Luis Fernando Piedra-Garza - Jacobs University

Hybrid Organic-Inorganic Polyoxotungstates 

Functionalized by Diorganotin and -antimony Linkers 

by 

Luis Fernando Piedra-Garza 

A thesis submitted in partial fulfilment of the requirements for the 

degree of: 

Doctor of Philosophy in Chemistry 

Approved Dissertation Committee: 

Prof. Dr. Ulrich Kortz (mentor, Jacobs University) 

Prof. Dr. Gerd-Volker Röschenthaler (Jacobs University) 

Prof. Dr. Hans-Joachim Breunig (Universität Bremen) 

Date of Defense: 7 th . of September, 2009. 

Jacobs University Bremen 

School of Engineering and Science

Dedicado a Don Rubén Piedra Niebla † y Doña Lupita 

Garza de Piedra; así como a mis hermanos Lety, Rubén 

y Ronald.

Acknowledgments 

The amount of people that contributed to this work, sometimes in unexpected 

ways and therefore to which I am sincerely obliged is indeed numerous. First I 

would like to thank the Jacobs University that was like a home for me through 

countless hours spent in the laboratories and office. To Professor Dr. Dr. h.c. 

Bernhard Kramer, Dean of the School of Engineering and Science I am deeply 

grateful for giving me the opportunity to carry out my doctoral studies in the 

university. 

Due to the innumerable exchange of emails, discussions related to research issues 

and even of private nature, guidance, patience and his amazing enthusiasm for 

polyoxometalate chemistry I am deeply grateful to Prof. Dr. Ulrich Kortz. 

To Dr. Michael Dickman I am also exceptionally grateful for teaching me so 

much about crystallography, also for the nice conversations about the American 

culture. I also want to thank Mr. Bernd von der Kammer for his support in the 

laboratory, as well as Mr. Andreas Suchopar who was always willing to help; I 

thank them also for their help in order to improve my German. 

My gratitude to all my colleagues; PhD students and Postdoctoral fellows. It was 

a great luck to work with them. Special thanks to Dr. Santiago Reinoso who 

taught me so much during my early time at Jacobs University. 

I would also like to thank Prof. Dr. Hans-Joachim Breunig from the University of 

Bremen and his students for providing us with organoantimony precursors and 

therefore contributing to a great extent to the section devoted to organoantimony 

functionalized polyoxotungstates in the present work. 

i

En primer lugar a mi Padre Todopoderoso que nunca me dejó solo; a Don Rubén, 

donde quiera que esté ojalá esté un poco orgulloso de su huesito. A Doña “Pita”, 

que con sus oraciones siempre me bendijo, lo mismo que a mis hermanos Lety 

“Ortiz” con sus palabras de optimismo; de igual modo les estoy infinitamente 

agradecido a mis hermanos Rubén y Ronald, que desde mi primer día en Europa 

y desde mucho antes siempre me apoyaron. 

Ich danke ganz besonders Frau Verena Meyer-Stumborg, die mich immer 

unterstützt hat; sowie ihrer Familie, bei der ich mich immer willkommen fühlte. 

ii

Short Abstract 

The present work summarizes our research done in the field of 

Polyoxotungstates functionalized by organotin and –antimony linkers. 

After an introduction on iso- and heteropolyoxometalates (generally referred as 

Polyoxometalates, or POMs) and some of their most important applications a 

discussion is devoted to the analytical techniques used in the characterization of 

Polyoxometalates. The next chapters are dedicated to the chemistry of mono- and 

diorganotin functionalized iso- and heteropolytungstates, starting with a more 

specific introduction on the subject, followed by five chapters in which the new 

synthesized compounds are treated in detail, starting from their synthetic 

procedure and characterization in the solid state and in solution (where applies), 

and ending with a discussion of their structural features and conclusion remarks. 

The chapters are organized in terms of the dimensionality of the novel materials 

synthesized, i.e. 3-, 2-, 1-dimensional and discrete molecular assemblies. 

Following the same organization as that used for the chapters devoted to 

organotin functionalized iso- and heteropolyoxometalates; the next one deals 

with organoantimony functionalized POMs; including a discussion on the first 

polyoxotungstate polyanion functionalized with three monophenylantimony 

groups in a sandwich type structure. 

The last chapter deals with two structures without organometallic moieties 

attached to the POM framework, which nevertheless presents very interesting 

structural attributes. Finally, the appendix includes already published as well as 

submitted and accepted material in specialized journals based on the work from 

this manuscript. 

iii

Comprehensive Abstract 

Inorganic metal-oxygen cluster anions, called polyoxometalates (POMs), form a 

class of compounds that is unique in its topological and electronic versatility and 

is of high importance in several disciplines, such as catalysis, medicine and 

material science among others. The functionalization of POMs with 

organometallic moieties covalently attached to the metal-oxo framework 

constitutes an emerging area of interest because the resulting hybrid species 

combine the unique features of both components. 

The present work summarizes our research done in the field of 

polyoxotungstates functionalized by organotin and –antimony linkers as an 

effort to further investigate an area started mainly by Pope and co-workers in the 

United States in the middle 1990´s and later expanded by research groups from 

other parts of the world. 

This manuscript is organized in nine chapters, whereas the first deals with a 

thoroughly introduction on iso- and heteropolyoxometalates, their historical 

background and features, classes of POMs as well as their principal applications. 

Chapter I finish with a summary of the state of the art on organotin and – 

antimony functionalized polyoxoanions depicting briefly what has been done in 

this area so far. 

Chapter II describes the most common analytical techniques used in the 

characterization of POMs, placing special emphasis on the methods and devices 

used to characterize the novel compounds synthesized and depicted in this work, 

finally, the synthetic procedure of the precursors employed throughout our 

investigations is punctually described at the end of this chapter. 

iv

The next chapter describes the general strategy used in our research to 

functionalize polyoxotungstates with organotin and –antimony electrophiles 

taking advantage of the Lewis-acidity of the tin and antimony atoms and the 

hydrolytically stable Sn-C and Sb-C bonds. 

Starting from Chapter IV onwards, a systematic description of all novel 

functionalized compounds is presented. Each chapter is organized in terms of the 

dimensionality of the species, i.e. 3-, 2- and 1-dimension, as well as discrete 

organotin functionalized molecules followed by the organoantimony containing 

polyoxotungstates and finally a chapter devoted to describe a series of novel 

compounds without organometallic moieties attached to the POM framework 

resulted from our investigations. 

In this sense, Chapter IV describes a series of novel 3-dimensional mono- and 

diorganotin functionalized polyoxotungstates where reaction of the (CH 3 ) 2 Sn 2+ 

electrophile toward trilacunary [A-α-XW 9 O 34 ] n- Keggin polytungstates (X = P V , 

As V , Si IV ) with guanidinium as templating-cation resulted in isostructural 

compounds, constituting the first 3-dimensional assemblies of organotinfunctionalized 

polyanions, as well as the first example of a dimethyltincontaining 

tungstosilicate; showing a similar chiral architecture based on 

tetrahedrally-arranged {(CH 3 ) 2 Sn} 3 (A-α-XW 9 O 34 ) monomeric building-blocks 

connected via intermolecular Sn-O=W bridges regardless of the size/charge of 

the heteroatom. A monoethyltin containing polyoxoarsenononatungstate 

presenting exactly the same arrangement in the solid state as those with 

dimethyltin was also obtained. All four species were characterized by singlecrystal 

diffractometry, infrared spectroscopy and thermogravimetry, whereas the 

monoethyltin-containing POM was additionally investigated in solution by 

means of multinuclear magnetic resonance. Unless otherwise, all compounds 

v

described between chapters IV and IX where characterized by the methods just 

mentioned. 

Chapter V describes two isostructural polyanions which represent the first 

examples of diethyltin functionalized polyaoxoarsenates and –phosphates that 

constructs a non-planar 2-D surface in the solid state linked via Sn-O-W bridges 

from only two of the three {Sn(C 2 H 5 ) 2 } 3 groups crafted to the trilacunary [A-α- 

XW 9 O 34 ] n- unit, different to the structures reported in Chapter IV, where all three 

organotin groups participated in the connectivity with other [A-α-XW 9 O 34 ] n- 

building blocks, hence building a 3-dimensional assembly. 

Chapter VI illustrates the most varied kinds of organotin functionalized 

polyoxotungstates as well as the only example of an organotin-containing 

isopolytungstate within this work. The first two species described in this chapter 

are isostructural based on the trivacant [A-β-XW 9 O 33 ] 9- (X = Sb III , As III ) Keggin 

polyanion forming a 1-D chain of dimmers with diethytin groups as linkers. 

Another compound was obtained by interaction of the trilacunary lone-pair 

containing nonatungstoarsenate Keggin polyanion towards diethyltin dichloride 

in aqueous, acidic media at mild temperature conditions resulting in a novel 

diethyltin functionalized polyoxometalates based in the trilacunary (B-β- 

AsW 9 O 33 ) Keggin that forms a one-dimensional chain in the solid state via two 

O-Sn-O(W) bridges. The first functionalized polyoxotungstate with dimethyltin 

electrophiles based on the monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- (P 2 W 20 ) polyanion is 

also described in this chapter, whereas stoichiometric quantities of P 2 W 20 and 

dimethyltindichloride in aqueous, acidic media resulted in 1-D chain of P2W20 

units linked together by means of dimethyltin bridges. Finally, a novel 

isohexatungstate isostructural of the one that Reinoso et al. synthesized with 

dimethyltin (Reinoso, S.; Dickman, M. H.; Kortz, U. Inorg. Chem. 2006, 45, 10422) 

was obtained by reaction of 3 equivalents of sodium tungstate dihydrated with 

vi

one equivalent of diethyltindichloride in aqueous, neutral media. As a result, the 

hexatungstate fragments are linked together via diethyltin moieties. Interestingly, 

both tin atoms are pentacoordinated in a distorted trigonal bipyramidal 

geometry [(C 2 H 5 )SnO 3 ] without water molecules attached to them, whereas the 

ethyl groups are cis to each other. 

A series of discrete molecular assemblies of diethyltin functionalized 

heteropolytungstates are presented in Chapter VIII starting with a novel 

monosubstituted eicosatungstodiphosphate polyanion, which represent the first 

discrete functionalized polyoxotungstate with the diethyltin electrophile based 

on the monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- (P 2 W 20 ) polyanion very similar of that 

described in Chapter VII, but with a monoethyltin moiety incorporated in the 

vacant site of the P 2 W 20 framework instead of two dimethyltin groups. Another 

compound obtained by reaction of stoichiometric amounts of Na 9 [B-α- 

AsW 9 O 33 ]· 27H 2 O and (C 2 H 5 ) 2 SnCl 2 at acidic, aqueous media, resulted in a 

discrete dimmer composed of two (B-β-AsW 9 O 33 ) units linked together via four 

O-Sn-O bridges from four six-coordinated tin atoms (C 2 H 5 ) 2 SnO 4 in a distorted 

octahedral geometry. A mixed-species based on (B-α-AsW 9 O 33 ) resulted from 

reaction of 1 equivalent of K 14 [As 2 W 19 O 67 (H 2 O)] with 3 of (C 2 H 5 ) 2 SnCl 2 in 

aqueous, moderately acidic media, where the polyoxotungstodiarsenate broke in 

two trivacant (B-α-AsW 9 O 33 ) halves giving therefore the appropriate docking 

sites for the diethyltin group to attach; namely two diethyltin groups in one (B-α- 

AsW 9 O 33 ) unit, and the third diethyltin moiety attached on the second 

polyoxoarsenononatungstate. 

The next Chapter, starts with a brief introduction on organoantimony 

functionalized polyoxometalates and follows with the description of a novel 

phenylantimony-containing tungstophosphate, which has a dimeric, sandwichtype 

structure with two (A-α-PW 9 O 34 ) Keggin units capping three octahedral 

vii

{PhSbOH} fragments resulting in an assembly with idealized D 3h symmetry. The 

hydroxo groups all point inside the structure and the phenyl groups away from 

it. 

Finally, Chapter IX deals with two novel structures which do not contain any 

organometallic moiety bonded to the POM framework. Such species where 

obtained as a result of countless experiments made throughout almost three 

years of our research yet we decided to include them at the end of this 

manuscript due to their novelty. First, the chiral sandwich-type polyanion based 

on two (A-α-PW 9 O 34 ) units with three antimony (III) in between is described, 

analogue of that discovered by Pope et al. in 1996 with Sn II (Xin, F.; Pope, M. T. J. 

Am. Chem. Soc. 1996, 118, 7731). Second, a plenary polyoxodiselenotungstate is 

illustrated and obtained in aqueous, very acidic media from sodium tungstate, 

selenous acid and diethyltin dichloride, even when the latter does not participate 

in the final product. 

viii

Index 

Acknowledgments 

Short Abstract 

Comprehensive Abstract 

List of Figures/Schemes 

List of Tables 

List of Structures with Codes 

i 

iii 

iv 

xix 

xxvi 

xxviii 

Chapter I. Iso- and Heteropolyoxometalates. An Introduction 

1.1 Historical Background 2 

1.2 General Description of Polyoxometalates (POMs) 4 

1.2.1 The Anderson-Evans Isopoly- and Heteropolyanions 

[M 7 O 24 ] n- , [XM 6 O 24 ] m- 7 

1.2.2 The Lindqvist Isopolyhexametalate [M 6 O 19 ] n- 8 

1.2.3 The Keggin Heteropolyanion [XM 12 O 42 ] n- , 

Isomeric forms and vacant derivatives 9 

1.2.3.1 Redox Properties of the Keggin heteropolyanion 11 

1.2.3.2 Isomeric Forms of the Keggin Heteropolyanion: 

Baker Figgis Isomers 12 

1.2.3.3 Lacunary Species of the Keggin Heteropolyanion 14 

1.2.3.4 Lacunary Species derived from the 

[α-XM 12 O 40 ] n- isomer 14 


[β-XM 12 O 40 ] n- isomer 15 


[γ-XM 12 O 40 ] n- isomer 16 

ix

1.2.4 The Wells-Dawson [X 2 W 18 O 62 ] 6- (X = P V , As V ) 

Heteropolyanions and its lacunary species from the α isomer 18 


[α-X 2 W 18 O 62 ] 6- isomer 19 

1.2.5 The Henicosatungstodiphosphate and –arsenate 

[X 2 W 21 O 71 (H 2 O) 3 ] 6- (X = P V , As III ) polyanion and 

their mono- und dilacunary derivatives 20 

1.2.5.1 The monolacunary [P 2 W 20 O 70 (H 2 O) 2 ] 10- polyanion 21 

1.2.5.2 The dilacunary [X 2 W 19 O 69 (H 2 O)] n- (X = P V , As III ) 

polyanion 23 

1.3 Applications 24 

1.3.1 Catalysis 24 

1.3.2 Medicine 25 

1.3.3 Hybrid Organic-Inorganic Materials 26 

1.4 State of the Art on Organotin and –antimony Functionalized 

Polyoxoanions 27 

1.4.1 Monoorganotin Functionalized Polyoxometalates 27 

1.4.1.1 Knoth´s Work 27 

1.4.1.2 Pope´s Work 28 

1.4.1.3 Hasenknopf´s Work 31 

1.4.1.4 Liu´s Work 32 

1.4.1.5 Krebs´ Work 33 

1.4.2 Diorganotin Functionalized Polyoxometalates 34 

1.4.2.1 Kortz´s Work 34 

1.4.3 Organoantimony Functionalized Polyoxometalates 40 

1.5 References 41 

x

Chapter II. Analytical Techniques used in the Characterization of 

POMs and Synthesis of Precursors. 

2.1 Infrared Spectroscopy 54 

2.2 Thermogravimetry 54 

2.3 Single Crystal X-ray Diffraction 55 

2.4 Elemental Analysis 56 

2.5 Nuclear Magnetic Resonance (NMR) Spectroscopy 57 

2.5.1 17 O NMR of Polyoxometalates 57 

2.5.2 183 W NMR of Polyoxometalates 57 

2.5.2.1 183 W NMR of the Keggin Structure and 

their Derivatives 58 

2.5.2.2 183 W NMR of the monovacant 

Eicosatungstodiphosphate [P 2 W 20 O 70 (H 2 O) 3 ] 10- 61 

2.6 Synthesis of Precursors 63 

2.6.1 Synthesis of Trilacunary Keggin Polyanions 63 

2.6.1.1 Na 9 [B-α-SbW 9 O 33 ] · 27H 2 O 63 

2.6.1.2 Na 9 [B-α-AsW 9 O 33 ] · 27H 2 O 64 

2.6.1.3 Na 9 [A-α-AsW 9 O 34 ] · 18H 2 O 64 

2.6.1.4 Na 9 [A-α-HSiW 9 O 34 ] · 23H 2 O 64 

2.6.1.5 Na 9 [A-α-HGeW 9 O 34 ] · 23H 2 O 64 

2.6.1.6 Na 9 [A-α-PW 9 O 34 ] · 7H 2 O 65 

2.6.1.7 Na 9 [B-α-BiW 9 O 33 ] · 16H 2 O 65 

2.6.2 Synthesis of Dilacunary Keggin Polyanions 65 

2.6.2.1 Cs 7 [γ-PW 10 O 36 ] · H 2 O 65 

xi

2.6.2.2 K 8 [γ-SiW 10 O 36 ] · 20H 2 O 66 

2.6.2.3 K 8 [γ-GeW 10 O 36 ] · 6H 2 O 66 

2.6.3 Synthesis of Monolacunary Keggin Polyanions 67 

2.6.3.1 K 8 [α-SiW 11 O 39 ] · 13H 2 O 67 

2.6.3.2 K 8 [β 2 -GeW 11 O 39 ] · 14H 2 O 67 

2.6.3.3 K 7 [α-PW 11 O 39 ] · 14H 2 O 68 

2.6.4 Synthesis of Mono- Di- and Hexavacant 

Wells-Dawson Polyanions 68 

2.6.4.1 K 10 [α 2 -P 2 W 17 O 61 ] · 20H 2 O 68 

2.6.4.2 Na 12 [α-P 2 W 15 O 56 ] · 24H 2 O 68 

2.6.4.3 K 12 [α-H 2 P 2 W 12 O 48 ] · 24H 2 O 69 

2.6.5 Synthesis of further Polyoxotungstophosphate Species: The 

Monovacant Eicosatungstodiphosphate, Divacant 

Nonadecatungstodiphospate and Octatetracontatungstooctaphosphate 

Polyanions 70 

2.6.5.1 K 14 [P 2 W 19 O 69 (H 2 O)] · xH 2 O 70 

2.6.5.2 K 10 [P 2 W 20 O 69 K(H 2 O) 2 ] · 24H 2 O 70 

2.6.5.3 K 28 Li 5 H 7 [P 8 W 48 O 184 ] · 92H 2 O 71 

2.6.6 Synthesis of further Polyoxotungstoarsenate Species: The 

Monovacant Eicosatungstodiarsenate and the 

Tetracontatungstotetraarsenate (III) Polyanions 71 

2.6.6.1 K 14 [As 2 W 19 O 67 (H 2 O)] · xH 2 O 71 

2.6.6.2 Na 27 [NaAs 4 W 40 O 140 ] · 60H 2 O 72 

2.7. References 73 

xii

Chapter III. General Introduction on Mono- and Diorganotin 

Functionalized Iso- and Heteropolytungstates 

3.1 Introduction 77 

3.2 General Experimental Procedure for the Functionalization of Polyoxotungstates with 

Organotin Groups 79 

3.3 General Characterization Procedure for Polyoxotungstates 

Functionalized with Organotin Groups 83 


Chapter IV. 3-D Assemblies of Mono- and Diorganotin 

Functionalized Heteropolytungstates 

4.1 3-D Assemblies of Dimethyltin Functionalized [A-α-XW 9 O 34 ] n- (X = P V , As V , Si IV ) 

Keggin polytungstates 89 

4.1.1 Synthetic Procedure 90 

4.1.2 FT-Infrared Spectroscopy 91 

4.1.3 Thermogravimetry 93 

4.1.4 Single Crystal X-ray Diffraction 95 

4.2 3-D Assembly of an Ethyltin Functionalized [A-α-AsW 9 O 34 ] 9- Keggin 

polyoxotungstate 100 




xiii


4.2.5 Solution Studies (Nuclear Magnetic Resonance) 109 

4.3 Conclusions 113 


Chapter V. 2-D Assemblies of Diethyltin Functionalized 

Heteropolytungstates 

5.1 2-D Assemblies of Diethyltin Functionalized [A-α-XW 9 O 34 ] n- 

(X = P V , As V ) Keggin Polytungstates 115 





5.1.5 Conclusions 125 


xiv

Chapter VI. 1-D Assemblies of Diorganotin Functionalized Heteroand 

Isopolytungstates 

6.1 The [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-XW 9 O 33 ) 2 ] 6- (X = Sb III , As III ) Lone-Pair 

Polyoxotungstate Dimer and its 1-D Architecture in the Solid State 127 





6.2 A Lone-Pair Tungstoarsenate [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )] 3- and its 

1-Dimensional Arrangement through Diethyltin Bridges 138 





6.3 The Dimethyltin Functionalized Eicosatungstodiphosphate Polyanion: 

[{Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 K(H 2 O) 2 )] 5- 146 





6.4 The Diethyltin Functionalized Hexatungstate Isopolyanion: 

[{Sn(C 2 H 3 ) 2 } 2 (W 6 O 22 )] 4- 153 





xv



Chapter VII. Discrete Molecular Assemblies of Diethyltin 


7.1 The Diethyltin Functionalized Eicosatungstodiphosphate Polyanion: 

[{Sn(C 2 H 5 ) 2 (H 2 O) 2 }(P 2 W 20 O 70 K(H 2 O) 2 )] 7- 164 





7.2 A Novel Diethyltin Functionalized Dimer Based on the Lone-Pair Containing 

Trivacant Nonatungstoarsenate Keggin Anion: 

[{Sn(C 2 H 5 ) 2 (H 2 O)} 3 (B-β-AsW 9 O 33 )] 6- 2 172 





7.3 The Keggin-based Mixed Species [{Sn(C 2 H 5 ) 2 (H 2 O)}(B-α-AsW 9 O 33 )- 

{Sn(C 2 H 5 ) 2 (H 2 O)} 2 (B-α-AsW 9 O 33 )] 12- 

Diethyltin Containing Polyanion 180 




xvi




Chapter VIII. The Novel Phenylantimony Containing 

Polyoxotungstate: [{PhSbOH}3(A-α-PW9O34)2] 9- 

8.1 General Introduction on Organoantimony Functionalized Polyoxometalates 191 

8.2 Organoantimony-Containing Polyoxometalate: 

[{PhSbOH} 3 (A-α-PW 9 O 34 ) 2 ] 9- 193 





8.2.5 Solution Studies (Nuclear Magnetic Resonance) 200 

8.2.6 Conclusions 203 


xvii

Chapter IX. Structures without Organometallic Moieties attached to 

the POM Framework 

9.1 The Chiral Sandwich-Type [Sb 3 

III (A-α-PW 9 O 34 ) 2 ] 9- 

Lone-Pair containing Polyanion 207 





9.2 A Novel [H 3 Se 2 W 22 O 74 (H 2 O) 7 ] 5- Plenary Polyoxodiselenotungstate 215 






Appendix 

A. Published Articles 

B. Submitted and Accepted Articles (stand: June 2009) 

C. Compact Disc with crystallographic information (cif files) of structures 1 to 17 

xviii

List of Figures/Schemes 

Figure 1.1 The Anderson-Evans heptamolybdate anion [Mo 7 O 24 ] 6- 7 

Figure 1.2 The Lindqvist hexatungstate anion [W 6 O 19 ] 2- 9 

Figure 1.3 The [XM 12 O 42 ] n- Keggin structure in polyhedral representation: four 

corner shared {M 3 O 13 } triads (depicted in different colours) wrapping the central 

[XO 4 ] tetrahedron 10 

Figure 1.4 The five Baker-Figgis isomers of the Keggin polyanion 13 

Figure 1.5 The mono- and trilacunary species derived from the [α-XM 12 O 40 ] n- 

Keggin heteropolyanion 14 

Figure 1.6 The three monolacunary species derived from the [β-XM 12 O 40 ] n- 

Keggin heteropolyanion 15 

Figure 1.7 Trilacunary species derived from the [β-XM 12 O 40 ] n- Keggin 

heteropolyanion 16 

Figure 1.8 [γ-XM 10 O 36 ] m- . The only lacunary specie derived from the 

[γ-XM 12 O 40 ] n- Keggin heteropolyanion 17 

Figure 1.9 The Wells-Dawson [α-X 2 W 18 O 62 ] 6- (X = P V , As V ) 

heteropolyanion 18 

Figure 1.10 Monolacunary species of the Wells-Dawson polyanion 

(a) [α 1 -X 2 W 17 O 61 ] 10- , (b) [α 2 -X 2 W 17 O 61 ] 10- 19 

Figure 1.11 Tri- and Hexalacunary species of the Wells-Dawson polyanion 

(a) [P 2 W 15 O 56 ] 12- , (b) [H 2 P 2 W 12 O 48 ] 12- 20 

xix

Figure 1.12 [X 2 W 21 O 71 (H 2 O) 3 ] n- , (a) X = P V , (b) X = As III 21 

Figure 1.13 The monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- polyanion with a potassium 

cation in the cavity. (a) Front view, (b) Side view 22 

Figure 1.14 The divacant [As 2 W 19 O 69 (H 2 O)] 14- polyanion with four potassium 

cations in the cavity. (a) Front view, (b) Side view 23 

Figure 1.15 The sandwich type [(BuSnOH) 3 (α-SiW 9 O 34 ) 2 ] 14- polyanion 28 

Figure 1.16 The sandwich type [(PhSn) 3 Na 3 (α-SbW 9 O 33 ) 2 ] 6- polyanion 29 

Figure 1.17 [(n-C 4 H 9 Sn) 2 Zn 2 (B-α-PW 9 O 34 ) 2 ] 8- 31 

Figure 1.18 The dodecameric [{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 ) polyanion 35 

Figure 1.19 The [{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ] 28- polyanion 36 

Figure 1.20 The [{(CH 3 ) 2 Sn} 6 (OH) 2 O 2 (H 2 BW 13 O 46 ) 2 ] 12- polyanion 38 

Figure 1.21 The flower pot [{(C 6 H 5 )Sn(OH)} 3 (A-α-GeW 9 O 34 )] 4- polyanion 39 

Figure 2.1 Polyhedral representation of the [XW 12 O 40 ] (8−n)− Keggin anion 59 

Figure 2.2 Front view of the monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- (P 2 W 20 ) polyanion 

with a potassium cation in the cavity 62 

Figure 3.1 Polymeric Structure of Me 2 SnCl 2 and Et 2 SnCl 2 in the solid state 79 

Figure 4.1 FT-Infrared Spectra of compounds GNa-1 (red), GNa-2 (blue) 

and GNa-3 (green) 92 

Figure 4.2 Thermogram of compound GNa-1 93 



xx

Figure 4.5 Combined polyhedral/ball-and-stick representation of the 

{(CH 3 ) 2 Sn} 3 (A-α-XW 9 O 34 ) monomeric building-block in 1 – 3 96 

Figure 4.6 Guanidinium templated tetrahedral arrangement of 

monomers in the unit cell 97 

Figure 4.7 Detail of the connectivity of a {(CH 3 ) 2 Sn} 3 (A-α-XW 9 O 34 ) monomeric 

building block (centre) with monomers from adjacent unit cells 98 

Figure 4.8 FT-Infrared Spectrum of compound G-4 101 

Figure 4.9 Thermogram of compound G-4 102 


{Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 )]monomeric building-block in 4 103 

Figure 4.11 Guanidinium templated tetrahedral arrangement of monomers in the 

unit cell 106 

Figure 4.12 Connectivity of a {Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 ) monomeric 

building block (center) with monomers from adjacent unit cells 107 

Figure 4.13 1 H NMR spectrum of 4 from the fresh reaction mixture in H 2 O/D 2 O 

media at room temperature 109 

Figure 4.14 13 C NMR spectrum of 4 from the fresh reaction mixture in H 2 O/D 2 O 

media at room temperature 110 

Figure 4.15 119 Sn NMR spectrum of 4 from the fresh reaction mixture in 

H 2 O/D 2 O media at room temperature 111 

Figure 4.16 183 W NMR spectrum of 4 from the fresh reaction mixture in 

H 2 O/D 2 O media at room temperature 112 

xxi






[{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α- XW 9 O 34 )] 3- monomeric building-block in 5 and 6 121 

Figure 5.6 Combined polyhedral/ball-and-stick representation of the 2-D solidstate 

structure of [C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-XW 9 O 34 )]· nH 2 O [X = As V (5), 

P V (6)] 123 





Figure 6.5 Combined polyhedral/ball-and-stick representation of 

[{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-XW 9 O 33 ) 2 ] (X = Sb III , As III ) Dimmer 133 

Figure 6.6 Combined Polyhedral/ball-and-stick representation of the 1-D chain 

composed of [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-XW 9 O 33 ) 2 ] (X = Sb III , As III ) Dimmers 134 




[{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )]monomeric building-block in 9 141 

xxii


1-dimensional arrangement of 9 composed of [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )] 

building-blocks 144 



Figure 6.13 Combined polyhedral and ball-and-stick representation of a 

{Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 K(H 2 O) 2 ) 5- unit of polyanion 10. Front side (left) and 

upper side (right) 150 

Figure 6.14 Combined polyhedral and ball-and-stick representation of a 1-D 

chain composed of {Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 (H 2 O) 2 K) 5- units 151 



