approached the 

solid product, which was filtered off and air-dried (1.6 g, yield 75 %). FTIR spectroscopy: 

1079(m), 1069(m), 1054(sh), 995(sh), 983(s), 963(sh), 885(m), 797(s), 728(sh), 681(sh), 

595(w), 522(w) cm −1 . Elemental analysis calcd. (found): N 2.9 (2.7), In 6.4 (6.5), P 1.2 

(1.1), W 61.7 (62.2), Cl 1.3 (1.0) %. 

31 P-NMR (D 2 O, 293 K): -11.4 ppm; 183 W-NMR (D 2 O, 293 K): (relative intensities 

in parenthesis) -98.3(1), -104.2(2), -128.6(2), -129.1(1), -133.1(2), -186.6(1)ppm. D,L- 

(NH 4 ) 9 Na 8 [In 3 Cl 2 (P 2 W 15 O 56 ) 2 ]·39H 2 O (NH4Na-15). A 0.39 g (1.76 mmols) sample of 

InCl 3 was dissolved in 40 mL H 2 O followed by addition of 3.52 g (0.80 mmol) 

Na 12 [P 2 W 15 O 56 ]·24H 2 O. The pH of this solution was adjusted to 2 by addition of 4 M 

HCl and then it was heated to ∼80 ◦ C for 1 h. After cooling to room temperature the 

solution was filtered. Then it was layered with 0.1 M NH 4 Cl and allowed to evaporate in 

an open beaker at room temperature. After 1-2 days a white crystalline product started 

appear. Evaporation was allowed to continue until the solvent level had approached the 

solid product, which was filtered off and air-dried (2.5 g, yield 69 %). FTIR spectroscopy: 

1092(s), 1059(m), 1017(w), 944(s), 917(s), 882(m), 831(sh), 810(sh), 764(s), 721(sh), 

641(sh), 598(sh), 524(w) cm −1 . Elemental analysis calcd. (found): Na 2.1 (2.1), N 1.4 

(1.2), In 3.9 (4.0), P 1.4 (1.3), W 62.0 (61.3), Cl 0.8 (0.9) %. 31 P-NMR (D 2 O, 293 K): 

(relative intensities in parenthesis) -7.1(1), -13.3(1) ppm. 

RbNa 3 [In 4 (H 2 O) 10 (β -AsW 9 O 32 OH) 2 ]·36H 2 O (RbNa-16). A 0.39 g (1.76 mmols) sample 

of InCl 3 was dissolved in 40 mL H 2 O followed by addition of 2.00 g (0.80 mmol) Na 9 [α- 

AsW 9 O 33 ]. The pH of this solution was adjusted to 2 by addition of 4 M HCl and 

then it was heated to ∼80 ◦ C for 1 h. After cooling to room temperature the solution 

was filtered. Then it was layered with 0.1 M RbNO 3 and allowed to evaporate in an 

open beaker at room temperature. After 1-2 days a white crystalline product started 

to appear. Evaporation was allowed to continue until the solvent level had approached 

the solid product, which was filtered off and air-dried. A total of 1.7 g (yield 72%) of 

crystalline product was obtained. FTIR spectroscopy: 955(m), 881(sh), 823(s), 794(s), 

701(m), 614(sh), 510(sh), 478(w), 430(w) cm −1 . Elemental analysis calcd. (found): Rb 

1.4 (1.2), Na 1.2 (1.1), In 7.7 (7.5), As 2.5 (2.5), W 55.5 (55.0) %. 183 W-NMR (D 2 O, 293 

111

K): (relative intensities in parenthesis) -102.3(1), -109.6(2), -153.7(2), -171.3(2), -199.2(2) 

ppm. 

K 4 Na 2 [In 4 (H 2 O) 10 (β -SbW 9 O 33 ) 2 ]·30H 2 O (KNa-17). The synthesis was identical to that 

of (KNa-17), with the exception that 2.00 g (0.80 mmol) Na 9 [α-SbW 9 O 33 ] was used 

instead of Na 9 [α-AsW 9 O 33 ]. In addition, the solution was layered with 0.1 M KCl instead 

of RbNO 3 . In this case a total of 2.0 g (yield 82%) of crystalline product was obtained. 

FTIR spectroscopy: 949(m), 890(sh), 809(s), 693(m), 604(sh), 507(w), 467(w), 418(w) 

cm −1 . Elemental analysis calcd. (found): K 2.6 (2.8), Na 0.8 (0.5), In 7.7 (7.6), Sb 

4.1 (4.0), W 55.2 (55.9) %. We have also isolated the selenium(IV) and tellurium(IV) 

containing derivatives K 4 [In 4 (H 2 O) 10 (β-SeW 9 O 33 ) 2 ]·28H 2 O (K-18) and K 4 [In 4 (H 2 O) 10 (β 

-TeW 9 O 33 ) 2 ]·29H 2 O (K-19), respectively, as based on FTIR spectroscopy and elemental 

analysis. FTIR spectra for K-18: 954(m), 890(sh), 819(s), 765(s), 653(m), 504(w), 447(w) 

cm −1 . FTIR for K-19: 971(m), 889(m), 784(s), 749(m), 612(sh), 509(w), 423(w) cm −1 . 

Elemental analysis for (K-18) calcd.(found): K 2.7 (2.5), In 7.9 (7.6), Se 2.7 (2.8), W 56.8 

(57.5) %. Elemental analysis for K-19 calcd. (found): K 2.6 (2.7),In 7.7 (7.5), Te 4.3 (4.1), 

W 55.7 (56.2) %. Elemental analyses were performed by Kanti Labs Ltd. in Mississauga, 

Canada. FTIR spectra were recorded on a Nicolet Avatar FTIR spectrophotometer in a 

KBr pellet. All NMR spectra were recorded at room temperature with freshly synthesized 

solutions of 14-17 on a 400 MHz JEOL ECX instrument. 


Single crystals of compounds NH4-14 and KNa-17 were mounted on a glass fiber for 

indexing and intensity data collection at 173 K for compound NH4-14 and KNa-17 and 

200 K for compound NH4Na-15 and RbNa-16, respectively, on a Bruker D8 SMART 

APEX CCD single-crystal diffractometer using Mo K α radiation ( λ = 0.71073 Å). Direct 

methods were used to solve the structures and to locate the heavy atoms (SHELXS97). 

Then the remaining atoms were found from successive difference maps (SHELXL97). 

Routine Lorentz and polarization corrections were applied and an absorption correction 

was performed using the SADABS program [81]. Crystallographic data are summarized 

in Table 3.12. 