Figure 6.17 Combined polyhedral /ball-and-stick representation of the polymeric 

[{Sn(C 2 H 5 ) 2 } 2 (W 6 O 22 )] 4- building block 156 


1-dimensional chain composed of [{Sn(C 2 H 5 ) 2 } 2 (W 6 O 22 )] 4- building blocks 158 



Figure 7.3 Combined polyhedral and ball-and-stick representation of 12 (left: 

front view with atom labeling, right: upper view) 168 



xxiii


[{Sn(C 2 H 5 ) 2 (H 2 O)} 3 (B-β-AsW 9 O 33 )] 6- 2 176 


[{Sn(C 2 H 5 ) 2 (H 2 O)} 3 (B-β-AsW 9 O 33 )] 6- 2 in a side view (left) and 

upper view (right) 177 




[{Sn(C 2 H 5 ) 2 (H 2 O)}(B-α-AsW 9 O 33 ){Sn(C 2 H 5 ) 2 (H 2 O)} 2 (B-α-AsW 9 O 33 )] 12- 184 

Figure 8.1 Ball-and-stick representation of 

(n-Bu 4 N) 2 [(Ph 2 Sb) 2 (μ-O) 2 (μ-WO 4 )] 2 192 

Figure 8.2 Combined polyhedral / ball-and-stick representation of 

[Mn(PhSb) 12 O 28 {Mn(H 2 O) 3 } 2 {Mn(H 2 O) 2( AcOH)} 2 ] 193 

Figure 8.3 FT-Infrared Spectrum of compound Cs-15 195 

Figure 8.4 Thermogram of compound Cs-15 196 

Figure 8.5 Combined polyhedral/ball-and-stick representation of 15 197 

Figure 8.6 183 W NMR spectrum of 15 in H 2 O/D 2 O media 200 

Figure 8.7 31 P NMR spectrum of 15 in H 2 O/D 2 O media 201 

Figure 8.8 13 C NMR (left) and 1 H (right) spectra of 15 in H 2 O/D 2 O media 202 

Figure 9.1 FT-Infrared Spectra of compounds PMNa-16 (blue) and the 

Na 9 [A-α-PW 9 O 34 ]· 7H 2 O precursor (red) 210 

Figure 9.2 Thermogram of compound PMNa-16 211 

xxiv

Figure 9.3 Combined polyhedral/ball-and-stick representation of 16 212 

Figure 9.4 FT-Infrared Spectrum of compound Cs-17 217 

Figure 9.5 Combined polyhedral and ball-and-stick representation of 17. a) front 

view, b) side view 218 

Scheme 1.1 Preparation of Functionalized Wells-Dawson 

Polyoxotungstates 32 

Scheme 3.1 Hydrolytic Sequence of Diorganotindichloride Species 81 

xxv

List of Tables 

Table 1.1 Diversity of Polyoxometalates with some examples 6 

Table 1.2 Heteropolytungstates with the Anderson-Evans structure 7 

Table 1.3 Heteropolymolybdates with the Anderson-Evans structure 8 

Table 4.1 Selected Bond Lengths (Å) and Angles (°) 

of Polyanions 1, 2 and 3 96 

Table 4.2 Crystallographic Data for Compounds 

GNa-1, GNa-2 and GNa-3 99 

Table 4.3 Selected Bond Lengths (Å) and Angles (°) of Polyanion 4 104 

Table 4.4 Crystallographic Data of Compound G-4 108 


of Polyanions 5 and 6 122 

Table 5.2 Crystallographic Data of Compounds G-5 and G-6 124 



Table 6.2 Crystallographic Data of Compounds G-7 and G-8 137 




xxvi

Table 6.6 Selected Bond Lengths (Å) and Angles (°) of polyanion 11 and 

[{(CH 3 ) 2 Sn} 2 (W 6 O 22 )] 4- 157 










Table 8.2 Crystallographic Data of Compound Cs-15 199 

Table 8.3 Comparison of 183 W NMR Chemical Shifts for 15 and Structurally 

Related Phenyltin Derivatives 201 

Table 9.1 Selected Bond Lengths (Å) and Angles (°) of Polyanions 16 and 

[Sn II 3(A-α-PW 9 O 34 ) 2 ] 12- 213 

Table 9.2 Crystallographic Data of Compound PMNa-16 214 

Table 9.3 Crystallographic Data of Compound Cs-17 219 

xxvii

List of Structures with Codes 

([C(NH 2 ) 3 ] 2 Na[{(CH 3 ) 2 Sn(H 2 O)} 3 (A-α-AsW 9 O 34 )]· 8H 2 O) ∞ 

([C(NH 2 ) 3 ] 2 Na[{(CH 3 ) 2 Sn(H 2 O)} 3 (A-α-PW 9 O 34 )]· 9H 2 O) ∞ 

([C(NH 2 ) 3 ] 2 Na[{(CH 3 ) 2 Sn(H 2 O)} 3 (A-α-SiW 9 O 34 )]· 10H 2 O) ∞ 

([C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 )]· 5H 2 O) ∞ 

([C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-AsW 9 O 34 )]· 9H 2 O) ∞ 

([C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-PW 9 O 34 )]· 2H 2 O) ∞ 

([C(NH 2 ) 3 ] 6 [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-SbW 9 O 33 ) 2 ]· 7H 2 O) ∞ 

([C(NH 2 ) 3 ] 6 [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-AsW 9 O 33 ) 2 ]· 8H 2 O) ∞ 

([C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )]· H 2 O) ∞ 

([C(NH 2 ) 3 ] 5 [{Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 K(H 2 O) 2 )] · 18H 2 O) ∞ 

([C(NH 2 ) 3 ] 4 [{Sn(C 2 H 5 ) 2 } 2 (W 6 O 22 )]·5H 2 O) ∞ 

[C(NH 2 ) 3 ] 7 [{Sn(C 2 H 5 ) 2 (H 2 O) 2 }P 2 W 20 O 70 K(H 2 O) 2 ]·13H 2 O 

[C(NH 2 ) 3 ] 6 [{Sn(C 2 H 5 ) 2 (H 2 O)} 3 (B-β-AsW 9 O 33 )] 2 ·5H 2 O 

(GNa-1) 

(GNa-2) 

(GNa-3) 

(G-4) 

(G-5) 

(G-6) 

(G-7) 

(G-8) 

(G-9) 

(G-10) 

(G-11) 

(G-12) 

(G-13) 

[C(NH 2 ) 3 ] 12 [{Sn(C 2 H 5 ) 2 (H 2 O)}(B-α-AsW 9 O 33 ){Sn(C 2 H 5 ) 2 (H 2 O)} 2 (B-α-AsW 9 O 33 )]·7H 2 O 

(G-14) 

Cs 9 [{PhSbOH} 3 (A-α-PW 9 O 34 ) 2 ]· 24H 2 O 

[PhMe 3 N]Na 8 [Sb 3 

III (A-α-PW 9 O 34 ) 2 ] · 17H 2 O 

Cs 5 [H 3 Se 2 W 22 O 74 (H 2 O) 7 ] · nH 2 O 

(Cs-15) 

(PMNa-16) 

(Cs-17) 

xxviii


Chapter I. Iso- and Heteropolyoxometalates. 

An Introduction 

Inorganic metal-oxygen cluster anions form a class of compounds that is 

unique in its topological and electronic versatility and is of high importance in 

several disciplines. Scientists such as Berzelius, Werner, and Pauling appear in 

the early literature of the field. These clusters (so-called isopoly- and 

heteropolyanions) contain highly symmetrical core assemblies of MO x 

, units 

(M = V, Mo, W) and often adopt quasi-spherical structures based on 

Archimedean and Platonic solids of considerable topological interest. 

Understanding the driving force for the formation of high-nuclearity clusters 

is still a formidable challenge. Polyoxoanions are important models for 

elucidating the biological and catalytic action of metal-chalcogenide clusters, 

since metal-metal interactions in the oxo clusters range from very weak 

(virtually none) to strong (metal-metal bonding) and can be controlled by 

choice of metal (3d, 4d, 5d), electron population (degree of reduction), and 

extent of protonation. 1c 

Polyoxometalates (POMs) have found applications in analytical and clinical 

chemistry, catalysis (including photocatalysis), biochemistry (electron 

transport inhibition), medicine (antitumoral, antiviral, and even anti-HIV 

activity), and solid-state devices. These fields are the focus of much current 

research. Metal-oxygen clusters are also present in the geosphere and possibly 

in the biosphere. 

1


1.1 Historical Background 

In 1826 Berzelius prepared from the mixture of ammonium molybdate and 

phosphoric acid, what is now known as the first POM, a yellow precipitate 

which now is known as ammonium 12-molybdophosphonate: 

(NH 4 ) 3 [PMoO 40 ]. 2 A few years later, Struve reported the heteropoly 

molybdates of Cr 3+ and Fe 3+ (the term heteropoly is referred to POMs with 

oxygen, molybdenum in this particular case, and another atom i.e. the 

heteroatom: chromium or iron) . 3 Nevertheless, the discovery of the 

tungstosilicilic acids and their salts by Marignac in 1862 allowed the precise 

analytical composition of such compounds. 4a,b 

Rosenheim and Jaenicke 5 published a review in 1917 describing several 

dozens of new heteropoly acids and even a greater number of salts derived of 

those compounds. By this time, the amount of synthesized polyanions was 

fairly numerous and the first attempts to understand their composition were 

based on Werner´s coordination theory. Miolati and Pizzighelli 6 developed a 

theory which was afterwards adopted by Rosenheim, who was probably the 

most influential scientist in the field of polyanion chemistry in the first three 

decades of the twentieth century. 

In 1929, Linus Pauling suggested a cage structure of MoO 6 octahedra joined 

by corners into a shell enveloping the PO 3- 4 ion, opposite to the Miolati- 

Rosenheim theory which suggested that heteropoly acids were based on sixcoordinate 

heteroatoms with MO 2- 4 or M 2 O 2- 7 anions as ligand or bridging 

groups. 7 

The first definitive information on a heteropoly compound was provided by 

Keggin in 1933 by means of X-ray diffraction proving that the WO 6 octahedral 

units in H 3 [PW 12 O 40 ]· 5H 2 O were in fact connected by both shared edges and 

corners. 8 The 12-tungstophosphoric acid was studied in the following years by 

2


single-crystal X-ray and neutron diffraction disclosing that in fact 6 water 

molecules and not five are present. In 1977 Brown et al. 9 confirmed the 

structures based on H 3 [PW 12 O 40 ]· nH 2 O finding not five but six waters of 

hydration as well as other two hydrates, namely n = 21 10 , 29. 11 

After the work done on the 12-tungstophosphoric acid, a number of 

isomorphous complexes appeared; nevertheless it was not until 1948 when 

Evans 12 reported a new heteropolyanion structure based on Te and Mo in a 

1:6 ratio, namely the [TeMo 6 O 24 ] 6- polyanion, whose structure had been 

suggested by Anderson twelve years earlier. In 1950, Lindqvist 13 reported the 

novel heptamolybdate [Mo 7 O 24 ] 6- anion. A few years later, in 1953, Dawson 14 

reported another structure closely related to the Keggin, now known as the 

Wells-Dawson structure: [P 2 W 18 O 62 ] 6- . By the first half of the twentieth 

century, the Keggin, Anderson-Evans, Lindqvist and Wells-Dawson 

structures served as a platform for the discovery of dozens of new other 

compounds in decades to come plus many others unknown at that time. 

By the 1970´s, the POM chemistry expanded greatly due to the development 

of analytical techniques and their inclusion to laboratories, such as single X- 

ray diffraction, infrared and Raman spectroscopy as well as multinuclear 

NMR. Precisely this last technique allowed studying polyanions in solution, 

permitting to expand the knowledge on the structural features of POMs 

beyond the solid state. This decade is associated with widespread work of 

several groups around the world, worth to mention those of Jahr (Germany), 

Sillén (Sweden), Souchay (France), Ripan (Rumania), Spitsyn (former USSR) 

and Baker (USA). 

During the last 20 years of the twentieth century, the number of groups 

dedicated to the investigation of polyanions increased considerably. The 

monograph of Pope 1 delivers an update in POM chemistry up to 1983. A more 

concise review of Pope and Müller 15 appeared in 1991. In 1998, Baker and 

3


Glick 16 published a very complete historical perspective of this field. By 1995, 

the single X-ray crystal structures for approximately 180 POMs had been 

reported. 17 By the end of the twentieth century, the largest POM ever 

synthesized consisted of a giant wheel-shaped polyoxomolybdate, 4 

nanometres in diameter, made up of 154 molybdenum atoms embedded in a 

network of oxygen atoms. 18 

POM chemistry has experienced an unprecedented development in terms not 

only in size of recently synthesized polyanions, but also the continuous 

advance in analytical techniques permit a deeper understand of the structural 

features that impact the continuous growing applications of such molecules. 

1.2 General Description of Polyoxometalates (POMs) 

In its broader definition, POMs can be considered as Isopolyanions of general 

formulae [M m O y ] p- (M = Mo, W, V, Nb, Ta) and Heteropolyanions: [X x M m O y ] q- 

(x ≤ m and X, which is defined as the heteroatom). Whereas M is commonly 

tungsten or molybdenum, or a combination of these two; less frequently the 

other mentioned elements since a number of strict conditions need to be 

satisfied, i.e. a favourable combination of ionic radius and charge, as well as 

the ability to form dπ-pπ M-O bonds. Fewer restrictions are there in terms which 

element can be the heteroatom, and up to date more than 70 elements from all 

groups of the periodic table have been encountered in POMs (except the noble 

gases). It is worth to mention at this point, that the terms polyanion and 

polyoxometalate (POM) will be used interchangeably. 

The structures of POMs are described in terms of assemblies of metal-centered 

MO n polyhedra that are linked by shared corners, edges, and less common 

faces. Lipscomb 19 noted that no heteropoly- or isopolyanion structure 

contained addenda MO 6 octahedra with more than two unshared atoms, 

4


suggesting that this might be a general feature of all polyanion structures. 

Structures that appear to contradict the Lipscomb principle are uncommon 

and may be rationalized either by protonation of a fac MO 3 group to cis 

MO 2 (OH), as in the case of a novel (W 6 O 22 ) 8- isopolytungstate synthesized by 

Reinoso et al. in 2006. 20 This (W 6 O 22 ) 8- unit forms a 1-D polymer in the solid 

state by means of (CH 3 ) 2 Sn 2+ bridges, however, close inspection of the 

(W 6 O 22 ) 8- fragment reveals that each of the three pairs of tungsten centres 

exhibits a different number of terminal bonds. Thus, this hexatungstate 

violates the Lipscomb rule. 

Another important feature concerning the metal displacement observed in 

polyanions were found by Pope, 1a namely: metal atom displacement towards 

one terminal oxygen atom (Type I); and metal atom displacement towards two 

cis commonly terminal oxygen atoms (Type II). 

The huge variety of POMs compositions and structures is determined by the 

ability of such complexes to include heteroatoms. A further way to classify 

POMs in terms not only of the presence of a heteroatom but also the incidence 

of mixed addenda atoms, organic groups attached to the polyanion, 

polymeric species, etc. is illustrated in table 1.1. 

5


Table 1.1. Diversity of POMs with some examples. 21 

Isopolyanions [V 4 O 12 ] 4- , [Ta 6 O 19 ] 8- , [Mo 7 O 24 ] 6- , [W 10 O 32 ] 4- 

Heteropolyanions [PW 12 O 40 ] 3- , [P 2 W 18 O 62 ] 6- , [PV 14 O 42 ] 9- , [MnMo 9 O 32 ] 6- 

Isopoly- and 

heteropolyanions 

with mixed 

addenda atoms 

Functionalized 

POMs 

Organometallic 

and alkoxo 

derivatives 

Cryptand/Clathrate 

POMs 

Polymeric species 

[Nb 2 W 4 O 19 ] 4- , [PV 2 Mo 10 O 40 ] 5- 

[PW 11 O 39 RhCH 2 COOH] 5- , [{PhSbOH} 3 (A-α-PW 9 O 34 ) 2 ] 9- 

[PW 12 O 39 (OMe)] 2- , [V 6 O 13 {(OCH 2 ) 3 (CNO 2 )} 2 ] 2- 

[│Na(H 2 O)│P 5 W 30 O 110 ] 14- , [│Cl│V 18 O 42 H 4 ] 9- 

{[{(CH 3 ) 2 Sn} 2 (W 6 O 22 )] 4- } ∞ , {[V 5 O 14 ] 3- } ∞ 

It is important to insist that Table 1.1 illustrates only a small portion of the 

variety of polyanions that have been synthesized and characterized up to date, 

nonetheless the broad nomenclature Isopoly- and heteropolyanion gave by Pope 

is the adequate one independent of the nature of other atoms, organic groups 

or derivatives that may be present in the polyanion. 

The following paragraphs are devoted to explore briefly the structural 

features of the Anderson-Evans, Lindqvist, Keggin, Wells-Dawson as well as 

a class of heteropolytungstophosphate and -arsenate species; since most of the 

structures reported in this work are based on the latter and Keggin species, 

special attention will be dedicated to these polyanions. If not described 

otherwise, polyhedral representation of polyanions will be used through this 

work. The octahedral nature of the MO 6 building block of all polyanions 

permits a more easy understanding of the structural features of such 

compounds. 

6


1.2.1 The Anderson-Evans Isopoly- and Heteropolyanions [M7O24] n- , 

[XM6O24] m- 

Two polyanion structures are based on the arrangements of seven edgeshared 

octahedra (Figure 1.1), whereas the planar structure was originally 

proposed by Anderson for the heptamolybdate anion [Mo 7 O 24 ] 6- . 

Figure 1.1 The Anderson-Evans 

heptamolybdate anion [Mo 7 O 24 ] 6- . 

The Anderson-Evans structure has a D 3d symmetry and a vast number of 

transition metals in oxidation states that range fro +2 to +7 have been found to 

occupy the position of the heteroatom, 1 

examples of Anderson-Evans structures. 

Tables 1.2 and 1.3 illustrates some 

Table 1.2. Heteropolytungstates with the Anderson-Evans structure. 

Heteroatom Example Reference 

Pt IV [H 3 PtW 6 O 24 ] 5- 22 

Mn IV [MnW 6 O 24 ] 8- 23 

Sb V [SbW 6 O 24 ] 7- 24 

Te VI [TeW 6 O 24 ] 6 - 25 

Ni II [H 6 NiW 6 O 24 ] 2- 26 

7


Table 1.3. Heteropolymolybdates with the Anderson-Evans structure. 

Heteroatom Example Reference 

Zn II [H 6 ZnMo 6 O 24 ] 4- 27 

Cu II [H 6 CuMo 6 O 24 ] 4- 28 

Ni II [H 6 NiMo 6 O 24 ] 4- 29 

PtI V [H 6 PtMo 6 O 24 ] 2- 30 

Co III [H 6 CoMo 6 O 24 ] 3- 31 

Rh III [H 6 RhMo 6 O 24 ] 3- 32 

Cr III [H 6 CrMo 6 O 24 ] 3- 33 

Al III [H 6 AlMo 6 O 24 ] 3- 34 

Ga III [H 6 GaMo 6 O 24 ] 3- 35 

Te VI [TeMo 6 O 24 ] 6 - 36 

I VII [IMo 6 O 24 ] 5- 37 

The Anderson-Evans structure allows the central Mo VI and W VI atoms to 

adopt a type II (cis-dioxo) environment like the remaining addenda. 

1.2.2 The Lindqvist Isopolyhexametalate [M 6 O 19 ] n- 

The Lindqvist isopolyanion has an average O h symmetry (Figure 1.2) and 

only a few species exist, basically with Nb V , V V , Ta V , Mo VI and W VI i.e. 

[Mo 6 O 19 ] 2- 38 , [W 6 O 19 ] 2- 39 , [Ta 6 O 19 ] 8- 40 , [V 6 O 19 ] 8- . 41 

Some other complexes with the [M 6 O 19 ] n- structure include mixed 

isopolyanions such as the vanadium-tungsten (2:4) and niobium-tungsten 

(3:3) 1 structures. 

8


Figure 1.2 The Lindqvist 

hexatungstate anion [W 6 O 19 ] 2- . 

1.2.3 The Keggin Heteropolyanion [XM12O40] n- , Isomeric forms and 

vacant derivatives 

Condensation of [MO 6 ] octahedra in presence of tetrahedral heterooxoanions 

[XO 4 ] results in a large number of heteropolyanions whose structures are 

based on the [XM 12 O 40 ] n- Keggin structure. 8a This structure has an overall T d 

symmetry and is based on a central [XO 4 ] tetrahedron surrounded by twelve 

MO 6 octahedra, i.e. {M 3 O 13 }. These “triads” are linked by shared corners to 

each other and to the central [XO 4 ] tetrahedron (Figure 1.3). 

9


Figure 1.3 The [XM 12 O 40 ] n- Keggin structure in polyhedral representation: 

four corner shared {M 3 O 13 } triads (depicted in different colours) wrapping the 

central [XO 4 ] tetrahedron. 

Depending on if the Keggin polyanion is based on tungsten or molybdenum, 

there are small differences in terms of how close is the structure to the ideal T d 

symmetry. In the case of Mo there is a displacement in the Mo-O-Mo bonds 

from “short” to “long” that reflects in a reduction of symmetry due to small 

displacements of the molybdenum atoms from the mirror planes of the M 3 

triplets. 1a 

The vast majority of the Keggin polyanions contain molybdenum or tungsten 

as centres, being the heteropolytungstates the more abundant ones likely due 

to its stability in solution against hydrolytically decomposition. On the other 

hand, the range of possibilities for the heteroatom X is rather high, from 

transition metal to main group elements, being the phosphorous and silicon 

the most abundant ones. 

10


The Keggin heteropolyanions constitute the most widely studied kind of 

POMs and they are by far the ones with the largest number of applications at 

a great extent due to their acceptor-donor electron and proton properties. 42 

Theoretical studies performed on POM structures revealed that the majority 

of the metallic centres are attached to the most basic oxygen atoms; 43 in the 

case of the Keggin structure are the bridge ones, on the other hand, the same 

studies revealed that the basicity increases with the net charge of the XO 4 

specie due to addition of polarization on the M 12 O 36 neutral sphere. 44 

Therefore, the proton acceptor capacity of heteropolytungstates and – 

molibdates is rather similar, while such capacity is slightly basic for the later. 

On the other hand, the basicity is also affected depending on the heteroatom 

present in the polyanion, e. g. P V


When the polyanion experiences a reduction of more than two electrons, a 

series of structural changes take place. In the case of heteropolymolybdates, 

the protonation takes place on the bridge oxygen atoms of the blue species, 

allowing the isomerisation of the POM to a more stable form, 50 while for the 

protonated blue heteropolytungstates an intramolecular re-arrangement takes 

place in order to generate the so called brown species, where the electrons are 

localized in one of the trimers. 51 The resulting polyanion consist of three triads 

with tungsten in its oxidation state +6, and one in +4, precisely in this trimer 

the terminal oxygen atoms are substituted by water molecules and the 

tungsten atoms are linked through metal-metal bonds. 52 Further reduction 

produces a Keggin polyanion with four W IV triads while each triad can 

accommodate non bonding electron pairs up to a maximum of 32. 53 

1.2.3.2 Isomeric Forms of the Keggin Heteropolyanion: Baker Figgis Isomers 

Keggin heteropolyanions can have up to five structural isomers called Baker- 

Figgis. 54 The structure represented in Figure 1.4 (a) is the α isomer (T d 

symmetry) and by 60° consecutive rotation of 1, 2, 3 and 4 {M 3 O 13 } triad 

further isomers are obtained, namely the β, γ, δ, and ε of C 3v , C 2v , C 3v and T d 

symmetry respectively. 

12


Figure 1.4 The five Baker-Figgis isomers of the Keggin polyanion. Rotated 

{M 3 O 13 } triads are represented in dark red polyhedra. 

The γ, δ and ε isomers are less stable than the α and β, isomer, since the former 

have more triads that share corners, and therefore less M-O-M almost linear 

bonds, hence less dπ-pπ interactions. 55 

López et al. proved by means of theoretical calculations that the neutral 

sphere {M 12 O 36 } of the β isomer is more polarisable than the α isomer due to 

its reduced symmetry in comparison to that of the α isomer, hence the 

stability of the β isomer depends on the heteroatom in [XO 4 ] or the net charge 

of the polyanion. 56 Based on that, for heteropolymolybdates as well as for 

heteropolytungstates the stability increases accordingly to the extent of 

polarisation: X = Al III > Si IV > P V . It has been proved experimentally that for 

the phosphotungstates the isomerisation takes place spontaneously and 

consequently the β isomer can not be isolated, while for the silicotungstates 

isomerisation proceeds slow enough so isolation of β species can be isolated 

and for the aluminotungstates both α and β species exist in equilibrium. 57 13


The Baker-Figgis isomers can be easily identified and characterized by means 

of UV, Infrared, Raman and NMR spectroscopy 58 and specially through 

polarography, since the reduction potential increases with the number of 

rotated trimers. 59 

1.2.3.3 Lacunary Species of the Keggin Heteropolyanion 

Lacunary or vacant species derived from the Keggin structure are generated 

from the α ,β, and γ Baker-Figgis isomers through elimination of a variable 

number of octahedra, giving a total of nine known vacant species. 

1.2.3.4 Lacunary Species derived from the [α-XM 12 O 40 ] n- isomer 

The [α-XM 12 O 40 ] n- Keggin heteropolyanion generates three lacunary species by 

elimination of (a) one octahedron: [α-XM 11 O 40 ] n- , (b) a corner-shared triad: 

[A-α-XM 9 O 40 ] n- and (c) an edge-shared triad [B-α-XM 9 O 40 ] n- 57(a), 60 (Figure 1.5). 

Figure 1.5 The mono- and trilacunary species derived from the [α-XM 12 O 40 ] n- 

Keggin heteropolyanion. 

14


As noted in the previous paragraph, the letter A is placed before the α in order 

to distinguish that the eliminated triad was a corner-shared, opposite to the 

edge-shared that by convention is represented by the letter B. 

1.2.3.5 Lacunary Species derived from the [β-XM 12 O 40 ] n- isomer 

In the case of the β isomer, its reduced symmetry in terms of non-equivalent 

octahedra results in more lacunary species than those of the α isomer. By 

elimination of one octahedron three monolacunary species are known, i.e. β 1 , 

β 2 and 

β 3 . The monovacant β 1 specie is generated by elimination of an 

octahedron opposite to the rotated triad, while the β 2 specie is produced by 

eliminating one octahedron from the middle M 6 O 27 belt. Finally, the β 3 

monolacunary specie is generated by removal of one octahedron from the 

rotated triad (Figure 1.6). 57(a), 60 

Figure 1.6 The three monolacunary species derived from the [β-XM 12 O 40 ] n- 

Keggin heteropolyanion. 

15


As depicted in figure 1.7, there are two known trilacunary species derived 

from the β isomer, namely the A-β and the B-β. The former is generated by 

eliminating the {M 3 O 13 } triad opposite to the rotated one (the only cornershare 

triad), while the later is produced when any {M 3 O 13 } triad is removed 

but the rotated one (an edge-shared triad). 60(b) 

Figure 1.7 Trilacunary species derived from the [β-XM 12 O 40 ] n- Keggin 

heteropolyanion. 

1.2.3.6 Lacunary Species derived from the [γ-XM 12 O 40 ] n- isomer 

There is only one lacunary specie observed from the γ isomer, namely the 

dilacunary [γ–XM 10 O 36 ] m- which is obtained by removing one octahedron from 

each {M 3 O 13 } rotated triad, as depicted in figure 1.8. 61 16


Figure 1.8 [γ-XM 10 O 36 ] m- . The only lacunary specie derived from the 

[γ-XM 12 O 40 ] n- Keggin heteropolyanion. 

The saturated Keggin polyanion [α-XM 12 O 40 ] n- is normally stable at low pH 

values (< 2.0), therefore by increasing the pH removal of tungsten atoms takes 

place generating the lacunary species. On the other hand, the countercation 

plays also an important role in terms of the stability and/or structural type of 

the resulting unsaturated specie. Vacant species are obtainable also from 

simple tungstate salts (Na 2 WO 4 ·H 2 O) and the corresponding oxoacid or 

alkaline salt for the heteroatom. The most straight-forward synthetic method 

for lacunary species of the Keggin anion (and for other kind of polyanions) 

consists in the acidification of an aqueous mixture of the metal oxo-anion and 

the suitable form of the heteroatom. 1e 

Other factors needed to be taken into consideration regarding the synthetic 

procedure are: i) Molecular ratio M/X; which is normally close to the 

stoichiometric ratio. ii) Temperature; which ranges from room conditions to 

hydrothermal methods, pressure does not seem to play an important role. iii) 

Final pH value; this factor is very important since there is normally a range of 

pH values at which a given specie is stable before decomposing or 

transforming to another. iv) Solvent; sometimes the stability is improved by 

addition of small amounts of organic solvents, and finally v) Nature of the 

countercations; the formation of some species are at a high extent governed 

by the countercation, e.g. the divacant [γ-PW 10 O 36 ] 7- polyanion is known only 

17


as a caesium salt. Since isolation of POMs in the solid state is of particular 

importance for their identification and structural characterization, and having 

in mind that sometimes several species can be present in solution, the choice 

of the adequate countercation would lead to the precipitation of the 

heteropolysalt either direct in crystalline form or as an amorphous 

precipitate. 1g 

1.2.4 The Wells-Dawson [X2W18O62] 6- (X = P V , As V ) Heteropolyanions 

and its lacunary species from the α isomer 

This class of heteropolyanions are only known with P V and As V and they 

result from the direct union of two [A-α-XW 9 O 34 ] or two [A-β-XW 9 O 34 ] 

trilacunary Keggin units through the six-oxygen upper crown. Association of 

two A-α units results in the α isomer (Figure 1.9), whereas one A-α and one 

A-β generates the β isomer and finally two A-β produces the γ isomer. 

Moreover, rotation by 60° of one of the two units leads to the α*, β* and γ* 

frameworks, respectively. 62 In fact, only four of them are known up to date, 

namely the α, β, γ and γ*, the last one only known with arsenic. 

Figure 1.9 The Wells-Dawson [α-X 2 W 18 O 62 ] 6- (X = P V , As V ) heteropolyanion. 

18


1.2.4.1 Lacunary Species derived from the [α-X 2 W 18 O 62 ] 6- isomer 

Like the Keggin polyanions, the Wells-Dawson species have as well isomers 

and vacant species. Only the α isomer produces stable lacunary species. Two 

monolacunary species are known, namely the α 1 and α 2 that are obtained by 

elimination of one octahedron from the central double-belt, or one from the 

{M 3 O 13 } trimers [α 1 -X 2 W 17 O 61 ] 10- and [α 2 -X 2 W 17 O 61 ] 10- respectively (Figure 

1.10). 62 (a) (b) 

Figure 1.10 Monolacunary species of the Wells-Dawson polyanion 

(a) [α 1 -X 2 W 17 O 61 ] 10- , (b) [α 2 -X 2 W 17 O 61 ] 10- . 

By removing one {M 3 O 13 } trimer, the trilacunary [P 2 W 15 O 56 ] 12- is formed 

whereas elimination of four octahedra from the central double-belt plus one 

of each trimer results in the hexalacunary [H 2 P 2 W 12 O 48 ] 12- (Figure 1.11). 63 19


(a) 

(b) 

Figure 1.11 Tri- and Hexalacunary species of the Wells-Dawson polyanion 

(a) [P 2 W 15 O 56 ] 12- , (b) [H 2 P 2 W 12 O 48 ] 12- . 

1.2.5 The Henicosatungstodiphosphate and –arsenate 

[X2W21O71(H2O)3] 6- (X = P V , As III ) polyanion and their mono- und 

dilacunary derivatives 

When two [A-α-PPV W9O 34] 

units or two [B-α-As III W9O 33] units are bridged by 

three octahedrally coordinated W atoms located in the equatorial plane in 

sites that correspond to those of the α Keggin isomer, the [X W O (H O) ] 

(X = P V , As III ) species are formed (Figure 1.12). 

1, 57b, 64 

2 21 71 2 3 n- 

20


(a) 

(b) 

Figure 1.12 [X 2 W 21 O 71 (H 2 O) 3 ] n- , (a) X = P V , (b) X = As III . 

Each equatorial octahedron shares four oxygen with both [A-α-XW 9 O 34 ] 9- or 

[B-α-As III W 9 O 33 ] groups and is completed with one oxygen and one water 

molecule in the equatorial plane. Surprisingly, this three bridging tungsten 

atoms does not conform to the C 3v symmetry corresponding to the [A-α- 

XW 9 O 34 ] 9- unit, since one tungsten atom is displaced farther from its axis, 

while the other two equivalents are slightly nearer. 1c 

1.2.5.1 The monolacunary [P 2 W 20 O 70 (H 2 O) 2 ] 10- polyanion 

Elimination of one tungsten from the equatorial belt results in the 

monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- polyanion. According to several 

crystallographic studies from independent groups, 65,66 the vacancy in the 

potassium salt of the [P 2 W 20 O 70 (H 2 O) 2 ] 10- polyanion is filled with a K + cation 

trapped within six oxygen of the anion (Figure 1.13) 

21


(a) 

(b) 

(a) 

(b) 

Figure 1.13 The monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- polyanion with a potassium 

cation in the cavity. (a) Front view, (b) Side view. 

High-resolution 183 W NMR spectra of Li + , Na + and Ca + salts show a 

substantial dependence on the cation and well support the results of the 

structural study. 64,65,67 The spectrum consist of six signals with relative 

intensities 1:2:2:2:2:1.Based on this results, it was concluded that each half of 

the polyanion contains four different tungsten pairs and a unique tungsten 

atom in the polar cap with two equivalent belt tungsten atoms connecting the 

polyanion halves. 66 The crystal structure and absence of splitting of one 183 W 

NMR signal in mixed H 2 O-D 2 O prove that both aqua ligands are located on 

the exterior of the polyanion. 1c 

The arsenate (V) homologue has also been synthesized and its 183 W NMR 

spectrum reported by Contant et al. 68 Fuchs et al. 69 identified and studied a 

structure also with the P 2 W 20 composition, but strongly different from the 

described above, namely [P 2 W 20 O 72 ] 14- . Even when a K + is also trapped in the 

vacancy, the Fuch´s structure is formed by two [A-α-PW 9 O 34 ] 9- groups bridged 

by two tungstic octahedra sharing cis-positioned oxygen atoms with both [A- 

22


α-PW 9 O 34 ] 9- units (instead of para-), also the charge of this polyanion is 

different, namely 14-. 

1.2.5.2 The dilacunary [X 2 W 19 O 69 (H 2 O)] n- (X = P V , As III ) polyanion 

The divacant [P 2 W 19 O 69 (H 2 O)] 14- polyanion as well as some of its properties 

was first described in 1977 by Tourné et al. 70 but the crystal structure of its 

potassium salt was first determined in 1988. 65 In this divacant polyanion, only 

one (WO 5 OH 2 ) octahedron bridges the two [A-α-PW 9 O 34 ] 9- groups and the 

structure is maintained rigid with two K + cations and two internal water 

molecules. In solution this cluster seems to degrade according to some 31 P 

NMR studies conducted by Tourné et al. 1c Kortz et al. 71 reported a synthetic 

procedure as well as a structural characterization of the divacant 

[As III 2W 19 O 67 (H 2 O)] -14 mixed K-Na-Ni salt (Figure 1.14). Existence of the 

{As V 2W 19 } homologue was reported in a general scheme relating the α-species 

{AsW 9 }, {AsW 11 }, {As 2 W 20 } and {As 2 W 21 } in K + media, but synthesis 

procedures were not indicated. 68 

(a) 

(b) 

Figure 1.14 The divacant [As 2 W 19 O 69 (H 2 O)] 14- polyanion with four potassium 

cations in the cavity. (a) Front view, (b) Side view. 

23


1.3 Applications 

1.3.1 Catalysis 

The area where perhaps the most applications for POMs are to be found is in 

the realm of acid and oxidation catalysis. Their stability, redox reversibility 

and high acidity are all properties that can be modified trough compositional 

variations. On the other hand, they have a proven versatility to be used 

directly or supported and they have found use in homogeneous and 

heterogeneous processes. 72, 73 

POMs can be used in the selective and controlled oxidation of alcohols to 

alkanes, aldehydes or carboxylic acids, as well as in dehydrogenation 

processes to alkenes and their epoxidation. Regarding heterogeneous 

processes; of great industrial importance is the synthesis of methacrylic acid 

from oxidation of methacrolein or isobutene. On the other hand, 

polyoxometales have already proved promising results in the sulfoxidation of 

organic molecules at standard temperature and pressure conditions as green 

catalysators for elimination of toxic agents in the air. 74,75,76 

Controlled oxidation of arenes and alcohols, as well as alkenes and ketones 

using the Wacker method count among the most important homogeneous 

catalytic processes using POMs. 77 POMs have prove their usefulness in the 

electrocatalytic reduction of ammonium nitrate and in green industrial wood 

practices. 78 

POMs substitute mineral acids as acid catalysators based on their superior 

catalytic activity and cleanness, therefore they are used in the dehydration of 

alcohols and olefins hydration. 79 24


Industrial production of 2-propanol, 2-butanol and t-butanol from olefins is 

catalysed with phosphotungstic acid, however, hydrodesulfurization of fossil 

fuels is the most important industrial application of POMs. 80 

1.3.2 Medicine 

An important number of POMs confirm biological activity due to their 

stability at physiological pH as well as their size, shape and electron- acceptor 

capability allows them to block the active centres of biomolecules. 81 

Based on the above mentioned characteristics, over the past few decades an 

important effort has been done in order to synthesize functionalized 

polyoxoanions with pharmacological interest. 82 

It has been observed, that POMs can inhibit or selectively activate a given 

number of enzymes, like dehydrogenase, phosphorylase, and protease. 83 

Another important feature consists of their capability to mimetize protein 

activity like insulin, as already some promising results have been reported in 

experiments conducted with diabetic mice. 84 As anti-carcinogenic agents they 

have shown some satisfactory results against a number of tumours; however, 

potential applications as antiviral and anti retroviral agents have generated 

the most interest, since they have already shown activity against a broad 

spectrum of virus, like herpes and retrovirus like the HIV in none citotoxic 

dosage; the latter in vivo as well as in vitro. 85 25


1.3.3 Hybrid Organic-Inorganic Materials 

Research in the area of hybrid organic-inorganic materials has been 

experiencing a growing interest based on their novel properties based on the 

synergy of their constituents. POMs constitute an ideal class of compounds 

for this purpose since they can be easily functionalized and assembled in a 

controlled fashion. Hence the systematic derivatization of POMs can lead to 

assemblies with novel structures and may allow for a rational design of 

tailored catalytic systems, an increase of the selectivity to specific targets, or 

other unexpected synergistic effects. Substituted polyanions are also 

interesting building blocks for crystal engineering because they can establish a 

variety of networks of intermolecular interactions so that their properties and 

applications could be influenced. 86 

Incorporated dendrimers to POM frameworks, as well as polyaniline, 

polacrilin and polypyrrole polymers with POMs covalently attached or as 

bridges between chains or as part of the main chain are some examples of 

functionalized organic-inorganic materials already used in catalysis. 87 

Introduction of this class of clusters in polymeric organic matrices permit the 

synthesis of nanocomposite materials of well defined structure, as ultrafine 

films either multi-layer or Langmuir-Blodgett type. 88 Prospective purposes 

due to the versatility of this category of compounds can range from solid 

batteries, sensors and electrodes. POMs functionalized with organotin and – 

antimony groups have potential applications as anti-fouling agents since the 

organometallic group is attached to the polyoxometallic framework, hence 

permitting a reduced level of toxicity. 89 

26


1.4 State of the Art on Organotin and –antimony Functionalized 

Polyoxoanions 

In its widest acceptation, functionalization of POMs may consist of replacing 

one, or several, metal-oxo function(s) by a new one, where the metal and/or 

the oxo ligand have been changed. If terminal oxo ligands are mainly replaced, 

some examples are also known of formal replacement at the bridging sites. 

Functionalization of POMs may also consist in the grafting of a functional 

group at the surface of the polyanion. 1g 

The functionalization of POMs with organometallic moieties covalently 

attached to the metal-oxo framework constitutes an emerging area of interest 

because the resulting hybrid species combine the unique features of both 

components. Nevertheless, the structure-activity-application relation is not 

yet fully understood, and therefore the synthesis of new hybrid organicinorganic 

polyanions (as well as the complete structural characterization of 

known species) remains an important research objective. Organotin groups 

are good candidates for the derivatization of POMs because the size of Sn(IV) 

is appropriate to substitute addenda metal centers in POM skeletons and also 

because the Sn-C bond shows a relatively high stability to hydrolysis in 

aqueous media. 

1.4.1 Monoorganotin Functionalized POMs 

1.4.1.1 Knoth´s Work 

Knoth reported in the late seventies the first Keggin derivatives, 

[XM 11 O 39 (SnR)] n- (X = Si IV , P V ; M = Mo, W; R = CpFe(CO) 2 , 

p-FC 6 H 4 Pt[P(C 2 H 5 ) 3 ] 2 , nevertheless no crystal structure was reported. 90 By the 

same time, Zonnevijlle and Pope 91 described the first monoorganotin 

functionalized Wells-Dawson derivative, [P 2 W 17 O 61 (SnR)] 7- where R = n-Butyl. 

27


In 1983 Domaille and Knoth 92 reported the synthesis and solution properties 

by means of 183 W and 31 P NMR of [CpFe(CO) 2 Sn] 2 PW 10 0 38 ] 5- and two years 

later a series of sandwich complexes [(RSnOH 2 ) 3 (PW 9 O 34 )] 9- [R = Ph, 

CpFe(CO) 2 ] characterized by infrared spectroscopy and multinuclear NMR, 

however, no crystallographic studies were conducted and their structures 

were only proposed. 

1.4.1.2 Pope´s Work 

By the middle nineties, Pope and co-workers studied the interaction of RSn 3+ 

(R = n-C 4 H 9 , C 6 H 5 ) electrophiles toward A-α- and A-β-trilacunary Keggin 

tungstosilicates, tungstophosphates as well as trilacunary Wells-Dawson 

polyanions. These species were fully studied in solution by multinuclear 

NMR techniques; and most of them by single-crystal X-ray diffraction, 

infrared spectroscopy and elemental analysis (Figure 1.15). 93 

Figure 1.15 The sandwich type [(BuSnOH) 3 (α-SiW 9 O 34 ) 2 ] 14- polyanion. 

28


In 2000, Pope and co-workers 94 reported the tris(phenyltin)-substituted 

tungstoantimonate(III) Cs 6 [(PhSn) 3 Na 3 (α-SbW 9 O 33 ) 2 ]·20H 2 O and the tetrakis- 

(phenyltin)-substituted tungstoarsenate(III) Na 9 [{(PhSn) 2 O} 2 H(α-AsW 9 O 33 ) 2 ] 

·20H 2 O, which were prepared by reaction of phenyltin trichloride with Na 9 [α- 

SbW 9 O 33 ]·19.5H 2 O and Na 9 [α-AsW 9 O 33 ]·19.5H 2 O, respectively, in aqueous 

solution. The products were characterized by elemental analysis, X-ray 

crystallography, multinuclear NMR, and infrared spectroscopy (Figure 1.16) 

Figure 1.16 The sandwich type [(PhSn) 3 Na 3 (α-SbW 9 O 33 ) 2 ] 6- polyanion. 

Four years later, fifteen Keggin-anion-derived polytungstates 

[TW 11 O 39 {MCH 2 CH 2 X}] n- (T = Si, Ge, Ga; M = Sn, Ge; X = COOH, COOCH 3 , 

CONH 2 , CN; n = 5, 6) were prepared in aqueous or aqueous–organic solution 

from the corresponding lacunary polytungstates and trichlorotin and – 

germanium precursors, and were isolated as caesium salts 95 . The derivatized 

polytungstates were characterized by elemental analysis, multinuclear NMR 

spectroscopy, and cyclic voltammetry; and they found to be stable in aqueous 

solution to pH 6–7. NMR spectroscopy revealed the presence of a second (β 1 

29


or β 3 ) isomer in the tungstogallate derivatives. Acid hydrolysis of the ester 

and nitrile derivatives could be achieved without decomposition of the 

polytungstate moieties, and esterification and amidation of the carboxylate 

functions was straightforward using standard coupling techniques, e.g. the 

formation, isolation and characterization of 

[SiW 11 O 39 {Ge(CH 2 ) 2 CONHCH 2 COOCH 3 }] 5- from glycine methyl ester. Since 

the Cl 3 MCH 2 CH 2 X precursors are readily accessible by 

hydrostannation/germanation reactions with the corresponding alkenes, 

novel coupled polytungstates, such as [(SiW 11 O 39 GeCH 2 CH 2 COOCH 2 ) 4 C] 20- 

from pentaerythritol tetraacrylate, could also be prepared. 

The last reported work of Pope and co-workers consisted in the synthesis and 

structural characterization of new organotin derivatives of polyoxotungstates 

via transmetallation and coupling reactions. 96 Organotin-substituted POMs 

[WM(RSn) 2 (MW 9 O 34 ) 2 ]10-; (M= Co, Zn; R = CH 3 , C 2 H 5 , n-C 4 H 9 ) were 

prepared through exchange reaction of [WM 3 (H 2 O) 2 (MW 9 O 34 ) 2 ] 12- and the 

appropriate organotin trichloride in aqueous solution. The complexes were 

characterized in solution by 183 W and 119 Sn NMR spectroscopy of the 

diamagnetic anions, and by single crystal structure determinations of salts of 

the methyl, ethyl and n-butyl derivatives of the tungstozincates and of the 

methyl derivative of a CoZn 2 analog (Figure 1.17). Cyclic voltammetry 

demonstrates for the first time for this class of POMs that the tetrahedral 

cobalt(II) centres are reversibly oxidizable to yield high-spin cobalt(III) 

analogs. Displacement of the kinetically metastable [W 5 O 18 ] 6- anion from 

[Ce(W 5 O 18 ) 2 ] 10- , by reaction with CH 3 SnCl 3 , leads to modest yields of 

[CH 3 SnW 5 O 18 ] 3- . Bis(trichlorostannyl)alkanes such as Cl 3 Sn(CH 2 ) 4 SnCl 3 can be 

used as covalent linkers of POM anions to form the ‘‘dumbbell’’ complex 

[SiW 11 O 39 Sn(CH 2 ) 4 SnSiW 11 O 39 ] 10- and linear oligomers 

{[(Sn(CH 2 ) 4 Sn)(WZn(ZnW 9 O 34 ) 2 )] 10- } x . 

30


Figure 1.17 [(n-C 4 H 9 Sn) 2 Zn 2 (B-α-PW 9 O 34 ) 2 ] 8- (green balls represent Zn atoms 

and black carbon. Hydrogen omitted for clarity). 

1.4.1.3 Hasenknopf´s Work 

Recently, Hasenknopf and co-workers reported several Wells-Dawson 

functionalized POMs with organotin moieties in organic and aqueous media, 

i.e [α 1 -P 2 W 17 O 61 {SnR] n- and [α 2 -P 2 W 17 O 61 {SnR] m- (R = CH 2 COOH, CH 2 COOEt, 

CH=CH 2 , CH 2 CHO, CH 2 COOMenthyl, (CH 2 ) 2 CO 2 H) such compounds were 

characterized by multinuclear NMR and infrared spectroscopy, whereas no 

crystal structure were reported. Scheme 1.1 depicts their proposed mechanism 

for Wells-Dawson type functionalization. 97, 98 31


Scheme 1.1 Preparation of Functionalized Wells-Dawson Polyoxotungstates. 98 

Hasenknopf reported a copper-catalyzed azide/alkyne cycloaddition with the 

objective to graft any kind of organics (lipophilic, water-soluble, biologically 

relevant) to polyoxotungstates to generate hybrids. The method was argued 

not to be limited by solvent matching between the polyoxometallic platforms 

and the organic substrates. In any case, no crystal structure was reported in 

this work and only solution studies support their findings. 99 

1.4.1.4 Liu´s Work 

Besides the synthesis of new organotin functionalized POMs based on mono-, 

di- and trilacunary Keggin vacant polyanions, Liu worked briefly in their 

antitumoral activity, nevertheless such findings are far of being conclusive 

and only a brief description of the experimental procedure is described 

without discussing the results in relation to other antitumor agents. On the 

other hand, no crystallographic studies were conducted in any of his new 

32


functionalized polyanions, being characterized only by elemental analysis and 

other spectroscopic methods in the solid state and in solution. 100 

1.4.1.5 Krebs´ Work 

Prof. Bernt Krebs from the University of Münster, Germany, investigated the 

interaction of organotin electrophiles towards molybdates, resulting in the 

novel [(Ph 2 Sn) 2 (μ-OH) 2 (μ-MoO 4 ) 2 ] 2- molecular organotin molybdate. 1c This 

anion consists of two MoO4 tetrahedra bonded to two octahedrally 

coordinated tin atoms, i. e. a four-membered [Sn-O(H)-Sn-O(H)] ring which is 

capped on both sides by a tetrahedral MoO 4 unit. In addition to two bonds 

that bridge the molybdate ligands and two that bridge OH groups, each tin 

atom has two Sn-C bonds to phenyl rings to complete a distorted octahedral 

cis-Ph 2 SnO 4 coordination. 

Another interesting novel compound based on the lacunary Lindqvist 

[W 5 O 18 ] 6- isopolyanion was obtained by Krebs and co-workers by reaction of 

(n-Bu 4 N) 2 [WO 4 ] in acetonitrile with PhSnCl 3 and HCl with addition of 

diethylether. The resulting polyanion may be described as a molecular 

arrangement of five distorted edge-sharing WO 6 octahedra and one PhSnO 5 

polyhedron. The six metal atoms are located octahedrally around a central 

oxygen atom. In summary, the [PhSnW 5 O 18 ] 3- polyanion structure is derived 

from the [W 6 O 19 ] 2- ion by replacement of a WO 4+ by a PhSn 3+ unit. This 

polyanion represented the first molecular organotin compound based on a 

isopolytungstate, namely the Lindqvist ion. 1c 33


1.4.2 Diorganotin Functionalized POMs 

1.4.2.1 Kortz´s Work 

Starting in 2003, Kortz and co-workers have been investigating the interaction 

of diorganotin electrophiles with a multitude of vacant polyanions 

demonstrating that the R 2 Sn 2+ group act as a higly efficient linker of lacunary 

heteropolytungstates as well as isopolytungstates resulting in assemblies with 

unprecedented architectures. These include discrete molecular dimeric and 

trimeric species, tetrameric cagelike assemblies, dodecameric superlarge 

POMs, and 1- and 2D materials. 

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) ∞ and the 

isostructural (CsNa 4 [(Sn(CH 3 ) 2 ) 3 O(H 2 O) 4 (β-SbW 9 O 33 )]·5H 2 O) ∞ . Both structures 

were synthesized and characterized by multinuclear NMR spectroscopy, FT- 

IR spectroscopy and elemental analysis. Multinuclear NMR ( 183 W, 119 Sn, 13 C, 

1 H) showed that both compounds 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 , Sb III ) 

respectively. Both polyanions consist of a (β-XW 9 O 33 ) fragment which is 

stabilized by three dimethyltin fragments. 101 

Shortly afterwards, a 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 ] 21- species , composed of four (Bα-AsW 

9 O 33 ) fragments that are linked by three dimethyltin groups and three 

As(III) atoms were synthesized and characterized in the solid state and in 

solution by multinuclear NMR techniques, resulting in a chiral polyoxoanion 

assembly with C 1 symmetry. 102 34


The breakthrough in terms of size and connectivity features of organotin 

functionalized POMs came with the discovery in 2005 of the dodecameric, 

ball-shaped anion [{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 ) 

composed of 12 trilacunary [A-XW 9 O 34 ] 9- 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 (Figure 

1.18) Several other properties of this polyanion were also investigated, i.e. 

stability, redox and electrocatalytic properties in aqueous media as well as 

STM/STS observation on HOPG surfaces. 103 

Figure 1.18 The dodecameric [{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 ) polyanion. Blue balls represent tin, green (carbon), red (oxygen), 

red octahedra (WO 6 ) and yellow tetrahedral (XO 4 ). 

Interaction of diorganotin electrophiles toward molybdates were also studied 

in the Kortz group as reported in 2006, where reaction of (CH 3 ) 2 SnCl 2 with 

Na 2 MoO 4 in an aqueous medium results in three different compounds 

depending on the pH: [{(CH 3 ) 2 Sn}(MoO 4 )], [{(CH 3 ) 2 Sn} 4 O 2 (MoO 4 ) 2 ], and 

35


[{(CH 3 ) 2 Sn}{Mo 2 O 7 (H 2 O) 2 }]·H 2 O . All three species were characterized in the 

solid state by means of elemental analysis, infrared spectroscopy, 

thermogravimetry, and single-crystal X-ray diffraction. All the 

abovementioned compounds show hybrid organic-inorganic extended lattices 

based on molybdate anions linked by (CH 3 ) 2 Sn 2+ moieties, and the 

coordination numbers of the Sn(IV) centers range from 5 to 7. 104 

The first evidence for a lacunary Preyssler fragment, as Kortz and Pope 105 

argue in their report from 2006, is based on the product of reacting the 

superlacunary polyanion [H 2 P 4 W 24 O 94 ] 22- with electrophiles. One pot reaction 

of this precursor polyanion with dimethyltin dichloride in aqueous acidic 

medium resulted in the hybrid organic-inorganic 

[{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ] 28- .Single-crystal X-ray analysis was carried out on 

K 17 Li 11 [{Sn-(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ]·51H 2 O. Such polyanion is composed of 

two (P 4 W 24 O 92 ) fragments that are linked by four equivalent diorganotin 

groups (Figure 1.19). This unprecedented assembly has D 2d symmetry and 

contains a hydrophobic pocket in the centre of the molecule. 

Figure 1.19 The [{Sn(CH 3 ) 2 } 4 (H 2 P 4 W 24 O 92 ) 2 ] 28- polyanion. Colour code is the 

same as Figure 1.16. 

36


The versatility of the dimethyltin electrophile as a linker between polyanion 

“building blocks” was again confirmed by the reaction of Na 2 WO 4 and 

(CH 3 ) 2 SnCl 2 in water (pH 7), resulting in the formation of the hybrid organicinorganic 

polyanion [{(CH 3 ) 2 Sn} 2 (W 6 O 22 )] 4- ,which is composed of a novel 

hexatungstate core stabilized by two dimethyltin groups. Selective 

crystallization of the abovementioned polyanion with guanidinium cations 

resulted in [C(NH 2 ) 3 ] 4 [{(CH 3 ) 2 Sn} 2 (W 6 O 22 )]·2H 2 O, which exhibits a 1D 

arrangement via distorted trigonal-bipyramidal cis-(CH 3 ) 2 SnO 3 moieties. 106 

During 2007, Kortz et al. reported a trimeric, cyclic dimethyltin-containing 

tungstophophate [{(Sn(CH 3 ) 2 )(Sn(CH 3 ) 2 O)(A-PW 9 O 34 )} 3 ] 21- which was 

synthesized in aqueous acidic medium and characterized by IR, elemental 

analysis, electrochemistry, and FT-ICR MS and single-crystal X-ray 

analysis. 107 Such polyanion is composed of three trilacunary (A-PW 9 O 34 ) 

Keggin fragments that are linked on one side via three isolated dimethyltin 

groups and on the other side by a [Sn 3 (CH 3 ) 6 O 3 ] unit and three cesium ions, 

resulting in a cyclic assembly with C 3v symmetry. 

Studies carried out with the elusive [H n BW 13 O 46 ] (11-n)- species towards 

dimethyltindichloride resulted in the novel dimethyltin-containing polyanion 

[{(CH 3 ) 2 Sn} 6 (OH) 2 O 2 (H 2 BW 13 O 46 ) 2 ] 12- , composed of two [H 2 BW 13 O 46 ] 9- clusters 

linked by an unprecedented planar, hexameric [{(CH 3 ) 2 Sn} 6 (OH) 2 O 2 ] 8+ 

organostannoxane moiety, representing the first X-ray structural 

characterization of a molecular hybrid organic-inorganic tungstoborate 

(Figure 1.20). 108 37


Figure 1.20 The [{(CH 3 ) 2 Sn} 6 (OH) 2 O 2 (H 2 BW 13 O 46 ) 2 ] 12- polyanion. 

Kortz and co-workers decided to carry out a study on the reactivity of RSn 3+ 

electrophiles toward 9-tungstogermanates to identify the similarities and 

differences between both RSn 3+ /[XW 9 O 34 ] 10- (X = Ge IV , Si IV ) systems. They 

resoluted to reinvestigate the reactivity for the 9-tungstosilicate analogues to 

complete the solid state characterization of these hybrid polyanions, since 

previous work by Pope 93b also on these systems were incomplete. 

This investigation resulted in the synthesis, solution and solid state structures 

of the first trilacunary Keggin tungstogermanate functionalized with 

organotin units, [{(C 6 H 5 )Sn(OH)} 3 (A-α-GeW 9 O 34 )]4- ,and of two organotincontaining 

9-tungstosilicates, [{(C 6 H 5 )Sn(OH)} 3 (A-α-SiW 9 O 34 )] 4- and 

[{(C 6 H 5 )Sn(OH)} 3 (A-α-H 3 SiW 9 O 34 ) 2 ] 8- . 

The above mentioned polyanions were isolated in the form of five different 

compounds by reaction of (C 6 H 5 )SnCl 3 with Na 10 [A-α-XW 9 O 34 ]· 18H 2 O 

(X = Si IV , Ge IV ) in water: Cs 3 Na[{(C 6 H 5 )Sn(OH)} 3 (A-α-GeW 9 O 34 )]· 9H 2 O , 

Cs 3 [{(C 6 H 5 )Sn(OH)} 3 (A-α-HGeW 9 O 34 )]·8H 2 O , Cs 3 Na[{(C 6 H 5 )Sn(OH)} 3 (A-α- 

SiW 9 O 34 )] · 9H 2 O , Cs 4 [{(C 6 H 5 )Sn(OH)} 3 (A-α-SiW 9 O 34 )] · 13H 2 O,as well as 

Cs 8 [{(C 6 H 5 )Sn(OH)} 3 (A-α-H 3 SiW 9 O 34 ) 2 ]·23H 2 O. The compounds were 

38


characterized in the solid state by means of single-crystal X-ray diffractometry, 

FT-IR, thermogravimetry and in solution by multinuclear NMR. 109 The first of 

the above mentioned polyanion, the so called “flower pot” is depicted in 

Figure 1.21. 