112

Table 3.12: Crystal Data and Structure Refinement for compounds NH4-14, NH4Na-15, RbNa-16 

and KNa-17 

Compounds NH4-14 NH4Na-15 RbNa-16 KNa-17 

fw 5361.5 8895.91 5959.8 5991.3 

space group P 2 1 /n (14) P ¯1 (2) P ¯1 (2) P ¯1 (2) 

a (Å) 17.5090(10) 13.0643(5) 12.8142(5) 12.2306(9) 

b (Å) 12.7361(7) 14.8901(6) 12.8672(5) 12.7622(10) 

c (Å) 18.7955(11) 19.8603(8) 16.1794(7) 16.1639(12) 

α ( ◦ ) 92.2920(10) 91.1370(10) 73.9890(10) 

β( ◦ ) 107.3030(10) 90.8680(10) 105.9450(10) 76.5550(10) 

γ ( ◦ ) 100.5630(10) 104.0980(10) 86.2130(10) 

vol. (Å 3 ) 4001.6(4) 3793.9(3) 2477.02(17) 2358.7(3) 

Z 2 1 1 1 

temp. ( ◦ C) -100 -73.3 -73.3 -100 

wavelength (Å) 0.71073 0.71073 0.71073 0.71073 

dcalc (Mg m −3 ) 4.404 3.851 3.918 4.167 

abs. coeff. (mm −1 ) 26.837 23.301 22.995 23.674 

R [I > 2 σ(I)] a 0.04 0.054 0.047 0.061 

R w (all data) b 0.075 0.133 0.119 0.113 



The dimeric, chiral polyoxoanion [In 3 Cl 2 (B-α-PW 9 O 34 ) 2 ] 11− 14 is composed of two (Bα-PW 

9 O 34 ) units linked via three In(III) ions (see Figure 3.49). Polyanion 14 belongs 

to the well-known class of sandwich-type structures (Weakley type) and it represents the 

first indium-derivative [195]. Interestingly, only three indium centers are incorporated in 

14 and it is very unusual that one of the inner positions is vacant. Both outer positions 

are occupied by indium ions with a terminal chloro ligand each. Therefore polyanion 14 

exhibits C 2 point group symmetry (as opposed to C 2h for the tetrasubstituted transition 

metal analogs, e.g. [Mn 4 (H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 10− ) indicating that it is chiral. The only 

other trisubstituted analog of 14 known to date is [Ni 3 Na(H 2 O) 2 (B-α-PW 9 O 34 ) 2 ] 11− , but 

in this case the ‘vacant’ site is in an outer position and it is occupied by a sodium ion 

in the solid state [220]. Bond lengths and angles associated with the central indium-oxo 

fragment of 14 are shown in Table 3.13. 

The structure of 14 and its chiral nature somewhat resemble Tourné’s polyanion 

[WM 3 (H 2 O) 2 (B-α-XW 9 O 34 ) 2 ] 12− (X = M = Zn 2+ , Co 2+ ) [224]. Due to the fact that most 

polyoxoanions are not inherently chiral, Tourné’s species and especially its noble metal 

113

Fig. 3.49: Combined polyhedral/ball and stick representation of [In 3 Cl 2 (PW 9 O 34 ) 2 ] 11− 14The red octahedra 

represent WO 6 , the blue tetrahedra represent PO 4 and the balls represent indium (green) and 

chlorine (yellow). 

containing derivatives (e.g. [WZnRu III 2(H 2 O) 2 (B-α-ZnW 9 O 34 ) 2 ] 10− ) have been studied 

intensely for their potentially asymmetric catalytic activity [225]. It remains to be seen if 

chiral, transition metal substituted derivatives of 14 can be prepared. Polyanion 14 was 

synthesized by interaction of In 3+ ions with the trilacunary precursor [B-α-PW 9 O 34 ] 9− in 

aqueous, acidic medium. We discovered that the trisubstituted 14 is obtained even in the 

presence of excess In 3+ ions. Additional studies are needed in order to explain why the 

tri- rather than the tetrasubstituted product is formed and also, why the vacancy is in an 

interior site. 

Solution NMR 

As polyanion 14 is diamagnetic we performed 183 W and 31 P NMR studies in solution. 

The 31 P NMR spectrum of 14 exhibits one signal at -11.4 ppm and the 183 W NMR spectrum 

shows 6 peaks at -98.3(1), -104.2(2), -128.6(2), -129.1(1), -133.1(2) and -186.6(1) 

ppm, respectively (see Figure 3.50). Initially this six-line pattern with intensity ratios 

2:2:2:1:1:1 may seem unexpected, but it can be rationalized as follows. The hypotheti- 

114

Table 3.13: Selected bond lengths and angles in polyanions 14 and 15 

14 15 

In1-O4I1 2.061(8) In1-O10I 2.087(9) 

In1-O7A 2.082(8) In1-O13A 2.115(9) 

In1-O5IN 2.133(7) In1-O15I 2.136(9) 

In1-O6I2 2.146(7) In1-O14A 2.165(9) 

In1-O4P 2.320(8) In1-O4P2 2.248(8) 

In1-O4P 2.323(7) In1-O4P2 2.274(8) 

In2-O8A 2.104(7) In2-O11I 2.120(9) 

In2-O9A 2.118(7) In2-O14A 2.126(8) 

In2-O6I2 2.139(7) In2-O12I 2.126(9) 

In2-O5IN 2.147(7) In2-O15I 2.134(8) 

In2-O4P 2.287(7) In2-O4P2 2.224(9) 

In2-Cl1 2.418(3) In2-Cl1 2.394(6) 

O4I1-In1-O7A 95.7(3) O10I-In1-O13A 94.5(4) 

O4I1-In1-O5IN 101.7(3) O10I-In1-O15I 98.6(3) 

O7A-In1-O5IN 87.6(3) O13A-In1-O15I 87.3(3) 

O4I1-In1-O6I2 86.1(3) O10I-In1-O14A 87.6(3) 

O7A-In1-O6I2 100.2(3) O13A-In1-O14A 99.7(3) 

O5IN-In1-O6I2 168.5(3) O15I-In1-O14A 170.3(3) 

O4I1-In1-O4P 175.8(3) O10I-In1-O4P2 175.2(3) 

O7A-In1-O4P 88.1(3) O13A-In1-O4P2 90.3(3) 

O5IN-In1-O4P 80.3(3) O15I-In1-O4P2 81.9(3) 

O6I2-In1-O4P 91.4(3) O14A-In1-O4P2 91.3(3) 

O4I1-In1-O4P 88.1(3) O10I-In1-O4P2 88.9(3) 

O7A-In1-O4P 176.2(3) O13A-In1-O4P2 176.5(3) 

O5IN-In1-O4P 91.9(3) O15I-In1-O4P2 91.3(3) 

O6I2-In1-O4P 79.7(3) O14A-In1-O4P2 81.4(3) 

O4P-In1-O4P 88.1(3) O4P2-In1-O4P2 86.3(3) 

O8A-In2-O9A 94.4(3) O11I-In2-O14A 89.8(3) 

O8A-In2-O6I2 165.3(3) O11I-In2-O12I 91.6(3) 

O9A-In2-O6I2 88.7(3) O14A-In2-O12I 169.7(3) 