Figure 1.21 The flower pot [{(C 6 H 5 )Sn(OH)} 3 (A-α-GeW 9 O 34 )] 4- polyanion (olive 

green balls represent tin atoms, whereas black are carbon, light gray hydrogen, 

red oxygen and yellow the central germanium. 

39


1.4.3 Organoantimony Functionalized POMs 

The chemistry of organoantimony functionalized POMs is quite scarce in 

comparison to that of organotin. In 1989, the group of Liu (different from the 

one that worked with monoorganotin-POM compounds) reported on the 

solid state structure of [(Ph 2 Sb) 2 (μ-O) 2 (μ-MoO 4 ) 2 ] -2 , in which two separated 

MoO 4 tetrahedra bridge two octahedrally coordinated antimony atoms. 110 A 

few years later, Krebs and co-workers prepared the isostructural tungsten 

analogue. Recently, Winpenny’s group synthesized a reverse Keggin ion 

comprising 12 PhSb units in the addenda positions and a central MO 4 (M = 

Mn, Zn) tetrahedron 111 (more structural details of the above mentioned 

compounds are found in Chapter VIII). 

40


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45, 761. 

(106) Reinoso, S.; Dickman, M. H.; Kortz, U. Inorg. Chem. 2006, 45, 10422. 

(107) Hussain, F.; Dickman, M. H.; Kortz, U.; Keita, B.; Nadjo, L.; Khitrov, G. 

A.; Marshall, A. G. J. Cluster Sci. 2007, 18, 173. 

(108) Reinoso, S.; Dickman, M. H.; Matei, M.; Kortz, U. Inorg. Chem. 2007, 46, 

4383. 

(109) Reinoso, S.; Dickman, M. H.; Praetorius, A.; Piedra-Garza, L. F.; Kortz, 

U. Inorg. Chem., 2008, 47, 8798. 

(110) Liu, B.-y.; Ku, Y.-t.; Wang, M.; Wang, B.-y.; Zheng, P.-j. J. Chem. Soc., 

Chem. Commun. 1989, 651. 

(111) Baskar, V.; Shanmugam, M.; Helliwell, M.; Teat, S. J.; Winpenny, R. E. P. 

J. Am. Chem. Soc. 2007, 129, 3042. 

52

Chapter II. Analytical Techniques used in the Characterization of POMs and Synthesis of Precursors 

Chapter II. Analytical Techniques used in the Characterization 

of POMs and Synthesis of Precursors 

The complexity of POM systems places extreme demands upon experimental 

techniques and upon interpretation of results. Structural X-ray crystallography 

has played a major role in the development of the field, and is up to date the 

unbeatable choice when it comes to characterization in the solid state. 

Thermogravimetry delivers important information regarding thermal stability 

and brings also information on the species present; nevertheless elemental 

analysis is definitely the method to prove the purity of the bulk product. Also 

FT-Infrared is a very useful technique not only as a “fingerprint” method for 

compounds in the solid state, but also to identify the metal-oxygen bands typical 

for POMs and even more useful if the POM has organometallic groups crafted on 

it. 

On the other hand, major problems remain with the identification and structural 

characterization of species in solution, since more than one complex may be 

present, and only the less soluble specie precipitates as crystalline material. 

Therefore, a battery of different experimental techniques needs to be applied, 

such as the case of cyclic voltammetry or even more useful multinuclear 

magnetic resonance. As Pope in his monograph of 1983 1 described, another 

characterization methods were of common use during the first 20 to 30 years of 

the second half of the twentieth century, methods that are being less and less 

common, such as Equilibrium Analysis, Polarography as well as Diffusion and 

Dialysis. Other more modern techniques are being replacing the oldest ones 

hence being the chemist able to obtain much more information on the true nature 

of the compounds; those include Electron Paramagnetic Resonance, Electronic 

Spectroscopy and X-ray Photoelectron Spectroscopy, just to name a few. 2 53


2.1 Infrared Spectroscopy 

Infrared spectroscopy has been a frequently used technique for the 

characterization of iso- and heteropolyoxometalates, particularly as consequence 

of the identification of the M-O-M (M = central metal in the octahedron). One of 

the first infrared investigations of the heteropolyoxometalates was reported by 

Sharpless and Munday who examined the ammonium salts of 12-tungsto- and 

12-molybdophosphoric, tungstoboric, tungsto- and molybdosilicic, tungsto- and 

molybdoarsenic, molybdomanganic and molybdotitanic acids in potassium 

bromide pellets and provided band assignements. 3 

For the present work, infrared spectra 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. 

2.2 Thermogravimetry 

Thermal stability of heteropolyoxometalates has been studied as a part of 

investigations regarding stability aspects of such materials. One of the earliest 

studies on the thermal stability of POMs was conducted on heteropoly acids by 

West and Audrieth in the middle 1950’s 4 where each of the four acids examined, 

an endotherm and an exotherm are observed at around 300 °C, whereas the low 

temperature endotherm is attributed to the removal of waters while the high 

temperature exotherm signals decomposition of the anion. 

54


Thermogravimetric analyses were performed on a Q 600 device from TA Instruments 

with 10-30 mg samples in 100 μL alumina pans, under a 100 mL/min. N 2 flow with a 

heating rate of °5 C/min. 

2.3 Single Crystal X-ray Diffraction 

The first and most significant contribution of crystal structure analysis to POM 

chemistry is the revelation of the coordination arrangement of the atoms in the 

molecule. For this purpose, all the oxygen atoms must be located. The degree of 

refinement is commonly expressed as the relative first moment of the deviations 

of the scattering amplitudes (observations) from those predicted by a model, the 

reliability factor R: 

R = ∑║F(obs)│ - │F(calc) ║/∑│F(obs)│ Eq. 2.1 

Refinement is usually based on the nonlinear least-squares method of gauss, 

minimizing the value of the numerator of the commonly reported second 

moment, the “weighted R factor” R w : 

R w = ∑w[│F(obs)│ - │F(calc)│] 2 ║/∑ w[F(obs)] 2 Eq. 2.2 

This result yields atomic coordinates, anisotropic (second order) thermal 

parameters and population parameters (percent of atomic vacancies or 

substitutions) for all resolved atoms, together with associated standard errors 

(usually distributed from the original diffractometer counting statistics). The 

final analysis may fail to provide desired information because of problems 

inherent in modelling the structure itself. Three are such common type of 

difficulties: i) Positional disorder, ii) Disordered interstitial material, and iii) 

55


Structures near a singularity. 5 A complete treatment on X-ray crystal diffraction 

is beyond the scope of this work, therefore the reader is advised to check the rich 

literature on this topic for further reading. 

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

single crystal diffractometer equipped with Mo-Kα radiation (λ= 0.71073 Å). Data 

collections, unit cell determinations, intensity data integrations, routine corrections for 

Lorentz and polarization effects, and multiscan absorption corrections were performed 

using the APEX2 software package. 6 The structures were solved and refined using the 

SHELXTL software. 7 Direct or Patterson methods were used to solve the structures and 

to locate the heavy atoms. The remaining atoms were found from successive Fourier 

syntheses. 

2.4 Elemental Analysis 

The most common method to investigate the purity of the bulk precipitated solid 

from a reaction that presumably resulted in the desired POM compound is 

undoubtedly elemental analysis that is performed generally by a commercial 

laboratory. 

All elemental analyses were performed by Analytische Laboratorien Prof. Dr. H. Malissa 

und G. Reuter GmbH, Industriepark Kaiserau (Haus Heidbruch) 51779 Lindlar 

(Nordrhein-Westfalen) Germany. 

56


2.5 Nuclear Magnetic Resonance (NMR) Spectroscopy 

As already described in the introductory paragraphs of this chapter, one of the 

most important techniques used to study polyoxometalates (POMs) in solution is 

based on NMR spectroscopy. There are several nuclei that are of potential 

interest and value for studies of heteropoly and isopolyanions, among others: 11 B, 

17 O, 27 Al, 29 Si, 31 P, 51 V, 71 Ga, 77 Se, 95 Mo, 93 Nb, 183 W, 125 Te, 195 Pt, and so on). 1 Some 

nuclei, such as B, P, Si act as the central atom; some act as ligand atoms (Mo and 

W), and others can act either as central atoms or as ligand atoms (V, Al, Ga, Fe, 

Co, etc.). However, relatively few POMs containing these elements have been 

studied, as yet, by NMR spectroscopy. 

2.5.1 17 O NMR of Polyoxometalates 

The element oxygen is an essential constituent of POMs, but due to the low 

abundance (0.04%) of the nuclide 17 O, it is necessary to enrich such nuclide or 

carry out an 17 O-exchange reaction in 17 O-enriched water in order to obtain a 

good NMR spectrum of POMs. This can lead to problems in the relative 

quantization of the oxygen sites 8 and restricts the application of 17 O NMR 

spectroscopy. 

2.5.2 183 W NMR of Polyoxometalates 

183 W NMR spectroscopy has become a powerful routine method for the 

structural characterization of POMs in solution. 9 The 183 W nuclide is only NMRactive 

isotope in natural tungsten, a transition metal element lying in the sixth 

period, and has a spin of 1/2, so its resonance lines are generally very narrow. 

But its low resonance frequency of 8.325 MHz at 4.7 T and natural abundance of 

57


14.3% result in a low receptivity of 0.059 which makes the observation of 183 W 

signals difficult in many cases. In practice, a concentrated sample solution 

(approx. 1 mol/l) and long acquisition time are necessary. A saturated solution 

of sodium tungstate is recommended as chemical shift reference. The 183 W 

chemical shifts span ca. 8000 ppm and a rough trend is apparent with the 

oxidation states. The higher oxidation state compounds are found at lower field 

and the lower oxidation state compounds are found at higher field. 10 

The following paragraphs are devoted to briefly describe some particularities of 

the 183W NMR spectrum for the Keggin and Eicosatungstodiphosphate 

polyanions, since the novel structures reported in the following chapters of this 

document are based on such polyanions. The reader is recommended to read the 

rich literature on solution studies performed on polyoxometales for a 

comprehensive treatment on the topic. 

2.5.2.1 183 W NMR of the Keggin Structure and their Derivatives 

A Keggin anion [XW 12 O 40 ] (8−n)− (n is the charge of central atom, Figure 2.1) with 

Td symmetry has 12 tungsten atoms which are located in the same chemical and 

magnetic environment, and therefore exhibit a very sharp line with a half-peak 

width less than 1Hz 11 except [PW 12 O 40 ] 3− whose line is split into a narrow doublet 

by coupling between 31 P and 18 3W, 2 J P–O–W ≈ 1 Hz. 

58


Figure 2.1 Polyhedral representation of the [XW 12 O 40 ] (8−n)− Keggin anion (the 

yellow ball represents the central heteroatom X). 

The chemical shifts vary with the central atom, showing the sensitivity of 183 W to 

such atom. Isomerization of the Keggin anion occurs when one or two of the four 

triplets are rotated by 60° around its C 3 axis, forming the β- or γ-isomer, 

respectively. The symmetry of the [XW 12 O 40 ] (8−n)− isomers decreases (see Chapter 

I: 1.2.3.2 Isomeric Forms of the Keggin Heteropolyanion: Baker Figgis Isomers) in the 

sequence of α-isomer (T d ) → β-isomer (C 3v ) → γ-isomer (C 2v ), whereas the number 

of resonance lines increases in the same sequence. 12,13 

Kazansky 14 investigated the correlation of chemical shift with the geometry of 

POMs and the W–O distances and bond angles. He noted that the 183 W NMR 

spectrum shift upfield as the mean bond length of the W–O–W bridge bonds 

decreases. For example the mean distance of the W–O–W bridge bond in 

[XW 12 O 40 ] (8−n)− decreases in the sequence of P V , Si IV , (2H) 2+ and the chemical 

shifts move upfield in the same sequence. 

59


Removal of one WO 4+ group from the Keggin anion produces a monolacunary 

[XW 11 O 39 ] n− anion in which the W atoms divided into six groups, five symmetric 

equivalent pairs of W atoms and a single structurally unique W atom, and 

therefore six lines occur in their 183 W NMR spectra with intensity ratio 2:2:1:2:2:2 

(the order of lines may be vary for individual anion). 11a, 15, 16, 17 Removal of one 

WO 4+ group also results in a broadening of lines and a variety of 2 J W–O–W values. 

Occupation of the vacancy in [XW 11 O 39 ] n− by other metallic atoms, forming socalled 

mono-substituted anions [XMW 11 O 39 ] n− ,does not change the symmetry of 

the anion (C s ) and the spectral envelope. 11b), 18, 19 The resonance lines of 11-W 

species show a general upfield shift except for those W atoms located around the 

vacancy where the increased electronic anisotropy produces a downfield shift. 

Thus, the centre of gravity of the 183 W NMR spectrum remains relatively constant 

for a given heteroatom, and the relative distribution of lines is much the same for 

a homologous series, producing a remarkable similarity in the qualitative 

appearance of the spectra. 20 

Removal of three W atoms from [XW 12 O 40 ] n− produces the trivacant anions 

[XW 9 O 34 ] m- (see Chapter I: 1.2.3.4 Lacunary Species derived from the [α-XM 12 O 40 ] n- 

isomer) The A and B isomers have same C 3v symmetry and should theoretically 

give a two-line spectrum. However, there has been no direct observation of these 

two anionic spectra due to their low solubility and instability in aqueous solution. 

Errington et al. 21 reported the synthesis and 183 W NMR spectrum of a brominated 

polyoxotungstate [A-PW 9 O 26 Br 6 ] 3− . This polyanion exhibit two lines with 

2 J W–O–W = 25 Hz, showing an A-type of tri-vacant anion. Three vacant sites can be 

occupied by other metal atoms, resulting in the so-called three-substituted anion, 

[XM 3 W 9 O 40 ] n− . 

60


When the [XW 9 O 40 ] n− polyanion acts as a ligand, two types of complexes can be 

formed: Keggin sandwich anions M 3 (α-, β-XW 9 O 34 ) 2 (M = Zr, Ce III , Co, Cu, Pd, Sn) 

with C 3h symmetry and M 4 (B-XW 9 O 34 ) 2 (X = P, As; M = Mn, Fe, Co, Ni, Cu, Zn) 

with C 2h symmetry. The former retains the two-line spectrum 22, 23 and the latter 

has a four line spectrum. 24 Recalling from Chapter I, the A- and [B-XW 9 O 34 ] n− 

anions have two isomers, namely α and β. Both isomers of the [A-XW 9 O 34 ] n− have 

the same symmetry and the same two-line spectrum, but the difference of the 

two chemical shifts δ are not identical, in general Δδ(α) > Δδ(β) for [A-XW 9 O 34 ] n− 

and [A-XM 3 W 9 O 40 ] n− , which can be used in distinguishing two isomers. 25 

2.5.2.2 183 W NMR of the monovacant Eicosatungstodiphosphate 

[P 2 W 20 O 70 (H 2 O) 3 ] 10- 

The [P 2 W 20 O 70 (H 2 O) 3 ] 10- ( P 2 W 20 ) polyanion, isolated as a potassium salt, was first 

identified by solution 183 W NMR studies. 26,27,28 It was concluded to be 

structurally between [P 2 W 21 O 71 (H 2 O) 3 ] 6- (P 2 W 21 ) and [P 2 W 19 O 69 (H 2 O)] 14- (P 2 W 19 ), 

containing two [A-α-PW 9 ] halves linked via two W atoms in the equatorial plane 

(see Chapter I: 1.2.5 The Henicosatungstodiphosphate and –arsenate 

[X 2 W 21 O 71 (H 2 O) 3 ] 6- (X = P V , As III ) polyanion and their mono- und dilacunary 

derivatives) as depicted in Figure 2.2. 

61


Figure 2.2 Front view of the monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- (P 2 W 20 ) polyanion 

with a potassium cation in the cavity. The numbers represent the six unique 

tungsten atoms. 

183 W NMR spectra of the aqueous solution of the P 2 W 20 potassium salt consist of 

six signals on the basis of the intensity ratio (1:2:2:2:2:1) at -74.6, -142.4, -159.2, - 

159.6, -103.6 and 195.9 ppm, respectively. Worth to mention that 31 P spectrum 

results in a single peak at -12.3 ppm . According to the spectra, each half of the pa 

contains four different tungsten pairs and a unique tungsten atom in the polar 

cap (W1), with two equivalent belt tungstens (W6) connecting the pa halves 

(Figure 2.2). 28 62


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

MHz for 1 H) magnetic field. The resonance frequencies were 100.580 MHz for 13 C, 

161.923 MHz for 31 P, 149.163 MHz for 119 Sn and 16.666 MHz for 183 W. Chemical shifts 

were given with respect to external standards, namely 1% Si(CH 3 ) 4 in CDCl 3 for 1 H and 

13 C, 85% H 3 PO 4 for 31 P in D 2 O, 5% Sn(CH 3 ) 4 in CDCl 3 for 119 Sn and a 2 M 

Na 2 WO 4·2H 2 O solution in D 2 O for 183 W. All 183 W NMR spectra were collected in 10 

mm probes in highly concentrated solutions, whereas all other nuclei were collected in 

5mm sample tubes. 

2.6 Synthesis of Precursors 

As described in Chapter I, the terminal or “surface” oxygen atoms of a vacant 

polyanion are the most basic ones and correspond to the ideal sites for 

electrophilic attack, therefore, the first step of our investigation consisted in the 

synthesis of vacant polyanions. FT-Infrared spectra were recorded for all 

synthesized precursors and compared with the published literature in order to 

assure their purity. 

2.6.1 Synthesis of Trilacunary Keggin Polyanions 

2.6.1.1 Na 9 [B-α-SbW 9 O 33 ]· 27H 2 O 

Sb 2 O 3 (1.96 g) were dissolved in concentrated HCl (10 mL) and added dropwise 

to a solution of 40 g of Na 2 WO 4·H 2 O in boiling water (80 mL). The mixture was 

refluxed for 60 min. and allowed to cool slowly. Slow evaporation in an open 

beaker resulted in 28.0 g (72% yield) of the desired phase. 29 63


2.6.1.2 Na 9 [B-α-AsW 9 O 33 ]· 27H 2 O 

This lone-pair containing compound was prepared by adding 11 g As 2 O 3 to a hot 

solution of 330 g Na 2 WO 4·H 2 O in 350 mL water. After the addition of 83 mL 11M 

HCl with vigorous stirring over 2 min., the solution was heated at 95°C for 10 

min. and then transferred to a Teflon beaker. The product crystallized overnight 

with a good yield of approx. 90% (280 g). 30 

2.6.1.3 Na 9 [A-α-AsW 9 O 34 ]· 18H 2 O 

To a solution of Na 2 WO 4· 2H 2 O (45 g) in H 2 O (40 mL), 15 mL of 1 M H 3 AsO 4 and 

8.7 mL of pure acetic acid were successively added. The solid which precipitated 

gradually was filtered, washed with ethanol and air-dried with aspiration. 31 

2.6.1.4 Na 9 [A-α-HSiW 9 O 34 ]· 23H 2 O 

Na 2 SiO 3 (11 g) was dissolved in 200 mL of water and 182 g of Na 2 WO 4· 2H 2 O 

was added. 130 mL. of HCl 6M was added into the stirred solution. The solution 

was then boiled for 1 hr. and concentrated to 300 mL. Undissolved material was 

filtered off and a solution of 50 g of anhydrous sodium carbonate in 50 mL of 

water was added. Then the lukewarm solution was gently stirred and the desired 

phase precipitated. 32 

2.6.1.5 Na 9 [A-α-HGeW 9 O 34 ]· 23H 2 O 

Na 2 GeO 3 (12 g) was dissolved in 200 mL of water and 182 g of Na 2 WO 4· 2H 2 O 

was added. 130 mL. of HCl 6M was added into the stirred solution. The solution 

was then boiled for 1 hr. and concentrated to 300 mL. Undissolved material was 

filtered off and a solution of 50 g of anhydrous sodium carbonate in 50 mL of 

water was added. Then the lukewarm solution was gently stirred and the desired 

phase precipitated. 32 64


2.6.1.6 Na 9 [A-α-PW 9 O 34 ]· 7H 2 O 

120 g 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. Afterwards, the pH of the solution was 

measured to be 8.9. Glacial CH 3 COOH was added slowly 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. 33 

2.6.1.7 Na 9 [B-α-BiW 9 O 33 ]· 16H 2 O 

6.5 g of Bi(NO 3 ) 3· 5H 2 O dissolved in 10 ml HCl 6M were added in small portions 

to a hot solution (80 °C) containing 40 g of Na 2 WO 4· 2H 2 O in 80 ml water. The 

mixture was heated at 80 °C for 1 h and then filtered off. The final pH was 7.5. 

After filtration colourless crystals were obtained upon cooling at room 

temperature. Yield: 29 g (74.5%). 34 

2.6.2 Synthesis of Dilacunary Keggin Polyanions 

2.6.2.1 Cs 7 [γ-PW 10 O 36 ] · H 2 O 

75 g of Cs 6 [P 2 W 5 O 23 ] · H 2 O (synthesized according to reference 33) was dissolved 

in 150 g of water and refluxed for 24 hour. The solution was filtered hot through 

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

cooled for 48 hr at approx. 0 °C, and the solid product filtered to recover the 

unconverted Cs 6 [P 2 W 5 O 23 ] · H 2 O, which was again used to synthesize the desired 

phosphorous decatungstate phase. 33 65


2.6.2.2 K 8 [γ-SiW 10 O 36 ]· 20H 2 O 

15 g of the potassium salt of the [β 2 -SiW 11 O 39 ] polyanion are dissolved in 150 mL 

of water at room temperature whereas all undissolved material is removed by 

filtration. The pH of the solution is adjusted to 9.1 by addition of a 2M aqueous 

solution of K 2 CO 3 . The pH of this solution is kept at 9.1 by addition of the 2M 

potassium carbonate solution for exactly 16 minutes. The desired phase is then 

precipitated by addition of 40 g KCl. During the precipitation procedure the pH 

value of the solution must be kept at 9.1 by addition of small amounts of K 2 CO 3 

solution. The solid is removed by filtering, washed with a small amount of 1M 

KCl solution and air dryed. 33 

2.6.2.3 K 8 [γ-GeW 10 O 36 ]· 6H 2 O 

15.2 gr of K 8 [β 2 -GeW 11 O 39 ] · 14H 2 O (synthetic procedure of this monolacunary 

polyanion is described later in this chapter) were dissolved in 150 mL of water. A 

small amount of insoluble material was removed by rapid filtration on a fine frit 

or through Celite ® . The pH of the solution was quickly adjusted to 8.7-8.9 by 

addition of a 2 M aqueous solution of K 2 CO 3 . The pH was kept at this value by 

addition of the K 2 CO 3 solution for exactly 16 min. The product was then 

precipitated by addition of solid KCl (40 g). During the precipitation (10 min), 

the pH was maintained at 8.8 by addition of small amounts of the K 2 CO 3 solution 

or dilute HCl as needed. Then, the solid (yield: 12.4 g, 92%) was filtered off and 

air-dried. 35 66


2.6.3 Synthesis of Monolacunary Keggin Polyanions 

2.6.3.1 K 8 [α-SiW 11 O 39 ]· 13H 2 O 

Solution A: 11 g of sodium metasilicate are dissolved in 100 mL of distilled water 

at room temperature. Undissolved material is filtered off. Solution B: 182 g of 

Na 2 WO 4· 2H 2 O are dissolved in 300 mL of water in a 1 liter beaker. To the boiling 

Solution B, 165 mL of 4M HCl are added dropwise in approx. 30 min. with 

vigorous stirring to dissolve the local precipitate of tungstic acid. Solution A is 

then added and, quickly, 50 mL of 4M HCl are also added, whereas the pH is at 

this point between 5 and 6. The solution is kept boiling for 1 hr. After cooling to 

room temperature, the solution is filtered if it is not completely clear. 150 g of 

KCl are added to the solution under stirring. The white solid product is collected 

on a sintered glass funnel of medium porosity, washed with two 50-mL portions 

of 1M KCl solution and then washed with 50mL of cold water. The desired phase 

is air dried giving an approx. 90% yield (145 g) 33 

2.6.3.2 K 8 [β 2 -GeW 11 O 39 ] · 14H 2 O 

Germanium dioxide (5.4 g) was dissolved in 100 mL of water (solution A). Then, 

182 g of sodium tungstate was dissolved in 300 mL of water in a separate beaker 

(solution B). To this solution, 165 mL of 4 M HCl was added with vigorous 

stirring in small portions over 15 min. Then, solution A was poured into the 

tungstate solution (solution B), and the pH adjusted to between 5.2 and 5.8 by 

addition of 4 M HCl solution (40 mL). This pH was maintained for 100 min by 

addition of the HCl solution. Then, 90 g of solid KCl was added with gentle 

stirring. After 15 min, the precipitate (yield: 112.1 g, 68%) was collected by 

filtration on a sintered glass filter. 35 67


2.6.3.3 K 7 [α-PW 11 O 39 ] · 14H 2 O 

To a solution of 181.5 g of Na 2 WO 4· 2H 2 O in 300 mL water, 50 mL of 1M H 3 PO 4 

and 88 mL glacial acetic acid were added. The resulting solution was refluxed for 

1 hr. and then cooled to room temperature. Addition of 60 g KCl resulted in a 

white precipitate which was collected after 10 min. of continuous stirring and 

after filtration left to air drying. 36 

2.6.4 Synthesis of Mono- Di- and Hexavacant Wells-Dawson Polyanions 

2.6.4.1 K 10 [α 2 -P 2 W 17 O 61 ]· 20H 2 O 

In a 1 liter beaker a sample of 80 g of K 6 [α- or β- P 2 W 18 O 62 ]· xH 2 O (syntesized 

according to reference 33) is dissolved in 200 mL of water, and a solution of 20 g 

of potassium hydrogen carbonate in 200 mL water is added while stirring. After 

1 hr., the reaction is complete, and then the precipitate is filtered on a coarse 

sintered glass frit, dried under suction, and then redissolved in 500 mL of hot 

water (95 °C). The snowlike crystals that appear on cooling to ambient 

temperature are filtered after 3 hours, dried under suction for 5 hrs. and air dried 

for 2 to 3 days. 33 

2.6.4.2 Na 12 [α-P 2 W 15 O 56 ]· 24H 2 O 

In a 600 mL. beaker a sample of 38.5 g of K 6 [α-P 2 W 18 O 62 ]· 14H 2 O is dissolved in 

125 mL of water, and 35 g of NaClO 4· H 2 O are added. After vigorous stirring for 

20 minutes, the mixture is cooled on an ice bath, and the potassium perchlorate is 

removed by filtering after approx. 3 hrs. A solution of 10.6 g of Na 2 CO 3 in 100 

mL of water is added to the filtrate. A fine white precipitate appears almost 

instantaneously and is decanted and then filtered on a medium porosity sintered 

68


glass frit and dried under suction for ~ 3 hrs. The precipitate is then washed for 1 

to 2 minutes with a solution of 4 g of NaCl in 25 mL of water, dried under 

suction for approx. 3 hours, washed for 2 to 3 min. with 25 mL of ethanol, and air 

dried under suction for 3 hrs., washed again with EtOH and dried under suction, 

and finally air dried for 3 days (yield: 22 gr, 62%). 33 

2.6.4.3 K 12 [α-H 2 P 2 W 12 O 48 ]· 24H 2 O 

In a 1 liter beaker a sample of 83 g of K 6 [α- or β- P 2 W 18 O 62 ]· xH 2 O (synthesized 

according to reference 33) is dissolved in 300 mL of water, and a solution of 48.4 

g of tris(hydroxymethyl)aminomethane in 200 mL of water is added. The 

solution is left at room temperature for 30 min. and then 80 g of potassium 

chloride are added. After complete dissolution, a solution of 55.3 g of K 2 CO 3 in 

200 mL of water is added. The solution is vigorously stirred for approx. 15 min., 

and the white precipitate that appears after a few minutes is filtered on a coarse 

sintered glass frit, dried under suction for 12 hrs., washed with 50 mL of ethanol 

for 2 to 3 minutes and dried under suction for another 3 hrs., washed again with 

EtOH and dried under suction, and finally air dried for 3 days. 60 grs. of the 

desired phase were obtained (89% yield). 33 69


2.6.5 Synthesis of further Polyoxotungstophosphate Species: The 

Monovacant Eicosatungstodiphosphate, Divacant 

Nonadecatungstodiphospate and Octatetracontatungstooctaphosphate 

Polyanions. 

2.6.5.1 K 14 [P 2 W 19 O 69 (H 2 O)]· xH 2 O 

A solution of 10.65 g of Na 9 [A-α-PW 9 O 34 ]· 7H 2 O in 50 mL of water was added to 

a solution of 4.0 g of K 7 [α-PW 11 O 39 ] · 14H 2 O in 50 mL of water. The pH is 

measured to be between 6.0 and 6.5 and the mixture is stirred for 30 minutes at 

50 °C. Solid KCl is added slowly until a fine crystalline precipitate appeared. 