O8A-In2-O5IN 88.7(3) O11I-In2-O15I 169.5(3) 

O9A-In2-O5IN 167.4(3) O14A-In2-O15I 87.2(3) 

O6I2 In2 O5IN 85.4(3) O12I-In2-O15I 89.6(3) 

O8A In2 O4P 85.1(3) O11I-In2-O4P2 87.1(3) 

O9A In2 O4P 87.3(3) O14A-In2-O4P2 83.4(3) 

O6I2 In2 O4P 80.7(3) O12I-In2-O4P2 86.5(3) 

O5IN In2 O4P 80.8(3) O15I-In2-O4P2 82.6(3) 

O8A In2 Cl1 92.4(2) O11I-In2-Cl1 89.0(3) 

O9A In2 Cl1 89.30(19) O14A-In2-Cl1 98.7(3) 

O6I2 In2 Cl1 101.96(19) O12I-In2-Cl1 91.5(3) 

O5IN In2 Cl1 102.80(19) O15I-In2-Cl1 101.4(3) 

O4P In2 Cl1 175.6(2) O4P2-In2-Cl1 175.5(3) 

cal, tetrasubstitued derivative [In 4 Cl 2 4(B-α-PW 9 O 34 ) 2 ] 8− has C 2h symmetry and would 

therefore be expected to show five lines in 183 W-NMR with intensity ratios 2:2:2:2:1. Indeed, 

we have obtained exactly this pattern for the tetrasubstituted, isostructural Zn(II) 

and Cd(II) derivatives [M 4 (H 2 O) 2 (B-α-GeW 9 O 34 ) 2 ] 12− (M = Zn 2+ , Cd 2+ ).[195] Removal 

of one of the inner indium atoms from [In 4 Cl 2 (B-α-PW 9 O 34 ) 2 ] 8− results in 14 with C 2 

point group symmetry. Consequently, 9 peaks are expected in 183 W NMR. However, close 

inspection of the structure of 14 (see Figure 3.50) indicates that the three tungsten atoms 

in the Keggin cap and four of the six tungsten atoms in the Keggin belt are not likely 

to be affected significantly by removal of an inner indium atom as they do not share oxo 

ligands with that indium atom. The inner indium atoms are coordinated to only three 

115

Fig. 3.50: 183 W NMR spectrum of [In 3 Cl 2 (B-α-PW 9 O 34 ) 2 ] 11− 

oxo groups of each Keggin half-unit, involving two belt tungsten atoms (W6, W7) and 

the phosphorus hetero atom. The six-line 183 W NMR spectrum of 14 with intensity ratios 

2:2:2:1:1:1 indicates that only one of these two belt tungsten atoms is significantly 

affected by removal of an inner indium atom. Clearly, this must be W7 which experiences 

a major change in its coordination sphere as a result of In atom removal. Before, it has 

only one terminal oxo ligand and after it has two terminal, cis-related oxo ligands. The 

dimeric polyanion [In 3 Cl 2 (P 2 W 15 O 56 ) 2 ] 17− 15 represents the Wells-Dawson analog of 10 

(see Figure 3.51). 

Fig. 3.51: Combined polyhedral/ball and stick representation of [In 3 Cl 2 (P 2 W 15 O 56 ) 2 ] 17− 15. The color 

code is the same as in Figure 3.40 

116

Polyanion 15 contains three indium centers sandwiched in between two trilacunary 

(P 2 W 15 O 56 ) units and one of the inner positions is vacant. In analogy to 15 the terminal 

ligands of the outer indium atoms in 15 are also chloride ions. As a result, polyanion 

15 exhibits also C 2 point group symmetry and is therefore chiral. The bond lengths 

and angles associated with the central indium-oxo fragment of 15 are shown in Table 

3.13. Some other trisubstituted analogs of 15 exist, but in all cases the ‘vacant’ 

site is in an outer position and it is occupied by a sodium ion in the solid state (e.g. 

[Fe 2 (FeOH 2 )(NaOH 2 )(P 2 W 15 O 56 ) 2 ] 14− ) [219]. Polyanion 15 was synthesized by interaction 

of In 3+ ions with the trilacunary precursor [P 2 W 15 O 56 ] 12− in aqueous, acidic medium. 

We discovered that the trisubstituted 15 is formed even in the presence of excess In 3+ 

ions. As polyanion 15 is diamagnetic we performed 183 W and 31 P NMR studies in solution. 

The latter exhibits two signals of equal intensity at -7.1 and -13.3 ppm, respectively, 

which is in agreement with the solid state structure. The two Wells-Dawson fragments 

in 15 are equivalent and they contain two P atoms each. The signal at -7.1 ppm can be 

assigned to the P-atom closer to the indium-core, whereas the signal at -13.3 ppm corresponds 

to the more distant P-atom. The 183 W NMR spectrum of 15 is expected to show 

around 9-10 peaks (based on the arguments used above for 14) and we see this number 

of signals between -80 and -240 ppm. However, the poor signal-to-noise ratio of our spectrum 

did not allow us to identify all peaks unequivocally. Although polyanions 14 and 

15 are chiral they have crystallized as a racemic mixture. Our crystallographic studies 

have revealed that both inner indium positions are occupied, but only with occupancy 

factors of 0.5 each. This means that individual molecules of 14 and 15 contain only one 

indium atom in one of the two possible inner positions. As the synthesis procedure of 14 

and 15 is not stereoselective, both enantiomers are formed in equal amounts. Apparently 

the crystallization process is also not stereoselective, which is not a surprise as the chiral 

site in 14 and 15 is somewhat hidden by the two Keggin caps and as a result is not 

expected to influence polyanion packing significantly. Therefore, both enantiomers orient 

randomly within the solid state lattices of NH4-14 and NH4Na-15 leading to the crystallographic 

observations described above.The indium-substituted, lone pair containing 

polyoxoanions [In 4 (H 2 O) 10 (β -AsW 9 O 32 OH) 2 ] 4− (16) and [In 4 (H 2 O) 10 (β-SbW 9 O 33 ) 2 ] 6− 

117

(17) are isostructural. They consist of two β-XW 9 (X = As III , Sb III ) Keggin moieties 

linked by four In 3+ ions resulting in a structure with idealized C 2h symmetry (see Figure 

3.52). 

Fig. 3.52: Combined polyhedral/ball and stick representation of 

[In 4 (H 2 O) 10 (β-AsW 9 O 32 OH) 2 ] 4− (16) and [In 4 (H 2 O) 10 (β-SbW 9 O 33 ) 2 ] 6− (17). The WO 6 octahedra are 

shown in red and the balls represent indium (green), arsenic/antimony (blue) and water molecules (red). 

The four In 3+ ions consist of two inequivalent pairs, the inner two In 3+ ions have 

two terminal H 2 O ligands and the outer two In 3+ ions have three terminal H 2 O ligands. 

Polyanions 16 and 17 were synthesized in aqueous acidic medium (pH 2) from interaction 

of In 3+ ions with the lacunary Keggin precursors [α-AsW 9 O 33 ] 9− and [ α-SbW 9 O 33 ] 9− , 

respectively. Therefore the mechanism of formation of 16 and 17 involves insertion, 

isomerization (α → β) and dimerization. The bond lengths and angles associated with 

the central indium-oxo fragments of 16 and 17 are shown in Table 3.14 

183 W NMR on freshly synthesized solutions of RbNa-16 resulted in five peaks (relative 

intensities in parenthesis) at -102.3(1), -109.6(2), -153.7(2), -171.3(2) and -199.2(2) ppm, 

respectively (see Figure 3.53). 

This result indicates that in solution a species with C 2h symmetry is present, which 

is in complete agreement with the solid state structure of RbNa-16. Furthermore, the 

NMR spectrum does not change even after several weeks, indicating the high stability 

118

Table 3.14: Selected bond lengths and angles in polyanions 16 and 17 

16 17 

In(1)-O(3I1) 2.069(8) In(1)-O(3IN) 2.083(11) 

In(1)-O(7I1) 2.073(7) In(1)-O(6IN) 2.109(10) 

In(1)-O(6T)#1 2.107(7) In(1)-O(9B)#2 2.120(10) 

In(1)-O(6I1) 2.109(7) In(1)-O(1I1) 2.146(10) 

In(1)-O(2WI) 2.192(8) In(1)-O(3I1) 2.164(12) 

In(1)-O(1WI) 2.206(8) In(1)-O(2I1) 2.193(12) 

In(2)-O(4I2) 2.084(7) In(2)-O(1A)#2 2.059(10) 

In(2)-O(5I2) 2.112(7) In(2)-O(5IN) 2.072(11) 

In(2)-O(4WI) 2.153(8) In(2)-O(9IN) 2.110(11) 

In(2)-O(5WI) 2.156(8) In(2)-O(9A)#2 2.117(10) 

In(2)-O(6I2) 2.160(8) In(2)-O(2I2) 2.170(12) 

In(2)-O(3WI) 2.206(9) In(2)-O(1I2) ) 2.174(11) 

As(1)-O(3AS) 1.794(7) Sb(1)-O(2SB) 1.989(9) 

As(1)-O(1AS) 1.810(7) Sb(1)-O(1SB) 2.014(10) 

As(1)-O(2AS) 1.814(7) Sb(1)-O(3SB) 2.014(10) 

O(3I1)-In(1)-O(7I1) 173.8(3) O(3IN)-In(1)-O(6IN) 86.1(4) 

O(3I1)-In(1)-O(6T)#1 89.4(3) O(3IN)-In(1)-O(9B)#2 99.4(4) 

O(7I1)-In(1)-O(6T)#1 95.0(3) O(6IN)-In(1)-O(9B)#2 95.6(4) 

O(3I1)-In(1)-O(6I1) 92.3(3) O(3IN)-In(1)-O(1I1) 95.3(4) 


O(6T)#1-In(1)-O(6I1) 92.4(3) O(9B)#2-In(1)-O(1I1) 86.7(4) 

O(3I1)-In(1)-O(2WI) 84.7(3) O(3IN)-In(1)-O(3I1) 174.4(4) 


O(6T)#1-In(1)-O(2WI) 172.0(3) O(9B)#2-In(1)-O(3I1) 86.2(4) 

O(6I1)-In(1)-O(2WI) 93.2(3) O(1I1)-In(1)-O(3I1) 84.6(4) 



O(6T)#1-In(1)-O(1WI) 86.8(3) O(9B)#2-In(1)-O(2I1) 166.1(4) 


O(2WI)-In(1)-O(1WI) 87.9(3) O(3I1)-In(1)-O(2I1) 82.5(5) 

O(4I2)-In(2)-O(5I2) 90.9(3) O(1A)#2-In(2)-O(5IN) 177.4(4) 

O(4I2)-In(2)-O(4WI) 91.6(3) O(1A)#2-In(2)-O(9IN) 92.2(4) 

O(5I2)-In(2)-O(4WI) 174.6(3) O(5IN)-In(2)-O(9IN) 90.0(4) 

O(4I2)-In(2)-O(5WI) 175.2(3) O(1A)#2-In(2)-O(9A)#2 89.6(4) 

O(5I2)-In(2)-O(5WI) 90.0(3) O(5IN)-In(2)-O(9A)#2 89.0(4) 

O(4WI)-In(2)-O(5WI) 87.2(3) O(9IN)-In(2)-O(9A)#2 88.8(4) 

O(4I2)-In(2)-O(6I2) 96.0(3) O(1A)#2-In(2)-O(2I2) 94.3(4) 


O(4WI)-In(2)-O(6I2) 85.7(3) O(9IN)-In(2)-O(2I2) 173.5(4) 

O(5WI)-In(2)-O(6I2) 88.5(3) O(9A)#2-In(2)-O(2I2) 90.3(4) 

O(4I2)-In(2)-O(3WI) 93.3(3) O(1A)#2-In(2)-O(1I2) 88.1(4) 


O(4WI)-In(2)-O(3WI) 84.1(3) O(9IN)-In(2)-O(1I2) 94.4(4) 

O(5WI)-In(2)-O(3WI) 82.0(3) O(9A)#2-In(2)-O(1I2) 176.2(4) 


O(3AS)-As(1)-O(1AS) 98.9(3) O(2SB)-Sb(1)-O(1SB) 90.7(4) 



of RbNa-16 in aqueous solution. The 183 W NMR behavior of the antimony derivative 

KNa-17 is apparently more complex and requires additional studies. Our preliminary 

results on freshly synthesized solutions of KNa-17 resulted in six peaks at -80.9, -99.5, 

-117.5, -133.9, -160.6 and -176.7 ppm. Very recently Krebs et al. reported on the solid 

state structures of the closely related compounds Na 5n H 2n [(In(H 2 O) 2 ) 1.5 (Na(H 2 O) 2 ) 0.5 

(In(H 2 O) 2 ) 2 (SbW 9 O 33 ) 2 ] n·28H 2 O and Na 2 K 2 H 2 [(In(H 2 O) 3 ) 2 (In(H 2 O) 2 ) 2 (AsW 9 O 33 ) 2 ]·37H 2 O 

[30]. Although the solid state structures of ‘Krebs’ compounds and ours are different, 

119

Fig. 3.53: 183 W NMR spectrum of [In 4 (H 2 O) 10 (β-AsW 9 O 32 OH) 2 ] 4− at 293 K 

the latter contains a polyanion identical to 16. On the other hand, the antimony(III)- 

containing polyanion of Krebs et al. is different from 17 as the outer indium positions 

are partially (25%) occupied by sodium ions resulting in a polymeric solid state structure. 