Further 3.5 g potassium chloride was then added and a crystalline powder 

separated and stirring is maintained until room temperature is reached. The 

product is filtered and washed with 10 mL of chilled water, the desired phase is 

afterwards air dried for two days. 27 

2.6.5.2 K 10 [P 2 W 20 O 69 K(H 2 O) 2 ]· 24H 2 O 

100 mL of a 1M Na 2 WO 4· 2H 2 O solution and 10 mL H 3 PO 4 1M are slowly 

acidified with 51 mL of a 3M HCl solution. The white precipitate that 

immediately appears is reddisolved by ebullition. The solution is left to cooldown 

to room temperature (previously filtrated while hot if not all the solid 

material redissolved by ebullition) and the crystalline material that appears after 

1 or 2 days is redissolved in a minimum amount of water. 36 70


2.6.5.3 K 28 Li 5 H 7 [P 8 W 48 O 184 ]· 92H 2 O 

In 950 mL of water are dissolved, successively, 60 g of glacial acetic acid, 21 g of 

lithium chloride, and 28 g of K 12 [α-H 2 P 2 W 12 O 48 ]· 24H 2 O. The solution is left in a 

closed flask. After 1 day, white needles appear and crystallization continues for 

several days. After 7 days the crystals are collected by suction on a coarse frit and 

air dried for 3 days. Yield: 9 g (34%). 33 

2.6.6 Synthesis of further Polyoxotungstoarsenate Species: The 

Monovacant Eicosatungstodiarsenate and the 

Tetracontatungstotetraarsenate (III) Polyanions 

2.6.6.1 K 14 [As 2 W 19 O 67 (H 2 O)]· xH 2 O 

The title compound was synthesized by addition of 0.89 g of As 2 O 3 , 18.8 g of 

Na 2 WO 4· 2H 2 O and 0.67 g KCl to 50 mL H 2 O at 80°C with stirring. After 

dissolution the pH was adjusted to 6.3 by adding 12M HCl dropwise. The 

solution was kept at 80°C for 10 min and then filtered. Finally 15 g KCl was 

added and the solution stirred for 15 minutes. The white precipitate formed was 

isolated by filtration and dried at 80°C resulting in 15.4 g product (95% yield). 37 71


2.6.6.2 Na 27 [NaAs 4 W 40 O 140 ]· 60H 2 O 

132 g of Na 2 WO 4· 2H 2 O and 5.2 g of sodium meta arsenite (NaAsO 2 ) are 

dissolved in 200 mL of distilled water at 80 °C. 82 mL of a 6 M HCl solution is 

added slowly with vigorous stirring. The final pH is approx. 4.0. The container is 

placed in a refrigerator just above 0 °C whereas the solid starts to slowly 

crystallize. After one day the deposited solid is collected on a filter and air dried. 

Yield: 80 g (69%). 33 72



(1) Pope, M. T. Heteropoly and Isopoly Oxometalates; Springer-Verlag: Berlin, 

Germany, 1983. 

(2) Moffat, J. B. Metal-Oxygen Clusters. The Surface and catalytic properties of 

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76





3.1 Introduction 

In the present work, a series of novel iso- and heteropolytungstates functionalized by 

mono- and diorganotin groups will be reported, whereas for most of the cases presented 

vacant polyoxoanions were used in order to graft the organotin function in the lacuna, 

and only the novel [{Sn(C 2 H 5 ) 2 } 2 (W 6 O 22 )] 4- one-dimensional diethyltin isohexatungstate 

chain (this compound will be treated in detail later in this work) has the diorgano groups 

grafted at the surface of the polyanion. 

The systematic functionalization of polyoxometalates (POMs) can lead to 

assemblies with novel structures and may allow for a rational design of tailored 

catalytic systems, an increase of the selectivity to specific targets, or other 

unexpected synergistic effects. Substituted polyanions are also interesting 

building blocks for crystal engineering because they can establish a variety of 

networks of intermolecular interactions so that their properties and applications 

could be influenced. It is known that the size, shape and charge density of many 

polyoxoanions are of interest for pharmaceutical applications (e.g. antiviral, 

antitumor). 1 However, the mechanism of action of many polyoxoanions is not 

selective towards a specific target. In order to improve selectivity it often appears 

desirable to modify a given polyoxoanion core structure slightly, nonetheless, 

such attempts result frequently 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. 

77



It has been proved, that modification of the POM framework with covalently 

attached organometallic units results in hybrid POMs with organic 

functionalities. 

1g(Part II, Functionalized Polyoxometalates) 

Interaction of organotin groups (R 2 Sn 2+ ) as electophiles towards POMs have been 

studied since the late 1970´s until now resulting in numerous novel compounds 

with unprecedented architectures, from monomeric to dodecameric species and 

also extended materials with dimensionalities ranging from 1 to 3. 2-7 The Sn-C 

bond has shown to be hydrolytically stable in water at a wide pH range, also 

Sn(IV) can substitute W(VI) in polyoxometalates (POMs) skeletons (i.e. in vacant 

polyanions) making then the RSn 3+ and R 2 Sn 2+ excellent candidates for 

functionalization of POMs resulting in a hybrid organic-inorganic species. 

The so-called “surface” oxygen atoms in the vacant polyoxoanions have a very 

strong basic nature, hence such atoms represent the ideal coordination site for 

electrophilic attack, i.e. RSn 3+ and R 2 Sn 2+ groups, whereas the organotin group, 

with its Lewis-acid character fits well in the lacuna of the basic sites of the POM. 

Nevertheless, the reaction mechanisms are at this point very little understood 

and it is best described as a “self-assembly” process. Therefore the synthesis of 

new hybrid organic-inorganic polyanions (as well as the complete structural 

characterization of known species) remains an important research objective. 

It has been observed from the numerous organotin derivatives synthesized over 

the past few decades (see references 2 to 7), that RSn 3+ and R 2 Sn 2+ groups 

attached to POMs frameworks are normally five or six coordinated (trigonal 

bypiramidal or octahedral geometry, respectively) fact that fits quite well in the 

cases where the organotin moiety substitutes addenda metal centres in POM 

skeletons, i.e. WO 6 . Primarily, two aspects of organotin chemistry account for the 

78



increase of coordination number 4 to 5 or 6, namely the association of organotin 

halides R n SnX 4-n by means of 

bridges and the ease of formation of 

stannoium ions [R n Sn(H 2 O)] (4-n)+ through ionization in donor solvents. 8 

3.2 General Experimental Procedure for the Functionalization of 

Polyoxotungstates with Organotin Groups 

For the present research work on organotin functionalized polyoxotungstates, 

dimethyl- and diethyltindichloride were used as sources of the R 2 Sn 2+ 

electrophiles. Me 2 SnCl 2 as well as Et 2 SnCl 2 have a structure in the solid state 

consisting of a one-dimensional polymer with chlorine bridges whit Sn-Cl 

distances a 2.4 and b 3.54 Å, and Me-Sn-Me angle of 123.5° (Figure 3.1). 9 

X 

X 

R 

Sn 

R 

a 

b 

X 

X 

b 

a 

R 

R 

Sn 

X 

X 

R 

Sn 

R 

X 

X 

Figure 3.1 Polymeric Structure of Me 2 SnCl 2 and Et 2 SnCl 2 in the solid state. 

In general, distilled water was used as the common solvent, unless otherwise 

specified, i.e. all experiments were conducted in open air since stability of the 

potential novel compounds at normal atmospheric conditions (humidity and 

presence of oxygen) needed to be tested from the beginning. Organotin chlorides 

were used as purchased without further purification and the polyoxotungstates 

precursors were synthesized following published literature as described in 

Chapter II. In order to obtain suitable crystalline material for every experiment 

79



performed, common alkaline, ammonium or guanidinium salts either in solution 

(0.2 to 1 moles/L) or pure as solid were used at the end of the experiment aiming 

to the precipitation of the heteropolysalt, normally by slow evaporation, vapour 

diffusion or by addition of small amounts of organic solvents to the aqueous 

solution. 

The following paragraphs are devoted to describe a general overview of the experimental 

procedure followed for the synthesis of organotin functionalized polyoxotungstates, 

whereas the detailed experimental procedure for each compound will be explained in 

detail in the following chapters dedicated to each compound. 

Several factors need to be taken into consideration regarding the synthesis of 

new species, namely the molecular ratio of reactants, temperature, final pH value, 

nature of the solvent and nature of the counter-ions are the most important ones. 

When a novel compound was found, the above mentioned factors were finetuned 

in order to obtain the given compound at the highest yield possible 

without impurities or mixture of species. 

80



A general experimental procedure is described for the reaction of the R n Sn (4-n)+ 

group towards a polyanion, namely: 

1. Stoichiometric amounts (with approx. 10% excess) of the diorganotindichloride 

were added to 20 to 30 mL distilled water until dissolution completed. 

diorganotin halides experiment the following hydrolytic sequence in the 

presence of water: 10 

H 2 O 

H 2 O 

R 2 SnCl 2 R 2 Sn(Cl)OH ClR 2 SnOSnR 2 Cl 

H 2 O 

H 2 O 

H 2 O 

(R 2 SnO) n HOR 2 SnOSnR 2 OH HOR 2 SnOSnR 2 Cl 

Scheme 3.1 Hydrolytic Sequence of Diorganotindichloride Species 

As shown above, hydrolysis of diorganotin chlorides result first in 

tertraorganodichlorodistannoxanes, ClR 2 SnOSnR 2 Cl, then the chloridehydroxides 

HOR 2 SnOSnR 2 Cl, and ultimately the polymeric oxides (R 2 SnO) n . It is 

worth to note that the Sn-C bond survives quite well the hydrolysis. The R 

groups in the polymeric oxides (R 2 SnO) n are usually trans to each other and form 

five- or six-coordinate complexes where further substitution of the oxo groups 

takes place by means of nucleophilic substitution. In general, the Lewis acid 

strength of the organotin halides R n SnX 4-n decrease as n increases. 11 On the other 

hand, for the polymeric diorganotin oxides the polarity of the Sn δ +-O δ - bond 

enhances the Lewis acidity of the tin. 12 81



Aqua complexes of R 2 Sn 2+ have been studied in aqueous solutions whereas 

octahedral R 2 Sn(OH 2 ) 4 

2+ (R = Me, n-Bu) have been identified 

crystallographically. 13 

2. Stoichiometric amounts of the lacunary polyoxotungstate/ sodium tungstate 

were added to the solution described in step 1. 

3. After complete dissolution (sometimes this is not achieved until heating is 

applied or acidification performed), the pH of the mixture was measured and 

adjusted if necessary to the desired value by adding aqueous solutions of 

inorganic acids and/or bases at different concentrations. 

4. When the pH of the reaction mixture was adjusted, stirring either at room 

temperature or at higher temperature (up to ebullition) for time that varied from 

10 minutes to several hours/days. 

5. After the reaction time was reached, the lukewarm solution was filtered (if the 

reaction was conducted at temperatures > 50 °C) in order to separate all 

unreacted material. 

6. The filtered solution was transported to one or several scintillation vials or 

beakers, whereas either solid or solutions of alkali, ammonium or guanidinium 

salts were added in order to bulk precipitate the iso- or heteropolysalt. 

7. In order to obtain crystallized product suitable for single crystal X-ray 

measurements, a small amounts of solutions of alkali, ammonium or 

guanidinium salts were added to the filtered solutions and leave for slow 

evaporation. 

82



3.3 General Characterization Procedure for Polyoxotungstates 

Functionalized with Organotin Groups 

After completion of a reaction, the next objective is to find out if the product 

represents a novel species. Providing that material precipitate after the 

crystallization procedure (slow evaporation, vapour diffusion, etc.) a very quick 

method to identify if the resulting compound has indeed the organotin moiety 

grafted to the POM framework consists in performing a FT-Infrared 

measurement. A series of bands below 1100 cm -1 reveals the presence of the 

polyoxotungstate skeleton, whereas the Sn-C different vibration modes as well as 

the organic C-H signals would be expected between 1800 and 1100 cm -1 (a 

detailed treatment of the infrared interpretation will be described for each 

compound in the following sections). 14-16 

Crystallographic studies by means of single X-ray diffraction reveals the bonding 

nature and the configuration of the atoms in a compound, as well as other 

important information not possible to obtain by other methods, therefore special 

efforts are devoted to obtain adequate crystalline material after the infrared 

measurements already gave hints of the presence of the desired components in 

the reaction product (organotin moiety + polyoxotungstate framework). 

On condition that the crystallographic studies resulted in enough information on 

the nature of the compound in the solid state and after performing a thoroughly 

search in crystallographic databases 17 in order to confirm that the measured 

species constitute a novel, i. e. not reported one, further characterization 

techniques follow, namely thermogravimetric studies in order to reveal the 

thermal stability of the compound to acquire information on its hydration state 

83



(thermogravimetric analysis and elemental analysis are complementary 

techniques in order to provide accurate information on the elements/groups 

present in the bulk solid). 

At this stage, the characterization in the solid state for the novel species is 

completed, therefore further investigations in solution follow. Multinuclear 

Nuclear Magnetic resonance is a very powerful technique that applies quite well 

to the compounds treated here, since there are several NMR active nuclei prone 

to be studied with this method, namely 1 H, 13 C, 31 P, 119 Sn and 183 W. On the other 

hand, most of the reported compounds in this work were not soluble enough to 

perform NMR measurements and even ion exchange try-outs or addition of 

LiClO 4 to the aqueous solution of the less soluble compounds did not delivered 

good quality spectra. Efforts to solubilise compounds insoluble in aqueous media 

with organic solvents failed or resulted in low quality spectra. 

The final step in the characterization of a novel species consisted in the finetuning 

of the experimental procedure in order to obtain a higher yield and to 

improve their purity. 

84




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88

Chapter IV. 3-D Assemblies of Mono- and Diorganotin Functionalized Heteropolytungstates 

Chapter IV. 3-D Assemblies of Mono- and Diorganotin 


As for now, a novel polyanion will be described with a sequential number, whereas when 

referring to its salt, one or two letters (i.e. counter-cation) will be placed before the 

number, e. g. polyanion 1: [{(CH 3 ) 2 Sn(H 2 O)} 3 (A-α-PW 9 O 34 )] 3- , while its guanidinium 

salt, including hydration molecules will be illustrated as G-1: 

[C(NH 2 ) 3 ] 3 [{(CH 3 ) 2 Sn(H 2 O)} 3 (A-α-PW 9 O 34 )]· 9H 2 O 

4.1 3-D Assemblies of Dimethyltin Functionalized [A-α-XW9O34] n- 

(X = P V , As V , Si IV ) Keggin polytungstates 

A series of novel 3-D assemblies in the solid state will be reported, namely the 

isostructural 

([C(NH 2 ) 3 ] 2 Na[{(CH 3 ) 2 Sn(H 2 O)} 3 (A-α-AsW 9 O 34 )]· 8H 2 O) ∞ (GNa-1) 

([C(NH 2 ) 3 ] 2 Na[{(CH 3 ) 2 Sn(H 2 O)} 3 (A-α-PW 9 O 34 )]· 9H 2 O) ∞ 

(GNa-2) and 

([C(NH 2 ) 3 ] 2 Na[{(CH 3 ) 2 Sn(H 2 O)} 3 (A-α-SiW 9 O 34 )]· 10H 2 O) ∞ (GNa-3) compounds. 

Reaction of the (CH 3 ) 2 Sn 2+ electrophile toward trilacunary [A-α-XW 9 O 34 ] n- Keggin 

polytungstates (X = P V , As V , Si IV ) with guanidinium as templating-cation resulted 

in the isostructural compounds, constituting the first 3-dimensional assemblies of 

organotin-functionalized polyanions, as well as the first example of a 

dimethyltin-containing tungstosilicate in the case of GNa-3, and showing a 

similar chiral architecture based on tetrahedrally-arranged {(CH 3 ) 2 Sn} 3 (A-α- 

XW 9 O 34 ) monomeric building-blocks connected via intermolecular Sn-O=W 

bridges regardless of the size/charge of the heteroatom. 

89


4.1.1 Synthetic Procedure 

To a solution of (CH 3 ) 2 SnCl 2 (~0.6 mmol) in water (20 mL) solid Na y [A-α- 

XW 9 O 34 ]·nH 2 O (~0.2 mmol), (X = P V , As V , Si IV )was added and the pH of the 

resulting solution was adjusted between 2 and 3 with aqueous 1M HCl. After 

heating at 80°C for 30 minutes, the solution was cooled to room temperature and 

aqueous 1M [C(NH 2 ) 3 ]Cl (0.5 mL) was added. Colorless, tetrahedral singlecrystals 

suitable for X-ray diffraction were obtained after approximately 10 - 15 

days by slow evaporation at room temperature. Exact amounts used for each 

compound are described below: 

Compound (GNa-1). 0.127 g of (CH 3 ) 2 SnCl 2 (0.579 mmol) and 0.500 g of Na 9 [A-α- 

AsW 9 O 34 ]·11H 2 O (0.187 mmol) were used and the pH was adjusted to 3. Yield: 

0.29 g, 51% based on W. IR ν max /cm -1 : 1200(w), 983(sh), 953(s), 862(s), 841(s), 

758(vs), 700(vs), 584(sh), 515(mw), 483(m), and 412(m). 

Compound (GNa-2). 0.133 g of (CH 3 ) 2 SnCl 2 (0.605 mmol) and 0.500 g of Na 9 [A-α- 

PW 9 O 34 ]·7H 2 O (0.195 mmol) were used and the pH was adjusted to 2. Yield: 0.14 

g, 23% based on W. IR ν max /cm -1 : 1200(w), 1077(s), 1018(m), 948(s), 918(s), 897(m), 

836(s), 765(vs), 716(vs), 597(m), 575(m) and 516(m). 

Compound (GNa-3). 0.122 g of (CH 3 ) 2 SnCl 2 (0.557 mmol) and 0.500 g of Na 10 [Aα-SiW 

9 O 34 ]·18H 2 O (0.180 mmol) were used and the pH was adjusted to 2. Yield: 

0.25 gr, 45% based on W. IR ν max /cm -1 : 1200(w), 1002(m), 945(s), 887(vs), 843(s), 

754(vs), 709(vs), 558(m) and 512(m). 

90


4.1.2 FT-Infrared Spectroscopy 

The IR spectra of GNa-1, GNa-2 and GNa-3 show similar overall shapes, which 

are reminiscent of the polyoxometalate precursors with significant changes in 

some band positions, indicating functionalization of the POMs with retention of 

the (A-α-XW 9 O 34 ) fragments (Figure 4.1). 

The region below 1000 cm -1 displays a strong peak at 945 - 955 cm -1 

corresponding to the stretching asymmetric (ν as ) (W=O t ) vibration, at least one 

strong signal in the range 860 - 920 cm -1 attributed to the ν as (W-O t ) + ν as (X-O) 

combination, two very strong bands at ~760 and 710 cm -1 originating from the 

ν as (W-O-W) vibration, and several medium peaks below 600 cm -1 assigned to 

δ(O-X-O) / δ(W-O-W) vibrations. 1 

The bands above 1000 cm -1 observed for GNa-2 (1077, 1018 cm -1 ) and GNa-3 

(1002 cm -1 ) are related to the ν as (X-O) mode and the (CH 3 ) 2 Sn 2+ moieties are 

unequivocally identified in all three compounds by weak peaks at 1200 cm -1 

assigned to the bending symmetric (δ s ) vibration of CH 3 in methyltin 

derivatives. 2 91


Figure 4.1 FT-Infrared Spectra of compounds GNa-1 (red), GNa-2 (blue) 

and GNa-3 (green). 

92


4.1.3 Thermogravimetry 

Thermal decomposition for GNa-1, GNa-2 and GNa-3 (Figures 4.2, 4.3 and 4.4) 

starts with a dehydration step at 185 – 200 ºC [calc (found): GNa-1, 6.40% (6.39%); 

GNa-1, 7.04% (7.25%) GNa-3, 7.44% (7.59%)], immediately followed by a single 

or two highly overlapping mass loss steps involving the release of the [C(NH 2 ) 3 ] + 

cations together with the loss of the methyl groups below 435 – 455 ºC. 

Figure 4.2 Thermogram of compound GNa-1. 

93




94


4.1.4 Single Crystal X-ray Diffraction 

Single-crystal XRD reveals that GNa-1, GNa-2 and GNa-3 are isostructural and 

they crystallize in the chiral P2 1 3 cubic space group with four {(CH 3 ) 2 Sn} 3 (A-α- 

XW 9 O 34 ) monomeric building-blocks in the unit cell, each of them with C 3v 

symmetry, provided that the methyl groups can freely rotate. These monomeric 

units are composed of three (CH 3 ) 2 Sn 2+ groups anchored via two Sn-O(W) bonds 

each on the vacant sites of a (A-α-XW 9 O 34 ) fragment (Figure 4.5), which is 

derived from the parent [α-XW 12 O 40 ] Keggin cluster by removal of three cornersharing 

WO 6 octahedra (see Chapter I: 1.2.3.4 Lacunary Species derived from the [α- 

XM 12 O 40 ] n- isomer). The coordination environment around the Sn centers is 

distorted octahedral trans-(CH 3 ) 2 SnO 4 , with the axial positions occupied by the 

methyl groups in a relative trans arrangement, and the equatorial plane defined 

by terminal O atoms of an edge-shared {W 2 O 10 } dimer (O1S, O2S), one 

coordination water molecule (O1Sn), and one terminal O atom belonging to the 

{W 6 O 27 } belt of a neighboring monomeric unit (O2T i ). Bond valence sum (BVS) 

calculations 3 confirm diprotonation of the O1Sn atom. Bond lengths and angles 

are similar to other polytungstates containing trans-(CH 3 ) 2 SnO 4 moieties, 4 with 

the equatorial bonding defined as two short, one long and one very long bonds 

and the C-Sn-C significantly deviated from linearity (see Table 4.1). 

95



{(CH 3 ) 2 Sn} 3 (A-α-XW 9 O 34 ) monomeric building-block in 1 – 3. Color code: WO 6 

octahedra: teal; X: yellow [X = As V (1), P V (2), Si IV (3)]; C: black; O: red; Sn: olive 

green; H: light grey. 

Table 4.1 Selected Bond Lengths (Å) and Angles (°) of Polyanions 1, 2 and 3. 

1 2 3 

Sn-O1S 2.111(16) 2.078(11) 2.115(14) 

Sn-O2S 2.173(17) 2.154(11) 2.143(13) 

Sn-O1Sn 2.34(2) 2.325(12) 2.324(18) 

Sn-O2T 2.409(16) 2.483(11) 2.396(15) 

Sn-C1 2.12(3) 2.114(16) 2.15(2) 

Sn-C2 2.08(3) 2.072(18) 2.09(2) 

C1-Sn-C2 163.9(11) 159.1(7) 161.1(9) 

96


The four monomeric building-blocks in the unit cell are arranged with the 

heteroatoms occupying the vertexes of a tetrahedron, in such a way that one 

of them is linked to the other three by its three (CH 3 ) 2 SnO 4 moieties (green [Aα-XW 

9 O 34 ] unit in Figure 4.6), and more specifically, through equatorial 

coordination of the Sn centers to the terminal O2T i atoms. The center of this 

tetrahedron is occupied by a [C(NH 2 ) 3 ] + cation placed almost parallely over 

the plane defined by the internal methyl groups, with short C Me···N distances 

around 3.5 Å. As a result of its rigid triangular geometry, the [C(NH 2 ) 3 ] + 

cation stabilizes this POM arrangement by holding together the latter three 

monomers via formation of a multitude of strong N-H···O POM hydrogen 

contacts (Figure 4.6). 

Figure 4.6 Guanidinium templated tetrahedral arrangement of monomers in 

the unit cell. Color code is the same as in Figure 4.5. Central (A-α-XW 9 O 34 ) unit 

illustrated in green for clarity. 

97


In addition, the first mentioned monomeric building-block is as well 

connected to other three from adjacent cells via coordination of terminal O 

atoms from the tungsten belt to form W2=O2T-Sn ii bridges (Figure 4.7). This 

pattern results in a 3-dimensional hybrid organic-inorganic POM assembly 

where each {(CH 3 ) 2 Sn} 3 (A-α-XW 9 O 34 ) monomeric unit is linked to the six 

nearest neighbours. This type of assembly displays chirality, and we observed 

a clockwise orientation of the monomeric units in 1 and 2, whereas the anticlockwise 

orientation was found for 3. 

Figure 4.7 Detail of the connectivity of a {(CH 3 ) 2 Sn} 3 (A-α-XW 9 O 34 ) monomeric 

building block (center) with monomers from adjacent unit cells. 

98


Table 4.2. Crystallographic Data of Compounds GNa-1, GNa-2 and GNa-3. 

GNa-1 GNa-2 GNa-3 

Formula C 8 H 52 AsN 6 NaO 45 Sn 3 W 9 C 8 H 54 N 6 NaO 46 PSn 3 W 9 C 8 H 56 N 6 Na 2 O 47 SiSn 3 W 9 

Mol. Wt. 

(g/mol) 

3061.11 3035.18 3073.30 

Crystal colour colourless colourless colourless 

Crystal size 

(mm) 

0.17 x 0.17 x 0.09 0.33 x 0.18 x 0.12 0.34 x 0.34 x 0.21 

Crystal system cubic cubic cubic 

Space group 

(Nr.) 

198 198 198 

a (Ǻ) 17.6040(9) 17.5942(3) 17.5199(4) 

Volume (Ǻ 3 ) 5455.5(5) 5446.39(16) 5377.7(2) 

Z 4 4 4 

D calcd (g/cm 3 ) 3.772 3.532 3.888 

Abs. coeff. μ 

(mm -1 ) 

Total Reflections 

measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

20.950 20.397 20.675 

75800 50041 53126 

2850 3760 4176 

2122 3236 3342 

0.0468 0.0403 0.0518 

0.1163 0.0944 0.1466 

GoF 0.998 1.057 1.076 

a R(F) = Σ||F o | - |F c ||/Σ|F o |; wR(F 2 ) = {Σ[w(F o 

2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

99


4.2 3-D Assembly of an Ethyltin Functionalized [A-α-AsW9O34] 9- 

Keggin polyoxotungstate 

Reaction of the (C 2 H 5 ) 2 Sn 2+ electrophile toward the trilacunary [A-α-AsW 9 O 34 ] 9- 

Keggin polyanion with guanidinium as templating-cation resulted in the first 3- 

dimensional assembly of ethyltin functionalized polyoxotungstoarsenate: 

([C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 )]· 5H 2 O) ∞ (G-4) 

Polyanion 4 is isostructural with the ones reported previously in this Chapter (4.1 

Assemblies of Dimethyltin Functionalized [A-α-XW 9 O 34 ] n- (X = P V , As V , Si IV ) Keggin 

polytungstates). The monomeric {Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 ) building 

unit is chiral and is connected to other units via intermolecular Sn-O=W bridges. 

Nevertheless, (C 2 H 5 ) 2 Sn 2+ suffered partial hydrolysis whereas one ethyl group is 

lost as found by X-ray crystallography. 


0.076 g (0.3051 mmol) of (C 2 H 5 ) 2 SnCl 2 were added to a beaker with 25 mL water 

until dissolution, afterwards 0.25 g (0.1017 mmol) of Na 9 [A-α-AsW 9 O 34 ]· 18H 2 O 

were added and the pH of the resulting solution was adjusted to 3 with aqueous 

HCl 1M. After heating at 40 °C for 60 minutes, the solution was filtered to 

separate the unreacted material and to the lukewarm solution 0.5 mL of 

[C(NH 2 ) 3 ]Cl 1M was added. Colourless, tetrahedral single-crystals suitable for X- 

ray diffraction were obtained after approximately 7 days by slow evaporation at 

room temperature. Yield: 0.13 g, 43% based on W. IR ν max /cm -1 : 1453(w), 1418(w), 

1379(w), 1229(w), 1192(m), 950(s), 856(w), 828(w), 782(w), 742(w), 679(m), 518(w), 

484(w). 

100



The IR spectra of G-4 (Figure 4.8) point out the presence of the (A-α-AsW 9 O 34 ) 

unit, with noteworthy changes in some band positions, indicating 

functionalization of the polyoxotungstoarsenate, as the bands below 1000 cm -1 

illustrate. The peak at 950 cm -1 corresponds to the W=O t stretching asymmetric 

vibration (v as ) whereas the signals between 860 and 670 cm -1 are attributed to the 

stretching W-O-W bridges between corner-sharing and edge-sharing WO6 

octahedra [compare the spectra of G-1, which is also based on the trilacunary (Aα-AsW 

9 O 34 ) polyanion]. The presence of the diethyltin group attached to the (Aα-AsW 

9 O 34 ) unit is unambiguously established by the occurrence of two peaks of 

low and medium intensity at 1230 and 1193 cm -1 respectively, characteristic of 

the bending symmetric vibration (δ sy ) of organotin derivatives. 2 Additionally, 

three signals of medium intensity between 1450 and 1370 cm -1 corresponds to δ sy 

and δ as of the CH 3 group, and δ sy CH 2 , respectively. 5 

Figure 4.8 FT-Infrared Spectrum of compound G-4. 

101



In Figure 4.9 is illustrated the thermogravimetric analysis performed on G-4, 

where four lucid decomposition steps takes place. First, a dehydration step 

between 127 and 181 °C results in the loss of eight water molecules and the three 

monoprotonated oxygen atoms attached to the Sn [calc (found): G-4, 6.36 (6.33)], 

directly followed by the loss of the [C(NH 2 ) 3 ] + cations simultaneously with the 

ethyl groups below 450 °C. 

Figure 4.9 Thermogram of compound G-4. 