Bond valence sum (BVS) calculations on 16 and 17 resulted in the conclusion that all 

terminal ligands of the indium atoms are water molecules [85]. For 17 we could not identify 

any other protonation sites, but for 16 we noticed that two In-O-W bridging oxygens 

(O5I2, O5I2’) are actually hydroxo groups. This results in a charge of -4 for 16 and -6 for 

17, which is somewhat surprising as both species were synthesized at exactly the same 

pH. It is of interest to compare the synthetic conditions for the preparation of ‘Krebs 

and our compounds. Besides using a higher concentration of the reagents (by about a 

factor of 2), Krebs and coworkers also performed their syntheses at pH 6.5-7, whereas we 

worked in much more acidic medium (pH 2.0). We used such acidic conditions because 

former work of Krebs et al. and also our own has demonstrated that [α-XW 9 O 33 ] 9− and 

[β-XW 9 O 33 ] 9− (X = As III , Sb III ) are in equilibrium in aqueous solution [33, 39, 69, 83]. 

The former dominates in neutral medium whereas the latter is present in acidic solution. 

Our synthetic conditions of 16 and 17 are in full agreement with this, as both species 

are formed easily in acidic medium. The recent results of Krebs et al. indicate that 16 

is also stable in the neutral pH range, but this is apparently not the case for 17. This 

observation combined with the different degree of protonation for 16 and 17 deserves 

attention and is further supported by our 183 W-NMR studies (see 3.53). We have already 

observed previously that the products resulting from interaction of transition metal 

ions with [α-AsW 9 O 33 ] 9− and [α-SbW 9 O 33 ] 9− are not solely determined by the pH, but 

120

also by the type of transition metal ion and its preferred coordination geometry. For 

example, we were able to synthesize the Fe 3+ analogues of 16 and 17, but not the Cu 2+ 

and Zn 2+ derivatives.[39, 83] Reaction of the latter metal ions with [α-XW 9 O 33 ] 9− (X = 

As III , Sb III ) resulted in the polyanions [M 3 (H 2 O) 3 (α-XW 9 O 33 ) 2 ] 12− (M = Cu 2+ , Zn 2+ ; 

X = As III , Sb III ), no matter what the pH. The Cu 2+ and Zn 2+ ions have a square pyramidal 

coordination geometry in this structure, whereas the coordination geometry of all 

four In 3+ ions in 16 and 17 is octahedral. Interestingly, Cr 3+ was the only other firstrow 

transition metal ion besides Fe 3+ for which we could synthesize the tetra-substituted 

structure with As III and Sb III as hetero atoms [83]. It becomes apparent, that all three 

ions which allow formation of this structural type are trivalent (In 3+ , Fe 3+ , Cr 3+ ). However, 

by using Se IV and Te IV as hetero atoms we could also incorporate divalent transiton 

metal ions (e.g. Mn 2+ , Co 2+ , Ni 2+ , Zn 2+ , Cd 2+ , Hg 2+ ) [83]. These results indicate that 

the tetra-substituted Krebs-type structure is most stable within the charge limits of -4 

and -8. The differences of 12A and 12B in their solution and solid state properties (e.g. 

protonation, charge, pH-dependent stability) led us to check if the different hetero atoms 

(As III , Sb III ) perhaps initiate small structural changes (e.g. bond lengths, angles) in the 

polyanions. As expected, the As-O bond lengths are shorter than the Sb-O bonds (see 

Table 3.13.) and the observed hetero atom separations X···X within 16 (As···As = 6.26 

Å) and 17 (Sb···Sb = 5.87 Å) are fully consistent with this. On the other hand, the type 

of hetero group has no significant effect on the W-O and In-O bond lengths in 16 and 17 

(see Table 3.13). Therefore we conclude that there are no obvious structural differences in 

16 and 17. Furthermore, there is no significant lone-pair/lone-pair repulsion involving the 

lone pairs of the two hetero atoms. Both conclusions are fully consistent with our observations 

on the iron(III)-substituted derivatives of 16 and 17.[83] In fact, the hetero atom 

separations in 16 and 17 (see above) are even larger than in [Fe 4 (H 2 O) 10 (β-AsW 9 O 33 ) 2 ] 6− 

(As···As = 6.03 Å) and in [Fe 4 (H 2 O) 10 (β-SbW 9 O 33 ) 2 ] 6− (Sb···Sb = 5.68 Å), which reflects 

the larger In-O bond lengths compared to Fe-O (the ionic radii of In 3+ and Fe 3+ are 0.94 

Å and 0.79 Å, respectively). 

121

3.12.4 Conclusion 

We have synthesized and structurally characterized four novel indium(III)-substituted, 

sandwich-type polyoxoanions. The tri-indium substituted tungstophosphates [In 3 Cl 2 (Bα-PW 

9 O 34 ) 2 ] 11− 14 and [In 3 Cl 2 (P 2 W 15 O 56 ) 2 ] 17− 15 belong to the class of Weakley-type 

sandwich polyanions and they represent the first indium-containing derivatives. Polyanions 

14 and 15 are also stable in solution as indicated by a one-line (1) and a two-line 

(2) 31 P NMR pattern. The most important structural feature of 14 and 15 is the fact 

that they are chiral (C 2 symmetry), which results from a vacancy in one of the inner 

indium positions. Therefore 14 and 15 are of interest for catalytic and medicinal applications. 

Currently we investigate if chiral, transition metal substituted derivatives 

of 14 and 15 can be formed. The lone pair containing, tetra-indium substituted polyoxotungstates 

[In 4 (H 2 O) 10 (β-AsW 9 O 32 OH) 2 ] 4− 16 and [In 4 (H 2 O) 10 (β-SbW 9 O 33 ) 2 ] 6− 17 

belong to the class of Krebs-type sandwich polyanions. Polyanions 16 and 17 consist of 

two B-β-(XW 9 O 33 ) (X = As III , Sb III ) Keggin moieties linked via four octahedral indium 

atoms leading to a dimeric structure with nominal C 2h symmetry. Polyanion 16 is also 

stable in solution as indicated by a five-line pattern (1:2:2:2:2) in 183 W-NMR. We have 

also synthesized the Se(IV) and Te(IV) analogues of 16 and 17. 

122

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128

APPENDIX

NMR Spectra 

Fig. 3.54: 13 C NMR spectrum of polyanion 1 

130


131

Fig. 3.56: 31 P NMR spectrum of polyanion 3 

132

Fig. 3.57: 119 Sn NMR spectrum of polyanion 3 

133


134

Fig. 3.59: 1 H NMR spectrum of polyanion 3 

135


136


137



138



139



140

Fig. 3.68: 183 W NMR spectrum of polyanion 7 


141


Fig. 3.71: 119 Sn NMR spectrum of polyanion 8 in presence of sodium chloride 

142

Incomplete Results 

1-The hybrid organic-inorganic 1-D material: {K 7 [{Sn(CH 3 ) 2 } 3 (H 2 O) 2 (PW 9 O 36 )]} ∞ 

Experimental 

Preparation of {[{Sn(CH 3 ) 2 } 3 (H 2 O) 2 (PW 9 O 36 )] 7− } ∞ (18): A 1.46 g (0.600 mmol) sample 

of Na 9 [A-PW 9 O 34 ] [73] was added with stirring to a solution of 0.435 g (1.98 mmol) 

(CH 3 ) 2 SnCl 2 in 20 mL H 2 O. The pH was adjusted to 6 by addition of 1 M NaOH solution. 

This solution was heated to ∼80 ◦ C for 1 hour and then cooled to room temperature and 

filtered. Addition of 0.5 mL of 1.0 M KCl solution to the colorless filtrate and slow 

evaporation at room temperature led to a white crystalline product after about a week 

or two. FTIR spectroscopy: 1065(s), 1007(m), 935(s), 914(sh), 837(m), 789(s), 656(s), 

593(w), 575(w), 515(m) cm −1 . 

Fig. 3.72: FTIR spectra of compound K-18(red) and Na 9 [A-PW 9 O 34 ](blue) 







143




Empirical formula W 36 Sn 8 P 4 K 8 C 16 O 188 

fw 11205 


a (Å) 12.3879(8) 

b (Å) 14.1573(9) 

c (Å) 32.6941(20) 

β ( ◦ ) 90.826(1) 

vol (Å 3 ) 5733.3(63) 

Z 4 

temp ( ◦ C) -110 


d calcd (mg m −3 ) 3.25 

abs coeff. (mm −1 ) 20 

R [I > 4 σ(I)] a 0.113 



Solution NMR 

Polyanion 18 is diamagnetic and contains four spin 1 nuclei 2 (183 W, 119 Sn, 13 C, 1 H) and 


We examined the solution properties of 18 by 31 P NMR (D 2 O, ∼20 ◦ ). Our 31 P NMR 

measurements resulted in one singlet at (-12.3 ppm). Further solution NMR of differerent 

nuclei are to be done. 

HPPS measurement 

The dynamic light scattering measurements was done on a freshly prepared solution of 

polyanion 18 in collaboration with Prof. M. Winterhalter and his group (IUB, Germany). 

High performance particle sizer(HPPS) provided by Malvern instruments, suggest that 

the particle were monodispersed. The size distribution by intensity showed two kinds 

of particle, a size of diameter 3.1 nm and 284 nm but size distribution by number and 

144

Fig. 3.73: 31 P NMR spectrum of polyanion 18 

volume suggest that the particle of size 3.1 nm is more populated. 

All the measurement were done in aqueous medium in a polystyrene cuvette. 

Fig. 3.74: Size distribution by intensity of polyanion 18 


The structure of the polyanion 18 can be best described as a 1-D polymeric composed of 

monopolyanionic building blocks ({{Sn(CH 3 ) 2 } 3 }(H 2 O) 2 (α-PW 9 O 36 ) 7− ) that are linked 

via Sn-O-(W’) bridges. The three organo-tin groups attached to each monomeric unit 

of 18 contain tin centers that are octahedrally coordinated by four oxygen atoms and 

two methyl groups and two water molecules. Furthermore the two methyl groups on 

145

Fig. 3.75: Size distribution by number of polyanion 18 

Fig. 3.76: Size distribution by volume of polyanion 18 

each tin atom are positioned trans to each other. All the tin centers are grafted on 

the A-type [PW 9 O 34 ] 9− via coordination to the terminal oxygen atoms of the two edgeshared 

octahedra. Out of the three dimethyltin units, two tin atoms are coordinated to 

the neighboring polyanion by 2Sn-O-(W’) bridges and one tin atom possess two water 

molecules as terminal ligands. Bond-valence-sum (BVS) calculations for 18 indicated 

Fig. 3.77: Ball/stick and polyhedron representation of solid state of 18 showing 1-D chain 

that no oxygen of the building blocks (PW 9 O 34 ) caps is protonated [85]. 

146

2-The hybrid organic-inorganic 1-D material:(K 10 [{Sn(CH 3 ) 2 } 2 (P 2 W 12 O 48 )]) ∞ 

Experimental 

Preparation of ({[{Sn(CH 3 ) 2 } 2 (P 2 W 12 O 48 )]} 10− ) ∞ (19): A 2.36 g (0.600 mmol) sample 

of K 12 [H 2 P 2 W 12 O 48 ] [75] was added with stirring to a solution of 0.435 g (1.98 mmol) 

(CH 3 ) 2 SnCl 2 in 20 mL H 2 O. The pH was adjusted to 6 by addition of 1 M NaOH solution. 

This solution was heated to ∼50 ◦ C for 30 minutes and then cooled to room temperature 

and filtered. Addition of 0.5 mL of 1.0 M KCl solution to the colorless filtrate and slow 

evaporation at room temperature led to a white crystalline product after about a week or 

two. FTIR spectroscopy: 1129(m), 1084(s), 1052(w), 1016(m), 940(vs), 917(vs), 885(sh), 

804(vs), 732(vs), 566(sh), 522(w), 463(w) cm −1 . 

Fig. 3.78: FTIR spectra of compound K-19(red) and K 12 [H 2 P 2 W 12 O 48 ](blue) 









147


Empirical formula W 48 Sn 8 P 8 K 36 O 264 C 16 H 48 

fw 11205 

space group (No.) C 2/c (15) 

a (Å) 14.5700(14) 

b (Å) 24.3039(14) 

c (Å) 20.4474(14) 

β ( ◦ ) 100.682(2) 

vol (Å 3 ) 7115.12(3) 

Z 4 

temp ( ◦ C) -110 


d calcd (mg m −3 ) 3.71 

abs coeff. (mm −1 ) 20.38 

R [I > 2 σ(I)] a 0.051 




The structure of polyanion 19 is best described as a polymer composed of monopolyanionic 

building blocks ({{Sn(CH 3 ) 2 } 2 }(H 2 O) 2 [H 2 P 2 W 12 O 48 ] 10− ) that are linked via Sn-O-(W’) 

bridges. This arrangement leads to a 1-D polymeric chain. The two organo-tin groups 

attached to each monomeric unit of 19 contain tin centers that are five coordinated 

by two methyl groups and three oxo groups, respectively. Furthermore the two methyl 

groups on each tin atom are positioned trans to each other and all the organotin groups 

are structurally equivalent. The tin atoms are connected to the adjacent polyanion by 

a single Sn-O-(W’) bridges in such a way that they are coordinated to two terminal 

oxygens of the cap of the (H 2 P 2 W 12 O 48 ) fragment and one terminal oxygen of the belt 

of the adjacent polyanion. Alternatively 19 can be best described as described as a 

hexalacunary [H 2 P 2 W 12 O 48 ] 12− fragment which has taken up two (CH 3 ) 2 Sn 2+ units. All 

the tin atoms are five coordinated (trigonal pyramidal) and all the methyl groups are 

trans to each other. All the tin atoms are coordinated to the neighboring polyanion by 

single Sn-O-(W’) bridge. Bond-valence-sum (BVS) calculations for 19 indicated that no 

oxygen of the building blocks (H 2 P 2 W 12 O 48 ) caps is protonated [85]. 