102



Compound G-4 crystallize in the chiral P2 1 3 cubic space group with four 

[{Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 )] monomeric building-blocks in the unit 

cell. Assuming free rotation of the ethyl group, the monomeric unit has C 3v 

symmetry. The 3-dimensional arrangement is equivalent to that of compounds 

G-1, G-2 and G-3 treated previously in this chapter; whereas the main difference 

consists in the loss of one ethyl group that is substituted by a monoprotonated 

oxygen (O2SN) atom in a position trans relative to the ethyl group (Figure 4.10). 


{Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 )]monomeric building-block in 4. Color 

code: WO 6 octahedra: sea green; As V : yellow; C: black; O: red; Sn: olive green; H: 

light grey. 

103


These monomeric units are composed of three (C 2 H 5 ) 2 Sn 2+ groups anchored via 

two Sn-O(W) bonds each on the vacant sites of a (A-α-AsW 9 O 34 ) fragment, which 

is derived from the parent [α-XW 12 O 40 ] Keggin cluster by removal of three 

corner-sharing WO 6 octahedra (see Chapter I: 1.2.3.4 Lacunary Species derived from 

the [α-XM 12 O 40 ] n- isomer). The coordination environment around the Sn centers is 

distorted octahedral trans-(C 2 H 5 )SnO 5 , with the axial positions occupied by an 

ethyl group and a monoprotonated oxygen atom (as confirmed by BVS 

calculations 3 ) in a relative trans arrangement, and the equatorial plane defined by 

terminal oxygen atoms of an edge-shared {W 2 O 10 } dimer (O1A, O2WS), one 

coordination water molecule (O1SN), and one terminal O atom belonging to the 

{W 6 O 27 } belt of a neighboring monomeric unit (O2T i ). 

Table 4.3 portrays the distances of the atoms connected to the central tin in the 

environment of the (C 2 H 5 )SnO 5 , octahedron, as well as the angle between the 

ethyl group and the oxygen in its relative trans position. 

Table 4.3 Selected Bond Lengths (Å) and Angles (°) of Polyanion 4. 

4 

Sn-O1A 2.09(2) 

Sn-O2WS 2.17(2) 

Sn-O2Sn 2.09(3) 

Sn-O1Sn 2.42(3) 

Sn-O2T 2.45(2) 

Sn-C1 2.14(3) 

C1-Sn-O2Sn 156.5(12) 

104


Comparing the values from Table 4.3 with those reported for the isostructural 

compounds with dimethyltin (Table 4.1), results evident that the distances 

between tin and the terminal oxygen atoms of an edge-shared {W 2 O 10 } dimer 

(O1A, O2WS) as well as the Sn-C length are quite similar, whereas the other Sn-O 

are slightly larger, meanwhile the angle between C1-Sn-O2SN is approx. 7° 

smaller. 

Very similar to polyanions 1, 2 and 3; the four monomeric building-blocks in 

the unit cell are arranged with the heteroatoms (As V ) occupying the vertexes 

of a tetrahedron, in such a way that one of them is linked to the other three by 

its three (C 2 H 5 )SnO 5 moieties (teal [A-α-AsW 9 O 34 ] unit in Figure 4.11), and 

more specifically, through equatorial coordination of the Sn centers to the 

terminal O2T i atoms. Exactly like in the case of polyanions 1 - 3, the 

[C(NH 2 ) 3 ] + cation stabilizes this POM arrangement by holding together the 

latter three monomers via formation of a multitude of strong N-H···O POM 

hydrogen contacts. 

Evidently, the presence of ethyl of methyl groups plays no role in the way the 

monomeric [{Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 )] building block arranges 

itself in this 3-dimensional arquitecture. All efforts to retain both ethyl groups 

where unseuccesful, but judging by the relative positions where the lost ethyl 

group should be, we do not believe that the arrangement would chance 

dramatically. 

105


Figure 4.11 Guanidinium templated tetrahedral arrangement of monomers in 

the unit cell. Color code is the same as in Figure 4.10. Central (A-α-AsW 9 O 34 ) 

unit illustrated in teal for clarity. 

Regarding the connectivity to other cells, a given monomeric building-block is 

as well connected to other three from adjacent cells via coordination of 

terminal O atoms from the tungsten belt to form W2=O2T-Sn ii bridges (Figure 

4.12). This pattern results in a 3-dimensional hybrid organic-inorganic POM 

assembly where each {Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 ) monomeric unit 

is linked to the six nearest neighbours. Similar to 1 – 3, this building unit 

displays chirality, and we noticed in 4 a clockwise orientation like in 1 and 2. 

106


Figure 4.12 Connectivity of a {Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 ) monomeric 

building block (center) with monomers from adjacent unit cells. 

107


Table 4.4. Crystallographic Data of Compound G-4. 

G-4 

Formula C 9 H 52 AsN 9 O 45 Sn 3 W 9 

Mol. Wt. 

(g/mol) 

3092.15 

Crystal colour 

Crystal size 

(mm) 

Crystal system 

Space group 

(Nr.) 

colourless 

0.82 x 0.65 x 0.61 

cubic 

198 

a (Ǻ) 18.0676(14) 

Volume (Ǻ 3 ) 5898.0(8) 

Z 4 

D calcd (g/cm 3 ) 3.404 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

19.376 

129193 

4021 

2631 

0.0886 

0.2383 

GoF 1.017 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

108


4.2.5 Solution Studies (Nuclear Magnetic Resonance) 

Efforts to re-solubilize compound G-4 in water or organic solvents were 

unsuccessful due to the strong N-H···O POM hydrogen contacts, therefore we 

decided to perform multinuclear magnetic resonance studies directly from the 

fresh reaction solution. 

Figures 4.13 and 4.14 illustrate the 1 H and 13 C NMR spectra recorded for title 

polyanion 4. The proton spectra depicts the triplet and quartet expected for an 

ethyl group (1.45 and 1.7 ppm, respectively plus a single peak that we could not 

identify), shifted to the ones encountered for free (C 2 H 5 ) 2 SnCl 2 recorded at the 

same pH value in aqueous solution. Two signals are present in the 13 C spectrum 

of polyanion 4, namely at 10.0 and 23.5 ppm in a 1:1 relative intensity ratio also 

corresponding to the ethyl group. 

Figure 4.13 1 H NMR spectrum of 4 from the fresh reaction mixture in H 2 O/D 2 O 

medium at room temperature. 

109


Figure 4.14 13 C NMR spectrum of 4 from the fresh reaction mixture in H 2 O/D 2 O 

medium at room temperature. 

119 Sn chemical shifts in organotin compounds cover a range of about 4500 ppm, 

whereas δ moves upfield as the coordination number of tin increases 4 → 5 → 6 

→ 7. 6 This phenomena suggest attachment of the organotin group to the 

polyoxometalate framework where according to the solid state structure the 

coordination number of Sn in 4 is six and only one signal (at -215.4 ppm, Figure 

4.15) is expected based on the high symmetry of the monomeric 

{Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 ) unit (ideal C 3v symmetry). Interestingly, 

the 119Sn signal recorded from the fresh reaction mixture is somewhat broad, 

very similar of what Hussein et al. found for his 2-dimensional dimethyltin 

functionalized lone-pair containing trivacant polyoxoarsenate and –antimonate 

compounds. 4a 110


Figure 4.15 119 Sn NMR spectrum of 4 from the fresh reaction mixture in 

H 2 O/D 2 O medium at room temperature. 

The 183 W NMR spectrum of 4 is illustrated in Figure 4.16. Two peaks of relative 

intensity 1:2 are present at -135.0 and -139.5 ppm as expected for the 

{Sn(C 2 H 5 )} 3 (H 2 O) 3 (OH) 3 (A-α-AsW 9 O 34 ) unit where all the belt tungsten atoms are 

equivalent as well as the cap ones. Impurities due to unreacted precursor are 

evident by the presence of signals of lower intensitiy upfield of the major ones. 

111


Figure 4.16 183 W NMR spectrum of 4 from the fresh reaction mixture in 

H 2 O/D 2 O medium at room temperature. 

112


4.3 Conclusions 

In this chapter it was presented the first 3-dimensional mono- and diorganotin 

functionalized polyanions in the solid state, specifically based on the trilacunary 

Keggin polyoxotungstate, as well as the first dimethyltin-containing 

tungstosilicate. The templating effect of the [C(NH 2 ) 3 ] + cation results in a similar 

chiral architecture regardless of the size and charge of the heteroatom. 

Interestingly, the monoethyltin species builds the same arrangement as its 

dimethyltin analogues even when during the reaction one ethyl group is lost. 

Such compounds have the potential to build even more complex molecular 

aggregates by changing the counter-cation, i.e. with other organoammonium 

cations. 

113



(1) Bridgeman, A. J. Chem. Phys. 2003, 287, 55. 


Compounds, Wiley Interscience: New York, 1997. 

(3) Brown, I. D.; Altermatt, D. Acta Cryst. 1985, B41, 244. 

(4) (a) Hussain, F. ; Reicke, M. ; Kortz, U. Eur. J. Inorg. Chem. 2004, 2733. (b) 

Hussain, F. ; Kortz, U. Chem. Commun. 2005, 1191. (c) Kortz, U. ; Hussain, 

F. ; Reicke, M. Angew. Chem. Int. Ed. 2005, 44, 3773. (d) Hussain, F. ; Kortz, 

U. ; Keita, B. ; Nadjo, L. ; Pope, M. T. Inorg. Chem. 2006, 45, 761. (e) Reinoso, 

S.; Dickman, M. H.; Reicke, M.; Kortz, U. Inorg. Chem. 2006, 45, 9014. (f) 

Reinoso, S.; Dickman, M. H.; Kortz, U. Inorg. Chem. 2006, 45, 10422. (g) 

Hussain, F.; Dickman, M. H.; Kortz, U.; Keita, B.; Nadjo, L.; Khitrov, G. A.; 

Marshall, A. G. J. Cluster Sci. 2007, 18, 173. (h) Reinoso, S.; Dickman, M. H.; 

Matei, M. F.; Kortz, U. Inorg. Chem. 2007, 46, 4383. (i) Reinoso, S.; Dickman, 

M. H.; Kortz, U. Eur. J. Inorg. Chem. 2009, DOI: 10.1002/ejic.200801096. 

(5) Pretsch, E.; Bühlmann, P.; Affolter, C.; Badertscher, M. Spektroskopische 

Daten zur Strukturaufklärung organischer Verbindungen; Springer Verlag: 


(6) Davies, A. G. Organotin Chemistry Wiley-VCH: Weinheim, Germany, 2nd. 


114

Chapter V. 2-D Assemblies of Diethyltin Functionalized Heteropolytungstates 

Chapter V. 2-D Assemblies of Diethyltin Functionalized 

Heteropolytungstates 

5.1 2-D Assemblies of Diethyltin Functionalized [A-α-XW9O34] n- 

(X = P V , As V ) Keggin Polytungstates 

The 2-dimensional 

([C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-AsW 9 O 34 )]· 9H 2 O) ∞ (G-5), and 

([C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-PW 9 O 34 )]· 2H 2 O) ∞ 

(G-6) 

polyanions are isostructural and represent the first examples of diethyltin 

functionalized polyaoxoarsenates and –phosphates that constructs a non-planar 

2-D surface in the solid state linked via Sn-O-W bridges from only two of the 

three {Sn(C 2 H 5 ) 2 } 3 groups crafted to the trilacunary [A-α-XW 9 O 34 ] n- unit, different 

to the structures reported in Chapter IV, where all three organotin groups 

participated in the connectivity with other [A-α-XW 9 O 34 ] n- building blocks, hence 

building a 3-dimensional assembly. Polyanions 5 and 6 are isostructural to those 

reported by Hussain et al. 1 with dimethyltin as linkers between the trilacunary 

Keggin units. Interestingly, he reported the use of the As III and Sb III lone-pair 

containing trivacant Keggin polyanions; it is then evident that the different size 

and charge of the heteroatom, as well as the nature of the isomer (β, in the case of 

the dimethyltin containing polyanions) plays no role on the configuration in the 

solid state. Worth to mention that the nature of the counter-cation was different 

also, whereas the compounds reported by Hussain are mixed Cs-Na salts, the 

ones reported here contain only guanidinium cations. 

115



To a solution of (C 2 H 5 ) 2 SnCl 2 (~0.6 mmol) in water (25 mL) solid Na y [A-α- 

XW 9 O 34 ]·nH 2 O (~0.2 mmol), (X = P V , As V ) was added and the pH of the resulting 

solution was adjusted between 4 and 5 with aqueous 1M HCl. After heating at 

40°C for 60 minutes, the solution was cooled to room temperature and aqueous 

1M [C(NH 2 ) 3 ]Cl (0.5 mL) was added. Colorless, block-like single-crystals suitable 

for X-ray diffraction were obtained after approximately 7 days by slow 

evaporation at room temperature. Exact amounts used for each compound are 

described below: 

[C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-AsW 9 O 34 )]· 9H 2 O (G-5). 0.163 g of 

(C 2 H 5 ) 2 SnCl 2 (0.659 mmol) and 0.500 g of Na 9 [A-α-AsW 9 O 34 ]·11H 2 O (0.187 mmol) 

were used and the pH was adjusted to 5. Yield: 0.35 g, 58% based on W. IR 

ν max /cm -1 : 1453(w), 1419(w), 1379(w), 1229(w), 1192(m), 944(s), 860(w), 814(w), 

783(w), 739(w), 678(m), 519(w), 485(w). 

[C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-PW 9 O 34 )]· 2H 2 O (G-6). 0.169 g of 

(C 2 H 5 ) 2 SnCl 2 (0.683 mmol) and 0.500 g of Na 9 [A-α-PW 9 O 34 ]·7H 2 O (0.195 mmol) 

were used and the pH was adjusted to 4. Compound G-6 can also be obtained 

using K 7 [A-α-PW 11 O 39 ]·14H 2 O with the same precursor/(C 2 H 5 ) 2 SnCl 2 molar ratio 

and also at the same pH value of 4. Yield: 0.26 g, 44% based on W. IR ν max /cm -1 : 

1455(w), 1414(w), 1381(w), 1229(w), 1232(w), 1191(m), 1078(m), 1014(m), 941(m), 

908(w), 808(w), 747(w), 669(w), 478(w). 

116



The bands below 1000 cm -1 present in the spectra recorded for compounds G-5 

(Figure 5.1) and G-6 (Figure 5.2) show evidence of presence of the 

polyoxometalate framework, with slight shifting in comparison to the spectra of 

the pure Na 9 [A-α-XW 9 O 34 ]· nH 2 O (X = As V , P V ) trivacant polyoxotungstates. 

Additionally, the strong signal at 1077 cm-1 present in the spectrum of G-6, 

shows clear evidence of the stretching asymmetric (v a ) P-O band present in all 

polyoxotungstophosphates. 2 The presence of the diethyltin group attached to the 

(A-α-XW 9 O 34 ) unit is unambiguously established by the occurrence of two peaks 

of low and medium intensity between 1232 and 1191 cm -1 for G-5 and G-6, 

respectively; characteristic of the bending symmetric vibration (δ sy ) of organotin 

derivatives. 3 Additionally, three signals of weak intensity between 1454 and 1379 

cm -1 are typical to the δ sy and bending asymmetric (δ as ) mode of CH 3 and CH 2 

groups. 4 


117




Figure 5.3 illustrates the thermogramm recorded on a sample of G-5 where its 

thermal decomposition starts with a dehydration step that results in the loss of 

13 water molecules (four from the diprotonated oxygen atoms attached to the 

(C 2 H 5 ) 2 Sn 2+ moiety, see 5.1.4 Single Crystal X-ray Diffraction (XRD) for structural 

details on the compound; and 9 solvation water molecules) after 150 °C [calc 

(found): 7.26% (7.45%)], the heteropolysalt G-5 remains stable without hydration 

molecules up to 194 °C, where immediately afterwards loss of the organic groups, 

i.e. [C(NH 2 ) 3 ] + cations together with the ethyl groups takes place in a series of 

highly overlapping steps below 433 °C. 

118


Compound G-6 experiences a dehydration step that starts at room temperature 

and ends below 153 °C resulting in the loss of 6 water molecules, namely 2 from 

solvation and four belonging to the (C 2 H 5 ) 2 Sn 2+ group [calc (found): G-6, 3.54% 

(3.60%)] . Different as in the case of G-5, compound G-6 does not remain stable 

without hydration molecules and decomposition takes place immediately 

afterwards with a series of highly overlapping exothermic steps resulting in the 

loss of the [C(NH 2 ) 3 ] + counter-cations as well as the C 2 H 5 groups below 400 °C 

(Figure 5.4). 


119




Polyanion 5 and 6 are isostructural and crystallize in the Pnma orthorhombic 

space group (see table 5.1 for crystallographic details). The structure of 5 and 6 is 

best described as a polymeric network composed of [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α- 

XW 9 O 34 )] 3- (Figure 5.4) building blocks (X =As V , P V ) that are linked by Sn-O(W’) 

bridges. This arrangement leads to a 2-D surface which is not planar, but could 

be described as a ladder with a zig-zag backbone where the individual levels are 

ornamented by ethyl groups. 

The monomeric building block in 5 and 6 is illustrated in Figure 5.5 with atom 

labeling. Assuming free rotation of the ethyl groups, such monomeric block has 

an ideal C 3v symmetry. 

120


The three organotin groups attached to each monomeric unit of 5 and 6 contain 

tin centers that are octahedrally coordinated by four oxo and two ethyl groups 

which are positioned trans to each other. However, only two organotin groups 

are structurally equivalent (Sn1) and different from the third (Sn2). Both 

equivalent Sn1 tin atoms participate in bonding to other [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α- 

XW 9 O 34 )] 3- units via Sn1-O2WS-W’ bridges (Figure 5.6), whereas the oxygen 

atoms attached to Sn2, i.e. O3W are diprotonated based on bond-valence sum 

calculations. 5 Furthermore, the distances between Sn2 and O3W are rather long, 

i.e. 2.60(3) and 2.67(3) Å (see Table 5.1) for polyanion 5 and 6, respectively, fact 

that makes less likely that such oxygen atoms participate in further bonding. 


[{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α- XW 9 O 34 )] 3- monomeric building-block in 5 and 6. Color 

code: WO 6 octahedra: teal; X: yellow [X = As V (5), P V (6)]; C: black; O: red; Sn: 

olive green; H: white. 

121


Comparison of the C-Sn-C angles in the both non-equivalent tin atoms shows 

exactly the opposite tendency of what Hussein et al. observed for his dimethyltin 

functionalized lone-pair containing trivacant polyoxoarsenate and – antimonate 1 , 

namely that the angle in the two equivalent tin atoms, i.e. those that participate 

in further bonding are larger 165.9(9) and 164.6(9) for 5 and 6 respectively, than 

that of the unique (Sn2) tin atom, namely 141.6(16) and 137.9(15); also for 5 and 6, 

respectively. Evidently, the similarity of both angles for the two kinds of tin 

atoms reflects the comparable size of the As V and P V heteroatoms, hence their 

influence in the bond angle values is not as evident as in the case of As III vs. Sb III . 

Table 5.1 Selected Bond Lengths (Å) and Angles (°) of Polyanions 5 and 6. * 

5 6 

Sn1-O3WS 2.155(13) 2.161(11) 

Sn1-O4WS 2.109(13) 2.102(11) 

Sn1-O1S1 2.328(19) 2.385(19) 

Sn1-O2WS 2.449(13) 2.442(11) 

Sn1-C1S1 2.15(2) 2.14(2) 

Sn1-C3S1 2.12(3) 2.10(2) 

C1S1-Sn1-C3S1 165.9(9) 164.6(9) 

Sn2-O1WS 2.098(15) 2.065(12) 

Sn2-O3W 2.60(3) 2.67(3) 

Sn2-C1S2 2.21(6) 2.12(3) 

Sn2-C3S2 2.07(4) 2.05(4) 

C3S2-Sn2-C1S2 141.6(16) 137.9(15) 

* Refer to Table 5.2 for a more complete crystallographic data description of G-5 and G-6. 

122


Each monomeric [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-XW 9 O 34 )] [ (X = As V (5); P V (6) ] 

building block unit is connected to other two units through the two equivalent 

tin atoms by means of O-Sn-O(=W) bridges, i.e. to one terminal oxygen atom 

from the cap triad of a neighbor monomeric unit as illustrated in Figure 5.6 (left). 

Figure 5.6 Combined polyhedral/ball-and-stick representation of the 2-D solidstate 

structure of [C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-XW 9 O 34 )]· nH 2 O [X = As V (5), 

P V (6)]. Left: front view; right: side view. Color code: WO 6 octahedra: sea green; 

XO 4 tetrahedra: yellow, all other atoms correspond to the same colour codes as 

depicted in Figure 5.5. Hydrogen atoms omitted for clarity. 

123


Figure 5.6 (right) depicts a side view of polyanions 5 and 6. The equivalent tin 

atoms that connect further monomeric units one level above force a change of 

direction of the [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 4 (A-α-XW 9 O 34 )] unit resulting in a zig-zag 

configuration where the Sn(OH 2 ) 2 O 2 groups interchange positions from right to 

left. 

Table 5.2. Crystallographic Data of Compounds G-5 and G-6. 

G-5 G-6 

Formula C 15 H 74 AsN 9 O 47 Sn 3 W 9 C 15 H 60 N 9 O 40 PSn 3 W 9 

Mol. Wt. 

(g/mol) 

3218.39 3048.34 

Crystal colour colourless colourless 

Crystal size 

(mm) 

0.31 x 0.29 x 0.06 0.44 x 0.40 x 0.25 

Crystal system orthorombic orthorombic 

Space group 

(Nr.) 

62 62 

a (Ǻ) 23.5280(10) 23.5804(8) 

b (Ǻ) 15.5435(6) 15.4824(5) 

c (Ǻ) 18.6191(9) 18.5964(7) 

Volume (Ǻ 3 ) 6809.1(5) 6789.2(4) 

Z 4 4 

D calcd (g/cm 3 ) 3.024 3.030 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

16.784 16.378 

82554 324420 

8141 9386 

6027 7433 

0.0563 0.0643 

0.2058 0.2009 

GoF 1.004 1.070 

a R(F) = Σ||F o | - |F c ||/Σ|F o |; wR(F 2 ) = {Σ[w(F 2 o - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

124


Compounds G-5 and G-6 resulted in good quality single-crystals with the 

addition of a 1M solution of guanidinium chloride, whereas the [C(NH 2 ) 3 ] + 

cation stabilizes this POM arrangement by holding it together via formation of a 

multitude of strong N-H···O POM hydrogen bridges. 

5.1.5 Conclusions 

Polyanions 5 and 6 represent the first examples of a 2-dimensional architecture 

stabilized by diethyltin electrophiles, with exactly the same arrangement in the 

solid state as those reported by Hussain et al. 1 but with phosphorous (V) and 

arsenic (V) as heteroatoms in the trivacant Keggin [A-α-XW 9 O 34 ] building block, 

whereas those with dimethyltin moieties as linkers were synthesized with the 

lone-pair containing arsenic (III) and antimony (III) trilacunary Keggin. 

Interestingly, the pH at which the reactions were conducted had the values of 5.0 

and 4.0 for polyanions 5 and 6, respectively, whereas the As(III) and Sb(III) 

analogues were synthesized both at pH 3.0. Also the reaction conditions were 

similar in all cases but it seems that the pH value played the major role, since, for 

example using the same counter-cation, namely guanidinium in the reaction 

between the arsenic (V) trilacunary Keggin precursor and diethyltindichloride at 

pH 3.0, the product obtained was a 3-dimensional assembly (see Chapter IV: 4.2 

3-D Assembly of an Ethyltin Functionalized [A-α-AsW 9 O 34 ] 9- Keggin polyoxotungstate). 

125



(1) Hussain, F. ; Reicke, M. ; Kortz, U. Eur. J. Inorg. Chem. 2004, 2733. 

(2) a) Contant, R. Can J. Chem. 1987, 65, 568. b) Tourné, C.; Revel, A.; Tourné, 

G. Rev. Chim. Mine. 1977, 14, 757. c) Highfield, J. G.; Moffat, J. B. J. Catal. 

1984, 88, 177. d) Highfield, J. G.; Hodnett, B. K.; Monagle, J. B.; Moffat, J. B. 

Proc. 8 th . Int. Congr. Catal. Dechema, Frankfurt am Main, 1984, 167. e) 

Highfield, J. G.; Moffat, J. B. Stud. Surf. Sci. Catal. 1984, 19, 77. 







126

Chapter VI. 1-D Assemblies of Diorganotin Functionalized Hetero- and Isopolytungstates 

Chapter VI. 1-D Assemblies of Diorganotin Functionalized 

Hetero- and Isopolytungstates 

6.1 The [{Sn(C2H5)2}6(H2O)6(B-β-XW9O33)2] 6- (X = Sb III , As III ) Lone- 

Pair Polyoxotungstate Dimer and its 1-D Architecture in the Solid 

State. 

Reaction of 3 equivalents of (C 2 H 5 ) 2 SnCl 2 with the trilacunary [A-β-SbW 9 O 33 ] 9- 

antimony containing trilacunary Keggin in acidic, aqueous conditions resulted in 

the novel diethyltin functionalized nonatungstoantimmonate dimmer that forms 

a 1-D chain of dimers in the solid state, namely: 

([C(NH 2 ) 3 ] 6 [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-SbW 9 O 33 ) 2 ]· 7H 2 O) ∞ 

(G-7) 

Our efforts to obtain the analogue compound with As III using [A-β-AsW 9 O 33 ] 9- as 

precursor at similar conditions were unsuccessful, therefore we decided to use 

K 14 [[As III 2 W 19 O 67 (H 2 O)] as precursor, which in any case is conformed of two [A-β- 

AsW 9 O 33 ] units. Adjusting the pH to a slightly more basic value in comparison to 

that used for obtaining G-7, the isostructural compound in the solid state: 

([C(NH 2 ) 3 ] 6 [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-AsW 9 O 33 ) 2 ]· 8H 2 O) ∞ 

(G-8) 

was obtained. Interesting to note that isomerisation from (B-α-XW 9 O 33 ) to (B-β- 

XW 9 O 33 ) takes place for Sb III as well as for As III . Such change is facilitated in 

aqueous, acidic medium. 1,2 Hussein et al. 3 observed the same phenomena for the 

2-dimensional hybrid organic-inorganic materials functionalized with 

dimethyltin groups reported in 2004. 3 G-7 and G-8 crystallize as guanidinium 

salts. 

127



[C(NH 2 ) 3 ] 6 [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-SbW 9 O 33 ) 2 ]· 7H 2 O (G-7): 

To a solution of 0.152 g (C 2 H 5 ) 2 SnCl 2 (0.611 mmol) in water (25 mL) solid Na 9 [Bα-SbW 

9 O 33 ]· 27H 2 O (0.500 g, 0.175 mmol) was added and the pH of the resulting 

solution was adjusted to 3.0 with aqueous 1M HCl. After heating at 40°C for 60 

minutes, the solution was cooled to room temperature and filtered to separate 

any unreacted material. Aqueous [C(NH 2 ) 3 ]Cl (0.5 mL) 1M was added. Colorless, 

block-like single-crystals suitable for X-ray diffraction were obtained after 

approximately 10 days by slow evaporation at room temperature. Yield: 0.38 g, 

37% (based on W). IR ν max /cm -1 : 1456(w), 1419(w), 1379(w), 1231(w), 1195(m), 

947(s), 865(w), 785(s), 668(m), 472(w), 420(w). 

[C(NH 2 ) 3 ] 6 [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-AsW 9 O 33 ) 2 ]· 8H 2 O (G-8): 

0.500 g (0.095 mmol) of K 14 [[As III 2 W 19 O 67 (H 2 O)] were added to an aqueous 

solution (25 mL) of 0.096 g (0.388 mmol) of (C 2 H 5 ) 2 SnCl 2 . After complete 

dissolution, the pH of the mixture was adjusted to 5.0 with HCl 0.5 M. The 

solution was heated at 80 °C for 1 hour upon stirring. When the reaction mixture 

was cooled down to room temperature it was filtrated to separate all remains of 

unreacted material. 0.3 mL of [C(NH 2 ) 3 ]Cl 1M was added to the mixture. After 

approx. 14 days, colourless plate-like crystals suitable for X-ray were obtained by 

slow evaporation at room temperature. Yield: 0.25 g, 43% (based on W). IR 

ν max /cm -1 : 1454(w), 1417(w), 1375(w), 1232(w), 1194(m), 1023 (sh), 950(s), 871(w), 

794 (s), 727(sh), 671(m), 540(sh), 506(sh), 476(m). 

128



Figure 6.1 and 6.2 illustrates the FT-infrared spectrum recorded on a sample of 

G-7 and G-8, respectively. The presence of the polyoxotungstate framework is 

evident from the characteristic signals below 1000 cm -1 , which are slightly shifted 

from those from the pure precursors Na 9 [B-α-SbW 9 O 33 ]· 27H 2 O 4 and Na 9 [B-α- 

AsW 9 O 33 ]· 27H 2 O 5 . The existence of the (C 2 H 5 ) 2 Sn 2+ moiety in G-7 and G-8 can 

be established unequivocally by two peaks of low and medium intensity at 1232 

and 1194 cm -1 present in both compounds, which are characteristic of the 

bending symmetric vibration of organotin derivatives. 6 Another three peaks of 

medium intensity between 1455 and 1379 cm -1 corresponds to the bending 

symmetric and asymmetric vibration modes of the CH 3 and CH 2 organic 

groups. 7 


129




Thermal stability was investigated on a sample of compounds G-7 and G-8, 

whereas for the former thermal decomposition starts with a dehydration step 

resulting in the loss of 13 water molecules below 150 °C [calc (found): 3.73% 

(3.40%)]. The compound remains stable without hydration molecules until 182 °C 

and immediately afterwards release of the organic [C(NH 2 ) 3 ] + cations and the 

C 2 H 5 groups takes place between 182 and 411 °C in a single, continuous step. The 

polyoxotungstates framework decomposes subsequently (Figure 6.3). 