148

Fig. 3.79: Ball/stick and polyhedron representation of solid state of 19 showing 1-D chain 

3-The cyclic trimeric-titanium substituted, tungstophosphate: 

[{Ti 3 O(A-α-PW 9 O 37 )(OH)} 3 ] 10− 

Experimental 

The precursor K 14 [P 2 W 19 O 69 (H 2 O)] was synthesized according to the published procedure 

of Tourné et al. and the purity was confirmed by infrared spectroscopy [80]. All 

other reagents were used as purchased without further purification. K 10 [{Ti 3 O(A-α- 

PW 9 O 37 )(OH)} 3 ] (K-20). The title compound was synthesized by dissolving 0.141 g 

(0.88 mmols) of TiO(SO 4 ) in 40 mL potassium acetate buffer followed by addition of 2.26 

g (0.40 mmols) K 14 [P 2 W 19 O 69 (H 2 O)]. This solution (pH 4.8) was heated to ∼80 ◦ C for 

1 h and then cooled to room temperature. 2 mL of 30% H 2 O 2 was added to the solution. 

The color of the solution changed to golden yellow. The solution was filtered and a 1 mL 

of 0.1 M NH 4 Cl solution were added and then the solution was allowed to evaporate in 

an open vial at room temperature. A white crystalline product started to appear after a 

week or two. Evaporation was continued until the solvent approached the solid product. 

FTIR spectra for K 10 [{Ti 3 O(A-α-PW 9 O 37 )(OH)} 3 ] : 1165(sh), 1064(s), 1031(w), 959(s), 

882(w), 783(s), 668(s), 652(s), 617(w), 587(sh) cm −1 . The FTIR spectrum was recorded 

on a Nicolet Avatar FTIR spectrophotometer in a KBr pellet. 





149

Fig. 3.80: FTIR spectra of compound K-20(red) and K 14 [P 2 W 19 O 69 (H 2 O)](blue) 






Empirical formula K 45 O 369 P 9 Ti 27 W 81 

fw 15507.27 


a (Å) 29.8461(7) 

c (Å) 13.6781(8) 

volume (Å 3 ) 10551.9(8) 

Z 3 

temp. ( ◦ C) -100 


dcalc (mg m −3 ) 2.440 

abs. coeff. (mm −1 ) 15.72 

R [I > 2 σ(I)] a 0.071 




The novel polyanion 20 is isostructural to the polyanion 10. The polyanion 20 is composed 

of three [A-α-PW 9 O 34 ] units and nine TiO 6 octahedra. The nine TiO 6 octahedra 

150

Fig. 3.81: Ball/stick and polyhedral representation of polyanion 20 

are connected to each other by Ti-O-Ti bridges. Three TiO 6 octahedra of each trilacunary 

[A-α-PW 9 O 34 ] unit fills the lacuna to form a complete Keggin cluster. Of the 

three TiO 6 octahedra two are connected to Ti-centers of adjacent polyanions by Ti-O-Ti 

bridges, the unique TiO 6 octahedra in each Keggin subunit has terminal hydroxoligand. 

Bond-valence-sum (BVS) calculations for polyanion 20 indicated that the unique Ti is 

monoprotonated no oxygen of the building blocks [A-α-PW 9 O 34 ] caps is protonated [85]. 

The polyanion has a nominal symmetry of C 3v (see Figure. 3.74 

Catalytic studies are on progress by our collaborator Prof. O. A. 

Kholdeeva, Boreskov Institute Catalysis, Novosibirsk, Russia. 

151

FIRASAT HUSSAIN 

International University Bremen 

Campus Ring 8, Res. III, Room 110 

Bremen, D-28759, Germany. 

Curriculum Vitae 

Education 

Ph.D. (Chemistry), May 2006, International University Bremen, Germany. 

Advisor: Prof. Ulrich Kortz, International University Bremen. 

M.Phil. (Chemistry), 2001, Utkal University, India. 

M.S. (Chemistry), 2000, Utkal University, India. 

B.S. (Physics, Chemistry and Mathematics), 1998, Sambalpur University, Orissa, India. 

Research Experience 

Research Scholar, International University Bremen, Germany, 01/2003- 31/2005 

• Synthesized novel hybrid inorganic-organic polyoxoanions based on dimethyltin. 

• Synthesized novel supramolecular inorganic-organic polyoxoanions based on dimetyltin. 

• Synthesized titanium, indium, cadmium and copper containing novel poloxoanions. 

Research Assistant, Indian Institute of Technology, Bombay, India. 12/2001- 

03/2003 

• Synthesized and studied the catalytic properties of titanium and chromium containing 

hexagonal mesoporous aluminophosphates. 

• Synthesized Al-, Ga-containing novel mesoporous MCM-48 molecular sieves. These 

catalysts tested for the vapour phase phenol alkylation. 

Personal Information 

Indian,unmarried and born on 19 th February, 1975, in Bhawanipatna (Orissa), India. 

152

Teaching Experience 

At International University Bremen, Bremen, Germany 

Teaching Assistant - (4 semesters) Tutorials For B.S. student in General Chemistry and 

laboratory. For a semester Physical Chemistry laboratory 

Instrumentations known 

Experienced in handling different essential analytical tools(XRD, UV-vis spectroscopy, 

infrared spectroscopy, Multi nuclear NMR required for characterization of polyoxoanions. 

Conservant with other analytical techniques ( Vapour phase reactor, Thermal techniques 

(TG-DTA) Transmission electron microscopy. 

Computer skills 

Softwares: Diamond crystallographic software, Origin, Delta software for NMR, Latex 

and MSOffice, ChemDraw, photoshop. 

Academic Honours 

• (i)Qualified - Graduate Aptitude Test In Engineering (GATE) 90.43, Conducted by 

Indian Institute of Technology, India, 2000. 

• (ii) Gold Medalist for outstanding performance in M.Phil in Chemistry. 

• (iii) 5th position in the University for B.S. 

Hobbies 

Cricket, Table tennis, Soccer, Reading, Watching television and listening to music. 

153

Publications 

1. Observation of a Half Step Magnetization in the (Cu 3 )-Type Triangular Spin Ring 

K.-Y. Choi, Y. H. Matsuda, H. Nojiri*, U. Kortz*, F. Hussain, A. C. Stowe, C. 

Ramsey, N. S. Dalal*, Phys. Rev. Lett., 2006, 96, 107202. 

2. STM/STS Observation of Polyoxoanions on HOPG Surfaces: The Wheel-shaped 

[Cu 20 Cl(OH) 24 (H 2 O) 12 (P 8 W 48 O 184 )] 25− and the Ball-shaped 

[{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-PW 9 O 34 ) 12 ] 36− 

M. S. Alam, V. Dremov, P. Müller*, A. V. Postnikov, S. S. Mal, F. Hussain, U. 

Kortz*, Inorg. Chem., 2006, 45, 2866-2872. 