130



Figure 6.4 portray the thermal analysis recorded on a sample of compound G-8. 

Similar to its analogue compound G-7, the former experiences a dehydration 

step that starts at room temperature and ends below 142 °C with the loose of 14 

water molecules [calc (found): 4.08% (4.05%)]. But instead of remaining stable 

without hydration molecules up to a given higher temperature as the latter 

compound, G-8 starts immediately to loose its organic guanidinium and ethyl 

groups in two exotermic steps below 445 °C, followed by decomposition of the 

metal-oxo framework above 800 °C. 

131




Polyanions 7 and 8 crystallize in the P -1 triclinic space group and are composed 

of two [B-β-XW 9 O 33 ] (X = Sb III , As III ) units linked together via two long O(W)-Sn- 

O(W´) bridges. Each unit has an ideal C 1 symmetry providing that the ethyl 

groups can rotate freely, whereas for the dimeric unit corresponds to a C i 

symmetry. Each [B-β-XW 9 O 33 ] half has three (C 2 H 5 ) 2 Sn 2+ moieties attached to the 

free sites of the Keggin polyanion, whereas two of them are six coordinated in an 

octahedral fashion and the third one pentacoordinated in a trigonal bypiramidal 

manner (Figure 6.5). 

132



[{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-XW 9 O 33 ) 2 ] (X = Sb III , As III ) Dimmer. Color code: WO 6 

octahedra (teal); tin (olive green), carbon (black), oxygen (red), X (yellow) and 

hydrogen (white). 

Precisely the latter (C 2 H 5 ) 2 SnO 3 group does not participate in further bonding, 

while the (C 2 H 5 ) 2 SnO 4 moiety located further away from the one that links the 

second [B-β-XW 9 O 33 ] half (Sn3), connects to further [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β- 

AsW 9 O 33 ) 2 ] dimmers constructing a one-dimensional chain of dimmers as 

depicted in Figure 6.6. Reaction in acidic media from the lone-pair containing 

precursors [B-α-XW 9 O 33 ] (X = Sb III , As III ) results in change from the α to the β 

isomer as already mentioned, this phenomena was already observed in similar 

conditions in our group. 3 Since the ethyl groups are rather bulky, and the β 

isomer guarantees more space in the lacuna 8 , steric effects can be disregarded. 

On the other hand, since both polyanions 7 and 8 crystallize as guanidinium salts, 

the strong N-H···O POM interactions maintain the whole structure stable. 

133


Figure 6.6 Combined Polyhedral/ball-and-stick representation of the 1-D chain 

composed of [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-XW 9 O 33 ) 2 ] (X = Sb III , As III ) Dimmers. Same 

color code as for Figure 6.5. Hydrogen atoms omitted for clarity. 

Oxygen atoms corresponding to the pentacoordinated (C 2 H 5 ) 2 SnO 3 diethyltin 

group and those that does not participate in further bonding from the 

(C 2 H 5 ) 2 SnO 4 groups are diprotonated based on the Bond Valence Sum (BVS) 9 

calculations performed on polyanions 7 and 8. 

Table 6.1 illustrates all the bond distances of the atoms connected to each pentaand 

hexacoordinated tin atom. Interesting to note that in the (C 2 H 5 ) 2 SnO 3 group 

for both polyanions 7 and 8, the C-Sn-C angle is distinctly shorter [121.8(5) and 

128.1(12)° for 7 and 8, respectively] than those of the other two (C 2 H 5 ) 2 SnO 4 

octahedrally arranged groups, what corresponds to the trigonal bypiramidal 

geometry, whereas for the latter cases the angles need to be larger due to steric 

effects. 

134


Table 6.1 Selected Bond Lengths (Å) and Angles (°) of Polyanions 7 and 8. 

7 8 

Sn1-O1S1 2.002(6) 1.975(11) 

Sn1-O5S1 2.046(7) 2.078(11) 

Sn1-O1SN 2.799(16) 2.815(8) 

Sn1-C1S1 2.110(14) 2.150(4) 

Sn1-C3S1 2.124(11) 2.160(2) 

C1S1-Sn1-C3S1 121.8(5) 128.1(12) 

Sn2-O5S2 2.038(7) 2.034(12) 

Sn2-O7S2 2.122(6) 2.089(11) 

Sn2-O2Sn 2.675(3) 2.716(10) 

Sn2-O5T 2.441(7) 2.455(12) 

Sn2-C1S2 2.098(12) 2.130(2) 

Sn2-C3S2 2.123(11) 2.120(2) 

C1S2-Sn2-C3S2 147.4(5) 145.1(8) 

Sn3-O9S3 2.081(6) 2.092(11) 

Sn3-O2S3 2.119(6) 2.131(12) 

Sn3-O6T 2.653(3) 2.676(10) 

Sn3-O3Sn 2.334(9) 2.320(14) 

Sn3-C1S3 2.127(10) 2.117(17) 

Sn3-C3S3 2.104(11) 2.170(2) 

C1S3-Sn3-C3S3 144.5(4) 151.6(8) 

135


The Sn2-O5T bond that connects both [B-β-XW 9 O 33 ] halves are between 2.441(7) 

and 2.455(12) Å for 7 and 8, respectively but even longer are the Sn3-O6T bonds 

that links each [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-XW 9 O 33 ) 2 ] dimmer to the left and right 

(Figure 6.6), which are approx. 0.2 Å longer than Sn2-O5T [2.653(3) for polyanion 

7 and 2.676(10) Å for polyanion 8]. 

Reinoso et al. reported in 2006 10 a dimethyltin functionalized hexatungstate, 

which forms a 1-dimensional chain in the solid state, where the tin atom is 

pentacoordinated in slightly distorted trigonal bypiramidal geometry. The C-Sn- 

C angle in that case was found to be 124.8(4) °, very similar to those described for 

polyanions 7 and 8. 

Crystallographic data of 7 and 8 is presented in Table 6.2. 

136


Table 6.2. Crystallographic Data of Compounds G-7 and G-8. 

G-7 G-8 

Formula C 15 H 61 N 18 O 40 SbSn 3 W 9 C 15 H 62 N 9 O 40 AsSn 3 W 9 

Mol. Wt. 

(g/mol) 

3266.19 3094.30 

Crystal colour colourless colourless 

Crystal size 

(mm) 

0.25 x 0.18 x 0.05 0.14 x 0.05 x 0.02 

Crystal system triclinic triclinic 

Space group 

(Nr.) 

2 2 

a (Ǻ) 11.4638(13) 11.5170(6) 

b (Ǻ) 13.1658(17) 13.1080(7) 

c (Ǻ) 21.394(2) 21.3259(11) 

α 77.956(6) 79.938(2) 

β 88.443(5) 89.817(2) 

γ 65.382(6) 65.561(2) 

Volume (Ǻ 3 ) 2864.3(6) 2877.3(3) 

Z 1 1 

D calcd (g/cm 3 ) 3.714 3.560 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

19.851 19.855 

117090 145205 

13168 14171 

11446 11063 

0.0340 0.0836 

0.0861 0.1556 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

137


6.2 A Lone-Pair Polyoxotungstatoarsenate [{Sn(C2H5)2}3(H2O)2(B-β- 

AsW9O33)] 3- and its 1-Dimensional Arrangement through Diethyltin 

Bridges. 

Interaction of the trilacunary lone-pair containing nonatungstoarsenate Keggin 

polyanion towards diethyltin dichloride in aqueous, acidic media at mild 

temperature conditions resulted in the novel diethyltin functionalized 

polyoxometalate that forms a one-dimensional chain in the solid state via two O- 

Sn-O(W) bridges, namely: 

([C(NH 2 ) 3 ] 3 [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )]· H 2 O) ∞ 

(G-9) 

Polyanion 9 crystallizes as a guanidinium salt and this compound represents the 

first example of a one-dimensional architecture in a zig-zag fashion by means of 

oxo-tin-oxo bridges from two (C 2 H 5 ) 2 SnO 3 groups grafted at the vacant sites of 

the Keggin polyanion and the two lower terminal oxygen atoms from two 

adjacent {W 3 O 13 } triads. 


0.147 g of (C 2 H 5 ) 2 SnCl 2 (0.593 mmol) were dissolved in 25 mL of water and 

stirred until complete dissolution. 0.500 g of Na 9 [B-α-AsW 9 O 33 ]· 27H 2 O (0.169 

mmol) were added to the mentioned solution and the pH was adjusted to 3.0 

with HCl 2 M. After the mixture was left for 60 minutes with continuous stirring 

at 40 °C, filtration followed in order to separate unreacted material. Few drops 

(0.3 mL) of a 1 M solution of [C(NH 2 ) 3 ]Cl were added to the filtrate and after 10 

to 12 days of slow evaporation at room temperature; good quality, colourless 

crystals adequate for X-ray analysis were obtained. 

138


Yield: 0.28 g, 54% (based on W). IR ν max /cm -1 : 1453(w), 1416(w), 1379(w), 1234(w), 

1191(m), 1067 (sh), 1021 (sh), 946(s), 882(w), 813 (s), 735 (w), 678 (m), 611 (sh), 532 

(w), 477 (m), 422 (w). 


In Figure 6.7 is illustrated the FT-IR spectrum recorded on a sample of G-9. The 

weak signal at 1234 cm -1 and the one of medium intensity at 1191 cm -1 provide 

evidence of the presence of the (C 2 H 5 ) 2 Sn 2+ group attached to the 

polyoxotungstate framework. Such bands are characteristic of the bending 

symmetric vibration (δ sy ) of organotin derivatives. 6 Three bands of medium 

intensity at 1453, 1416 and 1379 cm -1 corresponds to δ sy and δ as of the CH 3 group, 

and δ sy CH 2 , respectively, whereas the series of bands present below 1000 cm -1 

are characteristic of the metal-oxo bending and stretching modes of the 

polyoxotungstoarsenate framework, which in the case of G-9 are shifted of those 

present in the pure trivacant Na 9 [B-α-AsW 9 O 33 ]· 27H 2 O Keggin polyanion. 5 


139



Thermal decomposition of G-9 starts with a dehydration step from room 

temperature up to 123 °C where three H 2 O molecules are released [calc (found): 

1.79% (1.94%)]. The specie remains stable without water molecules up to 157 °C 

and from this point two exothermic steps are visible, the first one between 157 

and 358 °C, and the second between 358 – 418 °C. Precisely in this gap of 261 °C, 

the organic groups (guanidinium cations as well as the ethyl groups) are lost 

with the subsequent tear down of the polyoxotungstate framework below 600 °C 

(Figure 6.8). 


140



Polyanion 9 crystallizes as a guanidinium salt in the Pnma orthorhombic space 

group (62). It is composed of a (B-β-AsW 9 O 33 ) building unit, which has an ideal 

C s symmetry. Its vacant sites are occupied with two equivalent pentacoordinated 

tin atoms [(C 2 H 5 ) 2 SnO 3 ] and one unique hexacoordinated tin atom [(C 2 H 5 ) 2 SnO 4 ]. 

The former presents a distorted trigonal bypiramidal geometry with the ethyl 

groups trans to each other in the axial positions, whereas the latter shows an 

octahedral arrangement also with its ethyl groups trans to each other and the 

oxygen atoms in the equatorial positions. Figure 6.9 portrays the 

[{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )] main unit with atom labelling. 


[{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )]monomeric building-block in 9. Color code: 

WO 6 octahedra: light green; As: yellow; C: black; O: red; Sn: olive green; H: light 

grey. 

141


Interestingly, the C-Sn-C angles in both penta- and hexacoordinated tin atoms 

are rather similar [141.1(7) and 142.0(14) °, respectively], different from what we 

observed in polyanions 7 and 8 for the pentacoordinated tin atom. Possibly steric 

reason account for this rather wide angle, since Sn1 links another 

[{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )] unit via O2S1-Sn1-O2T bridges, therefore 

repulsion due to the bulkiness of this second unit would account for a bigger 

separation of the ethyl groups, whereas in the case of 7 and 8, no further linkage 

was present in those pentacoordinated tin atoms. On the other hand, the Sn1- 

O2T bond distance [2.414(11) Å] is rather long compared to those that connect 

Sn1 with the oxygen atoms of the vacant sites of the Keggin polyanion, namely 

1.986(10) for Sn1-O1S1 and 2.120(10) Å in the case of Sn1-O2S1. 

Bond Valence Sum (BVS) calculations 9 performed on polyanion 9 disclosed that 

the oxygen atom attached to Sn2 (O2S2) is diprotonated. Exactly as in the case of 

the reaction conditions used to obtain G-7 and G-8; isomerisation from the α to 

the β species took place as observed in the solid structure of 9, where aqueous, 

acidic media was also used. It seems that the gain in space in the vacant site of 

the Keggin nonatungstoarsenate favours the attachment of the rather bulky 

diethyltin groups. Selected bond distances and angles are showed in Table 6.3. 

142



9 

Sn1-O1S1 1.986(10) 

Sn1-O2S1 2.120(10) 

Sn1-O2T 2.414(11) 

Sn1-C1S1 2.09(2) 

Sn1-C3S1 2.157(16) 

C1S1-Sn1-C3S1 141.1(7) 

Sn2-O1S2 2.090(11) 

Sn2-O2S2 2.24(2) 

Sn2-C1S2 2.09(3) 

Sn2-C3S2 2.11(4) 

C1S2-Sn2-C3S2 142.0(14) 

The linkage fashion in which 9 constructs a 1-dimensional chain is illustrated in 

Figure 6.10. As mentioned before, connection between [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β- 

AsW 9 O 33 )] units takes place through two O-Sn-O(=W) bridges from the 

pentacoordinated tin atoms in a “zig-zag” approach. It is then not surprising, 

that there is simply no more room for an extra oxygen atom that would be 

related to Sn1, hence supporting the hypothesis of a pentacoordinated tin atom 

mainly due to steric reasons. 

143



1-dimensional arrangement of 9 composed of [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β-AsW 9 O 33 )] 

building-blocks. Same colour code as for Figure 6.9. 

In Table 6.4 further crystallographic data of compound G-9 is presented. 

144



G-9 


Mol. Wt. 

(g/mol) 

3022.24 


Crystal size 

(mm) 


Space group 

(Nr.) 

colourless 

0.29 x 0.19 x 0.17 

orthorombic 

62 

a (Ǻ) 19.8709(10) 

b (Ǻ) 18.2659(8) 

c (Ǻ) 13.0944(7) 

Volume (Ǻ 3 ) 4752.7(4) 

Z 4 

D calcd (g/cm 3 ) 4.089 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

24.017 

231004 

5495 

4420 

0.0430 

0.1203 

GoF 1.033 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

145


6.3 The Dimethyltin Functionalized Eicosatungstodiphosphate 

Polyanion: [{Sn(CH3)2(H2O)}2(P2W20O70K(H2O)2)] 5- 

In this section we report on the novel disubstituted eicosatungstodiphosphate 

polyanion with dimethyltin groups: 

([C(NH 2 ) 3 ] 5 [{Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 K(H 2 O) 2 )] · 18H 2 O) ∞ (G-10) 

G-10 represent the first functionalized polyoxotungstate with dimethyltin 

electrophiles based on the monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- (P 2 W 20 ) polyanion. 

Stoichiometric quantities of P 2 W 20 and dimethyltindichloride in aqueous, acidic 

media resulted in 10, which crystallize as guanidinium salt and was 

characterized in the solid state by single crystal diffractometry, FT-Infrared and 

thermogravimetric analysis. Solution studies carried on 10 by means of 

multinuclear NMR as the more soluble lithium salts revealed that the organotin 

moieties did not remained attached to the [P 2 W 20 O 70 K(H 2 O) 2 ] polyanion. 


0.500 g (0.087 mmol) of K 10 [P 2 W 20 O 70 K(H 2 O) 2 ] · 24H 2 O were added to an aqueous 

(20 mL) solution of 0.042 g (0.192 mmol) of (CH 3 ) 2 SnCl 2 upon stirring; after 

complete dissolution the pH was adjusted to 3 with HCl 1M and the mixture was 

stirred for another 60 min. at 40°C, after cooling down to room temperature 0.5 

mL of C(NH 2 ) 3 Cl 1M were added to the reaction mixture following filtration. 

Slow evaporation at room temperature led to a crystalline colourless material 

(Yield: 0.18 gr, 32% based on W) from which a suitable single crystal was choose 

to perform a crystallographic measurement. IR ν max /cm -1 : 1666 (vs), 1562 (sh), 

1399 (w), 1203 (w), 1091 (s), 1065 (s), 1021 (m), 1005 (w), 955 (m), 923 (m), 856 (w), 

789 (w), 740 (w), 627 (w), 594 (w), 575 (vw), 518 (m), 444 (w),413 (w). 

146



The infrared spectra (Figure 6.11) recorded on G-10 confirms the presence of the 

P 2 W 20 unit in agreement to the assignment of Contant 11 ; i.e. asymmetric 

stretching (v as ) P-O frequencies were observed at 1089 and 1072 cm -1 ; as well as 

the W-O t v as bands at 953 and 921 cm -1 . The signals found at 858, 789 and 746 cm - 

1 are assigned to the stretching vibrations of W-O-W bridges. The P-O bend band 

was found at 595 cm -1 . Furthermore, the presence of the diethyltin group 

attached to the P 2 W 20 unit is unambiguously established by the presence of a 

peak of low intensity at 1213 cm -1 , characteristic of the bending symmetric 

vibration (δ sy ) of organotin derivatives. 6 Additionally, two signals of weak 

intensity at 1402 and 1385 cm -1 corresponding to the bending symmetric and 

antisymmetric modes of CH 3 accounting for its presence of the attached to the tin 

atom. 7 


147



The thermogramm recorded on a sample of G-10 shows two very clear steps as 

depicted in Figure 6.12. The first one represents a dehydration process that starts 

at room temperature and ends below 190 °C resulting in the loss of 20 water 

molecules [calc (found): 6.07% (6.22%)]. The second step consists on the loose of 

the organic species (guanidinium cations and the methyl groups) in a smooth 

exothermic stage starting immediately after the hydration molecules were lost 

and ends below 539 °C. Afterwards a very small loose of mass is evident on the 

remaining material (the P2W20 framework), accounting of the high thermal 

stability of this polyanion, opposite of all species reported before on which after 

complete loose of the organic groups, clear destroy of the polyoxotungstates 

building block was evident. 


148



Polyanion 10 was synthesized by reacting one equivalent of [P 2 W 20 O 70 (H 2 O) 2 K] 10- 

(P 2 W 20 ) with two equivalents of (CH 3 ) 2 Sn 2+ in aqueous, acidic media at moderate 

temperature and the product crystallized as a guanidinium salt (G-10) in the 

monoclinic space group P2 1 /m. Polyanion 10 has and ideal C 2v symmetry 

provided that the ethyl groups can freely rotate and it is composed of two [A-α- 

PW 9 O 34 ] (PW 9 ) units bridged by two octahedrally coordinated tungsten atoms in 

the equatorial plane. Each of these two tungsten atoms is connected to two edge 

shared tungsten octahedra from each (PW 9 ) through four oxygen bridges, 

leaving two terminal oxygens: one facing the cavity of the polyanion and one, 

diprotonated, in the opposite direction. The vacant site, corresponding to a third 

octahedrally coordinated tungsten atom in the plenary [P 2 W 21 O 71 (OH 2 ) 3 ] 6- 12a , is 

occupied by two hexacoordinated Sn(IV) atom, i.e. (CH 3 )SnO 4 resulting in a C 2v 

symmetry (Figure 6.13). Crystallographic studies on the potassium salt of the 

P 2 W 20 species performed by independent groups 12 revealed a K + atom in the 

cavity, which is six-coordinated to oxygen of the polyanion and holds both (PW 9 ) 

units together. 

149


Figure 6.13. Combined polyhedral and ball-and-stick representation of a 

{Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 K(H 2 O) 2 ) 5- unit of polyanion 10. Front side (left) and 

upper side (right). Colour code: WO 6 octahedra (dark red); phosphorous 

(yellow); oxygen (red); tin (olive green); potassium (plum); carbon (black); 

hydrogen (white). 

Each tin atom is hexacoordinated with two methyl groups in trans position to 

each other whereas the four equatorial sites are occupied with oxygen atoms, 

two in cis positions are connected to the P 2 W 20 vacant site via Sn-O(=W) bridges 

while a third one connects further P 2 W 20 units in a “zig-zag” fashion constructing 

a 1-dimensional chain (Figure 6.14). The fourth oxygen atom was found to be 

diprotonated according to Bond Valence Sum (BVS) calculations. 9 150


The Sn-O-W distances in polyanion 10 are 2.137 (15) and 2.186 (15) Å 

respectively, whereas the Sn-OH 2 bond is rather long, namely 2.326 (17) Å as well 

as the Sn-O t distance of 2.574(2) Å (where O t is the terminal oxygen of one belt 

WO 6 of the upper PW9 half of the adjacent {Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 (H 2 O) 2 K) 5- 

unit). The C-Sn-C angle is 165.5° (10). 

Figure 6.14. Combined polyhedral and ball-and-stick representation of a 1-D 

chain composed of {Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 (H 2 O) 2 K) 5- units. Colour code is 

the same as in Figure 6.13. 

Further crystallographic information is on hand in Table 6.5. 

151



G-10 

Formula C 9 H 86 KN 15 O 92 P 2 Sn 2 W 20 

Mol. Wt. 

(g/mol) 

5892.09 


Crystal size 

(mm) 


Space group 

(Nr.) 

colourless 

0.20 x 0.15 x 0.09 

monoclinic 

11 

a (Ǻ) 13.844(2) 

b (Ǻ) 19.275(2) 

c (Ǻ) 18.031(2) 

β (°) 100.700(7) 

Volume (Ǻ 3 ) 4727.8(11) 

Z 2 

D calcd (g/cm 3 ) 4.177 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

24.943 

101350 

12062 

7550 

0.0623 

0.1961 

GoF 1.047 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

152


6.4 The Diethyltin Functionalized Hexatungstate Isopolyanion: 

[{Sn(C2H3)2}2(W6O22)] 4- 

Here we report on the isohexatungstate polyanion and its 1-dimensional 

architecture in the solid state by means of diethyltin (C 2 H 5 )Sn 2+ bridges. Reaction 

of 3 equivalents of sodium tungstate dihydrated with one equivalent of 

diethyltindichloride in aqueous, neutral media resulted in: 

([C(NH 2 ) 3 ] 4 [{Sn(C 2 H 5 ) 2 } 2 (W 6 O 22 )]·5H 2 O) ∞ 

(G-11) 

Which crystallizes as a guanidinium salt. Interestingly, both tin atoms are 

pentacoordinated in a distorted trigonal bipyramidal geometry [(C 2 H 5 )SnO 3 ] 

without water molecules attached to them, whereas the ethyl groups are cis to 

each other. Compound G-11 is isostructural to that reported by Reinoso et al. 13 in 

which dimethyl tin moieties connects the hexatungstate units. 


0.500 g (1.516 mmol) of Na 2 WO 4 ·2H 2 O were added to a 25 mL aqueous solution 

of 0.123 g (0.506 mmol) of (C 2 H 5 ) 2 SnCl 2 . The pH value was measured after the 

reactants were completely solubilized and found to be 6.7. The mixture was left 

upon stirring for 30 minutes at 70 °C and after the solution cooled down to room 

temperature, the pH value was measured again and no important difference was 

established (pH = 6.9). To the colourless solution 0.5 mL of [C(NH 2 ) 3 ]Cl 1 M was 

added and left to slow evaporation at room temperature. After approx. 7 days 

colourless, block-like crystals appeared from which one was selected for x-ray 

measurements.Yield: 0.46 g, 43% based on W. IR ν max /cm -1 : 1458(w), 1417(w), 

1384(w), 1236(w), 1187(w), 1121(w), 1063 (w), 1014(w), 941(m), 858(m), 831(m), 

802(w), 752(w), 661(w), 663(w), 540(w), 481(w), 447(w), 430(w). 

153



As depicted in Figure 6.15, evidence of the presence of the ethyltin moiety is 

found based on the two signals of very low intensity at 1236 and 1187 cm -1 , 

characteristic of the bending symmetric vibration (δ sy ) of organotin derivatives. 6 

On the other hand, another three peaks of low intensity at 1458, 1417 and 1384 

cm -1 are representative to the δ sy and bending asymmetric (δ as ) mode of CH 3 and 

CH 2 groups. 7 The series of signals below 1000 cm -1 are attributable to the 

tungsten-oxygen bending and stretching modes. 


154



Thermal analysis performed on a sample of G-11 under nitrogen atmosphere 

resulted in a series of highly overlapping endothermic and exothermic steps 

(Figure 6.16). The first one consisted in an endothermic process of dehydration 

that started at room temperature and ended below 193 °C resulting in the loss of 

five water molecules [calc (found): 4.21% (4.22%)]. Immediately a second, 

exothermic step composed of several overlapping sub-steps resulted in the loss 

of the guanidinium cation together with the ethyl groups below 688 °C, above 

this temperature no important change of mass is evident suggesting the 

formation of an inorganic stable phase. Interestingly, the thermal stability of 

G-11 is similar to that of the dimethyltin isostructural species reported by 

Reinoso 13 while in that case after the organic groups were lost the stable phase 

was found at 620 °C; therefore we conclude that G-11 remains stable for a longer 

temperature span. 


155



Single crystal XRD revealed that 11 crystallize in the monoclinic I 2/a space group. 

The polyanionic building block in 11 (Figure 6.17) is composed of two (C 2 H 5 )Sn 2+ 

groups covalently attached to a novel hexatungstate [W 6 O 22 ] 8- isopolyanion 

recently discovered by Reinoso et al. 13 which constructs a 1-dimensional chain 

via (W=)O-Sn-O(=W´) bridges. The building block in 11 has a C i symmetry 

providing that the ethyl groups can rotate freely. 


[{Sn(C 2 H 5 ) 2 } 2 (W 6 O 22 )] 4- building block. Colour code: WO 6 octahedra: dark teal; tin: 

olive green; carbon: black; oxygen: red; hydrogen: light gray. 

The (W 6 O 22 ) 8- fragment in 11 can be described as two fused W 3 O 13 trimers linked 

via edge sharing of WO 6 octahedra. The tungsten-oxygen bond lengths in 11 are 

not unusual for isopolytungstates, and in this particular case they are very 

similar of those that Reinoso found for his dimethyltin derivative. 13 This 

hexatungstate fragment is stabilized by two (C 2 H 5 ) 2 Sn 2+ groups and the use of 

[C(NH 2 ) 3 ] + cations allowed us to selectively crystallize 11. Our efforts to obtain 

156


this functionalized isopolyanion with any other alkali cation failed, since we 

always obtained salts of paratungstate-B. 

The two (C 2 H 5 ) 2 Sn 2+ moieties in 11 are bound to the hexatungstate fragment via 

the terminal O3B and the bridging O12S atoms (see Figure 6.17). The Sn centers 

are pentacoordinated, and the highly distorted coordination geometry of the cis- 

(C 2 H 5 ) 2 SnO 3 unit is best described as trigonal-bipyramidal. The equatorial plane 

is defined by O3B and the two ethyl groups, whereas O12S is located in an axial 

position. The coordination sphere of Sn1 is completed by a terminal oxygen atom 

(O3T) of an adjacent hexatungstate fragment, consequently occupying the 

remaining axial position. The distortion of the cis-(C 2 H 5 ) 2 SnO 3 unit is reflected by 

the long Sn1-O3T bond [2.267(5) Å] and by the axial O3T-Sn1-O12S and the 

equatorial C1-Sn1-C3 bond angles [168.57(16) and 130.4(3) respectively]. A list 

with a comparison of selected bond distances and angles of polyanion 11 and 

Reinoso´s dimethyltin [{(CH 3 ) 2 Sn} 2 (W 6 O 22 )] 4- analogue is presented in Table 6.5, 

whereas Table 6.6 contains a list with crystallographic data of polyanion 11. 

Table 6.6 Selected Bond Lengths (Å) and Angles (°) of polyanion 11 and 

[{(CH 3 ) 2 Sn} 2 (W 6 O 22 )] 4- (reference 13). 

11 [{(CH 3 ) 2 Sn} 2 (W 6 O 22 )] 4- 

Sn1-O3B 2.021(4) 2.019(7) 

Sn1-O12S 2.185(4) 2.160(8) 

Sn1-O3T 2.267(5) 2.207(4) 

Sn1-C1 2.141(8) 2.111(9) 

Sn1-C3 2.148(9) 2.106(12) 

C1-Sn1-C3 130.4(3) 124.8(4) 

O3T-Sn1-O12S 168.57(16) 160.1(2) 

157


Based on the comparison of bond distances and angles presented in Table 6.5 

between the two analogues, it is evidence at first glance that the main differences 

lie in the angles surrounding the tin atom. The greater size of the ethyl group 

compared to the methyl and therefore their inherent bulkiness account for a 

greater repulsion between ethyl groups as well as the axial oxygen atoms in the 

trigonal bipyramidal geometry of the tin centre; on the other hand, the largest 

Sn1-O3T bond length in comparison to their dimethyltin functionalized 

hexatungstate analogue is also to be expected. 