3. Tetrakis-Dimethyltin Containing Tungstophosphate [{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ] 28− : 

First Evidence for Lacunary Preyssler Ion 

F. Hussain, U. Kortz*, B. Keita, L. Nadjo*, M. T. Pope, Inorg. Chem., 2006, 45, 

761-766. 

4. Ball-Shaped Heteropolytungstates [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 (A-XW 9 O 34 ) 12 ] 36− 

(X = P V , As V ) 

U. Kortz*, F. Hussain, M. Reicke, Angew. Chem. Int. Ed. 2005, 44, 3773-3777. 

5. Structure and Solution Properties of the Cadmium(II)-Substituted Tungstoarsenate 

[Cd 4 Cl 2 (B-α-AsW 9 O 34 ) 2 ] 12− 

F. Hussain, L. Bi, U.Rauwald, M. Reicke and U. Kortz*, Polyhedron, 2005, 24, 

847-852. 

6. Polyoxoanions Functionalized By Diorganotin Groups: The Tetrameric, 

Chiral Tungstoarsenate(III) [{Sn(CH 3 ) 2 (H 2 O)} 2 {Sn(CH 3 ) 2 }As 3 (α-AsW 9 O 33 ) 4 ] 21− 

F. Hussain and U. Kortz*. Chem. Commun., 2005, 1191-1193. 

7. Some Indium(III)-Substituted Polyoxotungstates of the Keggin and Dawson Type 

F. Hussain, M. Reicke, V. Janowski, S. de Silva, J. Futuwi, U. Kortz* Comptes 

Rendus Chimie, 2005, 8, 1045-1056. 

154

8. A Novel Isopolytungstate Functionalized by Ruthenium:[HW 9 O 33 Ru II 

2 (dmso) 6 ] 7− 

L. Bi, F. Hussain, U. Kortz*, M. Sadakane, M. H. Dickman, Chem. Commun., 

2004, 1420. 

9. Structural Control on the Nanomolecular Scale: Self-Assembly of The Polyoxotungstate 

Wheel [(β-Ti 2 SiW 10 O 39 ) 4 ] 24− 

F. Hussain,B. S. Bassil, L. Bi, M. Reicke, U. Kortz*. Angew. Chem. Int. Ed., 2004, 

43, 3485. 

10. The Bis-Phenyltin Substitued, Lone Pair Containing Tungstoarsenate 

[Na(H 2 O)(C 6 H 5 Sn) 2 As 2 W 19 O 67 (H 2 O)] 7− 

F. Hussain,U. Kortz*, R. J. Clark. Inorg. Chem., 2004, 43, 3237. 

11. Polyoxoanions Functionalized by Diorganotin Groups. 1. The Hybrid Organic- 

Inorganic 2-D material (CsNa 4 [{Sn(CH 3 ) 2 } 3 O(H 2 O) 4 (β-XW 9 O 33 )] ·5H 2 O) ∞ (X =As III , 

Sb III ) and its Solution Properties 

F. Hussain, M. Reicke, U. Kortz*. Eur. J. Inorg. Chem., 2004, 2733. 

12. Synthesis, characterization, and catalytic properties of chromium- containing hexagonal 

mesoporous aluminophosphate molecular sieves. 

S. K. Mohapatra, F. Hussain, P.Selvam* Catalysis Letters Vol. 85, Nos. 3-4, Feb. 

2003, 217-222. 

13. Titanium substituted hexagonal mesoporous aluminophosphates: Highly efficient 

and selective heterogeneous catalysts for the oxidation of phenols at room temperature. 

S.K. Mohapatra, F. Hussain, P. Selvam* Catalysis Communications 4, 2003, 57-62. 

155

PAPERS IN CONFERENCE/ SYMPOSIA / WORK- 

SHOPS 

1. F. Hussain, M. Reicke and U. Kortz*, Hybrid Organic-Inorganic Polyoxometalates 

functionalized by Organotin Moieties, Extended Abstract-7th Norddeutsches 

Doktoranden- Kolloqium der anorganisch-chemischen Institute, Organisation vom 

Institute fur Anorganische Chemie der Christian-Alberchts-Universitat zu Kiel, Hamburg, 

Germany, Sept 30-Oct 01, 2004, p12. 

2. F. Hussain, L. Bi, B. Bassil and U. Kortz*, Discrete Polyoxoanions: Nanomolecular 

structures with Multiple Functions, Extended Abstract-7th Norddeutsches 

Doktoranden- Kolloqium der anorganisch-chemischen Institute, Organisation vom 

Institute fur Anorganische Chemie der Christian-Alberchts-Universitat zu Kiel, Hamburg, 

Germany, Sept 30-Oct 01, 2004, p12. 

3. B. S. Bassil, F. Hussain, U. Kortz*, S. Nellutla, A. C. Stove, N. S. Dalal, Transition 

Metal Substituted Polyoxotungstates and Their Unique Magnetic Properties, 

Extended Abstract- Fourth International Conferences on Inorganic Materials, University 

of Antwerp, Belgium, September 19-21, 2004, P48. 

4. F. Hussain, L. Bi, B. Bassil and U. Kortz*, Discrete Polyoxoanions: Nanomolecular 

structures with Multiple Functions,Extended Abstract-7th Iinternational Conference 

on Nanostructured Materials, Wiesbaden, Germany, June 20-24, 2004, p.161 

5. F.Hussain and U.Kortz*, Novel Hybribs Of Inorganic-Organic Polyoxometalates, 

1st Open Graduate Students Conference, International University Bremen, Bremen. 

Germany. 

6. F. Hussain and P. Selvam*, Tertiary butylation of phenol over versatile solid acid 

catalysts H-GaMCM48, Extended Abstract-1st Indo-German Conference on Catalysis, 

IICT-Hyderabad, Feb 6-8, 2003, PO-32. 

156

CONFERENCE / SYNOPSIA / WORKSHOPS AT- 

TENDED 

1. 1st Indo-German Conference on Catalysis, February 6-8, 2003, IICT-Hyderabad,India. 

2. Conference on Electron Microscopy (EMSI), In-House Symposia February 19-22, 

2003, I.I.T. Bombay, Powai, India. 

3. 1st Open Graduate Students Conference, International University Bremen, Bremen, 

Germany, October 2003. 

4. 7th International Conference on Nanostructured Materials, Wiesbaden, Germany, 

June 20-24, 2004. 

5. Fourth International Conferences on Inorganic Materials, University of Antwerp, 

Belgium, September 19-21, 2004. 

6. Norddeutsches Doktoranden- Kolloqium der anorganisch-chemischen Institute, Organisation 

vom Institute fur Anorganische Chemie der Christian-Alberchts-Universitat 

zu Kiel, Hamburg, Germany, Sept 30-Oct 01, 2004, p12. 

157

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