The crystal packing of G-11 shows that the (W 6 O 22 ) 8- fragments are linked by cis- 

(C 2 H 5 ) 2 SnO 3 moieties, resulting in the 1D hybrid organic-inorganic POM 

assembly (Figure 6.18). Each hexatungstate fragment coordinates four 

(C 2 H 5 ) 2 Sn 2+ groups in such a way that two adjacent (W 6 O 22 ) 8- clusters are 

connected by two cis-(C 2 H 5 ) 2 SnO 3 moieties. 


1-dimensional chain composed of [{Sn(C 2 H 5 ) 2 } 2 (W 6 O 22 )] 4- building blocks. The 

colour code is the same as in Figure 6.17. 

158



G-11 

Formula C 12 H 54 N 12 O 27 Sn 2 W 6 

Mol. Wt. 

(g/mol) 

2139.08 


Crystal size 

(mm) 


Space group 

(Nr.) 

colourless 

0.17 x 0.15 x 0.13 

monoclinic 

15 

a (Ǻ) 20.4755(4) 

b (Ǻ) 10.07520(10) 

c (Ǻ) 20.5352(2) 

β (°) 103.2770(10) 

Volume (Ǻ 3 ) 4123.07(10) 

Z 4 

D calcd (g/cm 3 ) 3.359 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

17.948 

196352 

7541 

6059 

0.0332 

0.0930 

GoF 1.046 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

159



In this chapter a variety of 1-dimensional architectures functionalized with 

diethyltin linking the polyoxotungstate unit blocks was presented, even when all 

of them were obtained by systematic crystallization with guanidinium as 

counter-cation, the diversity of the arrangements is nonetheless very rich, having 

in fact the only isopolyoxotungstate reported in this work, namely polyanion 11 

a 1-D assembly in the solid state. 

Polyanions 7 and 8 represent the first diethyltin functionalized 

polyoxotungstates with arsenic (III) and antimony (III) as heteroatoms in an 

unprecedent type of linkage thus forming a dimmer as a building unit which 

links further units in a 1-dimensional assembly in the solid state where two out 

of the three tin atoms are hexacoordinated to four oxygen and two ethyl groups 

and one is pentacoordinated to three oxygen and two ethyl groups, being the 

latter the one that does not participate in further bonding with other units. 

Presumably the dimmer would not survive as a unit in solution but half of it, 

since the bonding between both units seems to be not strong enough due to its 

great value of 2.441(7) Ǻ. 

Polyanion 9, on the other hand, composed of a trivacant Keggin of the type B-β 

with arsenic (III) as heteroatom and three diethyltin moieties, two of them 

pentacoordinated and the other one hexacoordinated, represents another novel 

1-dimensional architecture connecting each building units in a zig-zag fashion 

through both pentacoordinated tin atoms, opposite as polyanions 7 and 8, where 

the connectivity to neighbouring units was made by means of the 

hexacoordinated tin atoms. 

160


Completely different from the above mentioned structures, polyanion 10 was not 

obtained based on trilacunary Keggin precursors, but from the monovacant 

[P 2 W 20 O 70 K(H 2 O) 2 ] 10- (P 2 W 20 ) polyoxophosphotungstate, which can be considered 

as a tetradentate ligand in the vacant site, which was occupied by two 

dimethyltin moieties resulting in the first organotin functionalized 1-dimensional 

polyanion based on P 2 W 20 . 

Lastly, the only isopolytungstate reported in this work was the analogue of that 

synthesized by Reinoso et al. in 2006 13 now with diethyltin moieties as linkers to 

the novel [W 6 O 22 ] 8- unit. It was proved that the longer arms of the ethyl groups 

played no role in the connectivity and overall arrangement of polyanion 11 in 

comparison to its dimethyltin analogue, therefore adding a second member to 

the family of compounds containing the early unprecedented [W 6 O 22 ] 8- unit. 

In summary, the role of the guanidinium cation as crystallizing agent proved a 

vast versatility in terms of the different arrangements in which the compounds 

described in this chapter were obtained in the solid state, even more remarkable 

is the fact that polyanions 7 to 9 are basically based on the same trivacant B-β 

Keggin unit, but from the point of view of connectivity, the coordination number 

of tin played the major role on the way the structure crystallized, i.e. how the 

building units connected to each other. From the experimental point of view 

(reaction conditions), is the pH value the main factor to be considered, since in all 

cases the reaction time as well as the temperature were similar. 

161



(1) a) Bareyt, S.; Piligkos, S.; Hasenknopf, B.; Gouzerh, P.; Lacôte, E.; 

Thorimbert, S.; Malacria, M. Angew. Chem. 2003, 115, 3526. b) Bareyt, S.; 

Piligkos, S.; Hasenknopf, B.; Gouzerh, P.; Lacôte, E.; Thorimbert, S.; 

Malacria, M. Angew. Chem. Int. Ed. 2003, 42, 3404. 

(2) Kortz, U. ; Savelieff, M. G.; Bassil, B. S.; Dickman, M. H. Angew. Chem. Int. 

Ed. 2001, 40, 3384. 


(4) Bösing, M.; Loose, I.; Pohlmann, H.; Krebs, B. Chem. Eur. J. 1997, 3, 1232. 







(8) Hervé, G.; Tézé, A.; Contant, R. In : Polyoxometalate Molecular Science; 

Borrás-Almenar, J. J., Coronado, E., Müller, A., Pope, M. T., Eds.; Kluwer: 

Dordrecht, The Netherlands, 2003. 


162


(10) Reinoso, S.; Dickman, M. H.; Reicke, M.; Kortz, U. Inorg. Chem. 2006, 45, 

9014. 


(12) a) Tourné, C. M.; Tourné, G. F.; Weakley, T. J. R. J. Chem. Soc., Dalton Trans. 

1986, 2237. b) Tourné, G. F.; Tourné, C. M. In Polyoxometalates: From 

Platonic Solids to Antiretroviral Activity; Pope, M. T., Müller, A., Eds.; 

Kluwer: Dordrecht, The Netherlands, 1994.; pp 59-70. c) Tourné, C. M.; 

Tourné, G. F. J. Chem. Soc., Dalton Trans. 1988, 2411. d) Maksimovskaya, 

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163

Chapter VII. Discrete Molecular Assemblies of Diorganotin Functionalized Heteropolytungstates 

Chapter VII. Discrete Molecular Assemblies of Diethyltin 


7.1 The Diethyltin Functionalized Eicosatungstodiphosphate 

Polyanion: [{Sn(C2H5)2(H2O)2}(P2W20O70K(H2O)2)] 7- 

The novel monosubstituted eicosatungstodiphosphate polyanion: 

[C(NH 2 ) 3 ] 7 [{Sn(C 2 H 5 ) 2 (H 2 O) 2 }P 2 W 20 O 70 K(H 2 O) 2 ]·13H 2 O 

(G-12) 

Represent the first discrete functionalized polyoxotungstate with the diethyltin 

electrophile based on the monovacant [P 2 W 20 O 70 (H 2 O) 2 ] 10- (P 2 W 20 ) polyanion and 

is from the structural point of view similar to the dimethyltin functionalized 

eicosatungstodiphosphate polyanion 10 described in Chapter VI (see 6.3 The 

Dimethyltin Functionalized Eicosatungstodiphosphate Polyanion: 

[{Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 K(H 2 O) 2 )] 5- ). Nevertheless, the bigger size of the ethyl 

in comparison to the methyl group resulted in important differences in terms of 

structural features. 

Polyanion 12 can be synthesized by two different methods, i.e. with the 

potassium salt of the eicosatungstodiphosphate (P 2 W 20 ) polyanion or with the 

potassium salt of the monolacunary [A-α-PW 11 O 39 ] Keggin polyanion in 

stoichiometric quantities. In both cases 12 crystallizes as a guanidinium salt. 

164



Method 1. 0.500 g (0.087 mmol) of K 10 [P 2 W 20 O 69 K(H 2 O) 2 ]· 24H 2 O were added to 

an aqueous (25 mL) solution of 0.026 g (0.105 mmol) of (C 2 H 5 ) 2 SnCl 2 upon 

stirring; following complete dissolution the pH was adjusted to 3.0 with 1 M HCl 

and the mixture was stirred for another 60 min. at 40°C, then the solution was 

left for a few minutes to cool down to room temperature and 0.5 mL of 

C(NH 2 ) 3 Cl 1M were added to the reaction mixture, afterwards the mixture was 

filtrated. Slow evaporation at room temperature led to a crystalline colourless 

material (Yield: 0.12 gr, 23% based on W) from which a suitable single crystal 

was choose to perform a crystallographic measurement. IR ν max /cm -1 : 1454 (w), 

1415 (w), 1379 (w), 1228 (w) 1192 (w), 1089 (s), 1072 (s), 1018 (m), 953 (s), 921 (s), 

858 (m), 789 (w), 746 (w), 683 (w), 648 (sh), 595 (vw), 577 (vw), 519 (m), 443 

(w),413 (w). 

Method 2. 0.560 gr. (0.175 mmol) of K 7 [A-α-PW 11 O 39 ]·14H 2 O were added to an 

aqueous (25 mL) solution of 0.052 gr (0.210 mmol) of (C 2 H 5 ) 2 SnCl 2 while stirring; 

following complete dissolution the pH was adjusted to 2 and the mixture was 

stirred for another hour at 40°C, after the solution cooled down to room 

temperature, 0.5 mL of C(NH 2 ) 3 Cl 1M were added to the reaction mixture and 

subsequently the solution was filtrated. Slow evaporation at room temperature 

led to a crystalline colourless material (Yield: 0.14 gr, 27% based on W). The 

infrared spectra correspond exactly to the bulk material obtained by method 1. 

165



The infrared spectra recorded on G-12 (Figure 7.1) confirms the presence of the 

P 2 W 20 unit in agreement to the assignment of Contant 1 ; i.e. asymmetric 

stretching (v as ) P-O frequencies were observed at 1089 and 1072 cm -1 ; as well as 

the W-O t v as bands at 953 and 921 cm -1 . The signals found at 858, 789 and 746 cm - 

1 are assigned to the stretching vibrations of W-O-W bridges. The P-O bend band 

was found at 595 cm -1 . Furthermore, the presence of the diethyltin group 

attached to the P 2 W 20 unit is unambiguously established by the presence of two 

peaks of low intensity at 1228 and 1192 cm -1 characteristic of the bending 

symmetric vibration (δ sy ) of organotin derivatives. 2 Additionally, three signals of 

weak intensity at 1454, 1415 and 1379 cm -1 corresponds to δ sy (CH 3 ) and δ (CH 2 ), 

respectively. 3 Figure 7.1 FT-Infrared Spectrum of compound G-12. 

166



Thermogravimetric analysis (TGA) performed on a sample of G-12 under N 2 

atmosphere (Figure 7.2) revealed an endothermic dehydration step starting at 

room temperature resulting in the release of 13 water molecules below 181°C 

[calc. (found): 4.23% (4.22%)], immediately afterwards, release of the organic 

groups takes place in a series of highly overlapping exothermic steps. Liberation 

of the [C(NH 2 ) 3 ] + cations, namely four of them takes place below 319°C and the 

remaining three below 416°C. Between 416°C and 531°C release of both ethyl 

groups takes place. Decomposition of the metal-oxo framework ends at 

approximately 700°C resulting in a stable inorganic phase containing tin, oxygen 

and tungsten. 


167



Polyanion 12 (Figure 7.3) crystallized as a guanidinium salt in the triclinic space 

group P-1 by reaction of stoichiometric amounts of the potassium salt of the 

monovacant eicosatungstodiphosphate polyanion and diethyltindichloride. As 

explained in the synthetic procedure part, 12 can be also synthesized by reaction 

of two equivalents of [A-α-PW 11 O 39 ] -7 (PW 11 ) with one of diethyltin in aqueous 

acidic medium. As Tourné 4 reported, PW 11 converts to P 2 W 20 by slight 

acidification, therefore formation of 12 and conversion of PW 11 to P 2 W 20 occurs 

perhaps simultaneously in a “self-assembly” fashion. 

Figure 7.3. Combined polyhedral and ball-and-stick representation of 12 (left: 

front view with atom labeling, right: upper view). Colour code: WO 6 polyhedra 

(dark red); balls are potassium (plum), tin (olive green), oxygen (red), carbon 

(black) and hydrogen (white). 

168


Polyanion 12 has C s symmetry, considering the ethyl groups in free rotation and 

is composed of two [A-α-PW 9 O 34 ] (PW 9 ) units bridged by two octahedrally 

coordinated tungsten atoms in the equatorial plane. Each of these two tungsten 

atoms is connected to two edge shared tungsten octahedra from each (PW 9 ) unit 

via four oxygen bridges, leaving two terminal oxygen in the axial position: one 

facing the cavity of the polyanion and one, diprotonated, in the opposite 

direction. 

The vacancy, corresponding to a third octahedrally coordinated tungsten atom in 

the plenary [P 2 W 21 O 71 (H 2 O) 3 ] 6- 5 , is occupied by an hexacoordinated Sn(IV) atom 

in an octahedral fashion, i.e. (C 2 H 5 ) 2 SnO 4 . Tin is bridged to a tungsten from each 

PW 9 unit through two Sn-O-W bridges from two cis equatorial oxygen. In 

addition, the two other oxygen atom in the equatorial position are diprotonated 

and facing outside the polyanion. The protonation was confirmed with Bond 

Valence Sum (BVS) calculations. 6 The ethyl groups are in trans position to each 

other and are situated axially to the oxygen atoms. The cavity of the polyanion is 

occupied by a six coordinated potassium ion bonded to the terminal oxygen of 

the remaining edge shared WO 6 octahedra of the two PW 9 units and to the inner 

terminal oxygen of the two ‘belt’ tungsten. This potassium atom in the P 2 W 20 

polyanion was observed by Tourné 4 and was later confirmed by Maksimovskaya 

et al. 7 Indeed, we observed also the presence of this potassium cation in 

polyanion 10. 

A list of selected bond distances and angles of polyanion 12 as well as a 

comparison with the dimethyltin functionalized analogue polyanion 10 is 

presented in Table 7.1. 

169


Table 7.1 Selected Bond Lengths (Å) and Angles (°) of Polyanions 12 and 10.* 

12 10 

Sn1-O3S1 2.216(9) 2.124(13) 

Sn1-O2S1 2.215(8) 2.183(13) 

Sn1-O1S1 2.316(10) 2.314(15) 

Sn1-O4S1 2.266(10) 2.567(14) 

Sn1-C1S1 2.100(15) 2.100(2) 

Sn1-C3S1 2.117(15) 2.14(2) 

C1S1-Sn1-C3S1 171.5(6) 165.6(9) 

* see Chapter VI: 6.3 The Dimethyltin Functionalized Eicosatungstodiphosphate 

Polyanion: [{Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 K(H 2 O) 2 )] 5- 

From the values depicted in Table 7.1, it is evident at first glance that both bonds 

that connect the tin atom and the terminal oxygen of the P 2 W 20 unit are rather 

larger than those of the dimethyl analogue likely due to steric reasons from the 

ethyl groups. The tin-oxygen bond that connects further P 2 W 20 units in polyanion 

10 is fairly larger than the equivalent in 12, which is diprotonated, whereas the 

tin-carbon lengths are similar for both polyanions, the C-Sn-C angle in 12 is 

slightly wider, as expected for a bulkier group. 

Further crystallographic information is presented in Table 7.2 

170



G-12 

Formula C 11 H 86 KN 21 O 87 P 2 SnW 20 

Mol. Wt. 

(g/mol) 

5801.74 


Crystal size 

(mm) 


Space group 

(Nr.) 

colourless 

0.29 x 0.13 x 0.10 

triclinic 

a (Ǻ) 15.3713(4) 

b (Ǻ) 16.6713(4) 

c (Ǻ) 19.8403(6) 

α (°) 88.192(2) 

β (°) 89.360(2) 

γ (°) 73.8770(10) 

Volume (Ǻ 3 ) 4881.8(2) 

Z 2 

D calcd (g/cm 3 ) 3.947 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

2 

23.901 

266617 

24892 

18797 

0.0410 

0.1009 

GoF 1.025 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

171


7.2 A Novel Diethyltin Functionalized Dimer Based on the Lone- 

Pair Containing Trivacant Nonatungstoarsenate Keggin Anion: 

[{Sn(C2H5)2(H2O)}3(B-β-AsW9O33)]2 6- 

Reaction of stoichiometric amounts of Na 9 [B-α-AsW 9 O 33 ]· 27H 2 O and 

(C 2 H 5 ) 2 SnCl 2 at acidic, aqueous media, resulted in the discrete dimer: 

[C(NH 2 ) 3 ] 6 [{Sn(C 2 H 5 ) 2 (H 2 O)} 3 (B-β-AsW 9 O 33 )] 2 ·5H 2 O 

(G-13) 

Polyanion 13 is composed of two (B-β-AsW 9 O 33 ) units linked together via four O- 

Sn-O bridges from four six-coordinated tin atoms (C 2 H 5 ) 2 SnO 4 in a distorted 

octahedral geometry. The reaction conditions used to obtain G-13 were very 

similar of those applied for the synthesis of the 1-dimensional species G-9 (see 

Chapter VI: 6.2 A Lone-Pair Polyoxotungstatoarsenate [{Sn(C 2 H 5 ) 2 } 3 (H 2 O) 2 (B-β- 

AsW 9 O 33 )] 3- and its 1-Dimensional Arrangement through Diethyltin Bridges), 

nevertheless, the architecture of 9 in the solid state is completely different from 

that of 13. 

172



0.147 g of (C 2 H 5 ) 2 SnCl 2 (0.593 mmol) were dissolved in 25 mL of water and 

stirred until complete dissolution, afterwards 0.500 g of Na 9 [B-α- 

AsW 9 O 33 ]· 27H 2 O (0.169 mmol) were added to the solution and the pH was 

adjusted to 2.0 with HCl 4 M. After the mixture was left for 60 minutes with 

continuous stirring at 40 °C, filtration followed in order to separate unreacted 

material. 0.4 mL of a 1 M solution of [C(NH 2 ) 3 ]Cl were added to the filtrate and 

after approx. 15 days of slow evaporation at room temperature; good quality, 

colourless crystals adequate for X-ray analysis were obtained. Yield: 0.20 g, 19% 

(based on W). IR ν max /cm -1 : 1454 (m), 1414 (m), 1378 (m), 1233 (w), 1193 (m), 1119 

(sh), 1076 (sh), 1031 (sh), 953 (s), 878 (w), 812 (s), 719 (sh), 687 (sh), 518 (sh), 475 

(w), 425 (sh). 


The signals below 1000 cm -1 are very similar of those recorded for the pure 

Na 9 [B-α-AsW 9 O 33 ]· 27H 2 O precursor 8 , nevertheless shifted to some degree what 

gives evidence of the presence of the polyoxotungstates framework in the sample 

(Figure 7.4). On the other hand, evidence of the existence of the (C 2 H 5 ) 2 Sn 2+ 

moiety in the compound is unequivocally attested by the presence of two signals 

of weak and medium intensity (1233 and 1193 cm -1 , respectively) distinctive of 

the bending symmetric vibration (δ sy ) of organotin derivatives. 2 The three signals 

at 1454, 1414 and 1378 cm -1 of similar (medium) intensity deliver evidence of the 

presence of the ethyl group in the compound, since such peaks are distinctive of 

the bending symmetric (δ sy ) and bending asymmetric (δ as ) of the CH 3 group, and 

δ sy of the CH 2 group. 3 173




Thermogravimetic analysis performed in a sample of G-13 (Figure 7.5) illustrates 

a single, endothermic step that starts at room temperature and ends below 162 °C 

resulting in the loss of 11 hydration molecules [calc (found): 3.23% (3.29%)]. 

Immediately afterwards a series of three exothermic steps results in the release of 

the organic (guanidinium cations as well as the ethyl groups) species below 660 

°C, after no important change of weight is evident, consequently a stable, 

inorganic specie remains unchanged until the end of the measurement at 900 °C. 

174




Polyanion (pa) 13 crystallizes selectively as a guanidinium salt in the P21/n 

monoclinic space group. By comparing the reaction conditions between species 9 

and 13, it becomes evident that the only difference consists in the pH value (3.0 

vs. 2.0, respectively), nevertheless this variation in the pH resulted in important 

differences in terms of the way the polyanion crystallizes; on the other hand, we 

observed isomerization from the α to β (B-AsW 9 O 33 ) species in aqueous, acidic 

medium, phenomena that was also found in the case of pa 9 and in prior work by 

Hussein et al. 9 

As illustrated in Figure 7.6 (with atom labelling), pa 13 consists of two (B-β- 

AsW 9 O 33 ) units whereas their vacant sites are facing to opposite directions and 

are linked together via four O-Sn-O bridges from four hexacoordinated 

175


(C 2 H 5 ) 2 SnO 4 tin atoms. The dimer has C i symmetry whereas the monomer C 1 ; 

provided that the ethyl groups can freely rotate. A third tin (Sn3), different from 

the other two is pentacoordinated with a trigonal bypiramidal geometry, being 

this tin atom the only one that does not participate in the linkage between (B-β- 

AsW 9 O 33 ) units. 


[{Sn(C 2 H 5 ) 2 (H 2 O)} 3 (B-β-AsW 9 O 33 )] 2 6- . Color code: WO 6 octahedra (pale blue); tin 

(olive green), carbon (black), oxygen (red), X (yellow) and hydrogen (light grey). 

All three tin atoms have two ethyl groups attached in trans positions as well as 

one oxygen atom found to be diprotonated according to Bond Valence Sum (BVS) 

calculations 6 performed in the pa. The two hexacoordinated tin atoms are 

connected to the vacant sites of the trilacunary tungstoarsenate Keggin anion via 

two Sn-O bonds to terminal oxygen corresponding to two corner-shared 

octahedra from two neighboring {W 3 O 13 } triads and further links the other (B-β- 

AsW 9 O 33 ) unit via two rather long [2.770(13) and 2.774(13) Ǻ] Sn-O bonds. 

176


The C-Sn-C angles in both hexacoordinated tin angles are very similar [152.6(8) 

and 152.2(9)°] whereas in the case of the pentacoordinated tin atom such angle is 

smaller [133.5(14)°], what is in principle expected due to less repulsion of 

neighbouring atoms what is not the case in the other two tin atoms, i.e. Sn1 and 

Sn2. 


[{Sn(C 2 H 5 ) 2 (H 2 O)} 3 (B-β-AsW 9 O 33 )] 2 6- in a side view (left) and upper view (right). 

The colour code is the same as in Figure 7.6. 

A list of selected bond distances and angles of polyanion 13 are summarized in 

Table 7.3 

177



13 

Sn1-O41S 2.163(13) 

Sn1-O11S 2.047(13) 

Sn1-O6T 2.770(13) 

Sn1-O1S1 2.433(18) 

Sn1-C1S1 2.09(2) 

Sn1-C3S1 2.12(2) 

C1S1-Sn1-C3S1 152.6(8) 

Sn2-O6S2 2.129(12) 

Sn2-O72S 2.076(13) 

Sn2-O4T 2.774(13) 

Sn2-O1S2 2.499(17) 

Sn2-C1S2 2.126(18) 

Sn2-C3S2 2.130(2) 

C1S2-Sn2-C3S2 152.2(9) 

Sn3-O93S 2.025(14) 

Sn3-O13S 2.081(14) 

Sn3-O1S3 2.34(3) 

Sn3-C1S3 2.09(4) 

Sn3-C3S3 2.12(3) 

C1S3-Sn3-C3S3 133.5(14) 

From Table 7.3, it is at first glance evident that the very long bond distances that 

bridge both [{Sn(C 2 H 5 ) 2 (H 2 O)} 3 (B-β-AsW 9 O 33 )] halves would hardly survive in 

solution, on the other hand, the Sn-C bond lengths are not unusual for organotin 

derivatives observed in the present work and in previous investigations (refer to 

178


Chapter III for further details), also the Sn-OH 2 bond distances are common for 

diprotonated oxygen atoms attached to tin. Further crystallographic data of 

compound G-13 is summarized in Table 7.4. 


G-13 


Mol. Wt. 

(g/mol) 

3188.24 


Crystal size 

(mm) 


colourless 

0.20 x 0.13 x 0.12 

monoclinic 

Space group 

14 

(Nr.) 

a (Ǻ) 12.6096(3) 

b (Ǻ) 38.0397(9) 

c (Ǻ) 12.9027(3) 

β 117.3590(10) 

Volume (Ǻ 3 ) 5496.7(2) 

Z 4 

D calcd (g/cm 3 ) 3.853 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

20.804 

138266 

12593 

10231 

0.0595 

0.1644 

GoF 1.077 

a R(F) = Σ||F o | - |F c ||/Σ|F o |; wR(F 2 ) = {Σ[w(F 2 o - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

179


7.3 The Keggin-based Mixed Species [{Sn(C2H5)2(H2O)}(B-α- 

AsW9O33){Sn(C2H5)2(H2O)}2(B-α-AsW9O33)] 12- Diethyltin Containing 

Polyanion 

Reaction of 1 equivalent of K 14 [As 2 W 19 O 67 (H 2 O)] with 3 of (C 2 H 5 ) 2 SnCl 2 in 

aqueous, moderately acidic media resulted in the (B-α-AsW 9 O 33 ) based Keggin 

mixed species: 

[C(NH 2 ) 3 ] 12 [{Sn(C 2 H 5 ) 2 (H 2 O)}(B-α-AsW 9 O 33 ){Sn(C 2 H 5 ) 2 (H 2 O)} 2 (B-α-AsW 9 O 33 )]·7H 2 O 

(G-14) 

As a matter of fact, this reaction was the first effort to graft the (C 2 H 5 ) 2 Sn 2+ 

electrophile in the vacant site of the dilacunary [As 2 W 19 O 67 (H 2 O)] 14- polyanion, 

but opposite as expected, the polyoxotungstodiarsenate broke in two trivacant 

(B-α-AsW 9 O 33 ) halves giving therefore the appropriate docking sites for the 

diethyltin group to attach. Interestingly, the reaction conditions used to obtain 

G-14 were identical of those for G-8 (see Chapter VI: 6.1 The 

[{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-XW 9 O 33 ) 2 ] 6- (X = Sb III , As III ) Lone-Pair Polyoxotungstate 

Dimer and its 1-D Architecture in the Solid State), differing only in the amount of 

equivalents of (C 2 H 5 ) 2 SnCl 2 used, namely 4 vs. 3. Polyanion 14 crystallizes as a 

guanidinium salt in the triclinic space group. 

180



0.500 g (0.095 mmol) of K 14 [As 2 W 19 O 67 (H 2 O)] were added to an aqueous solution 

(25 mL) of 0.059 g (0.237 mmol) of (C 2 H 5 ) 2 SnCl 2 . After complete dissolution, the 

pH of the mixture was adjusted to 5.0 with HCl 0.5 M. The solution was heated 

at 80 °C for 1 hour upon stirring. When the reaction mixture was cooled down to 

room temperature it was filtrated to separate all remains of unreacted material. 

0.3 mL of [C(NH 2 ) 3 ]Cl 1M was added to the mixture. After approx. 21 days, 

colourless block-like crystals suitable for X-ray were obtained by slow 

evaporation at room temperature. Yield: 0.17 g, 31% (based on W). IR ν max /cm -1 : 

1457(w), 1416(w), 1378(w), 1234(w), 1190(m), 1119 (sh), 950(s), 875(m), 804 (m), 

764(sh), 722(w), 695(sh), 666(w), 610(sh), 536(sh), 498(w), 444(w). 


Figure 7.8 illustrates the FT-infrared spectrum recorded on a sample of G-14. The 

medium to strong peaks in the ranges 950 and 800 cm -1 , are associated with the 

antisymmetric stretching vibrations of the As-O and the W-Ot bonds [νas(W-Ot) 

and νas(W-Ot) + νas(As-O), respectively]; the weak bands between 800 and 695 

cm -1 originate from the antisymmetric stretching of the (Sn)W-O-W(Sn) bridges; 

whereas the medium and weak intensity peaks below 540 cm -1 correspond to 

bending vibrations of the centralAsO3 group and the (Sn)W-O-W(Sn) bridges. 10 

181



The presence of the (C 2 H 5 ) 2 Sn 2+ moiety is unequivocally proved by the presence 

of two bands of weak and medium intensity at 1234 and 1290 cm -1 , respectively, 

characteristic of the bending symmetric vibration of organotin derivatives. 2 

Whereas the three signals of similar intensity at 1457, 1416, and 1378 cm -1 

corresponds to the bending symmetric and asymmetric vibration modes of the 

CH 3 and CH 2 organic groups. 3 182



Figure 7.9 illustrates the thermogramm recorded on a sample of G-14. Starting at 

room temperature, the compound experiences a clear single endothermic step 

that results in the loss of seven hydration molecules [calc (found): 2.12% (2.27%)] 

below 100 °C. Interestingly, G-14 remains stable exactly 100 °C before 

experiencing decomposition in a series of exothermic steps, i. e. loss of the 

organic groups (guanidinium cations as well as all three ethyl groups) below 442 

°C followed by destruction of the polyoxotungstate framework around 726 °C. 


183



Polyanion 14 crystallizes as a guanidinium salt in the triclinic P -1 space group 

and it consists of two (B-α-AsW 9 O 33 ) units, one of them with two (C 2 H 5 ) 2 SnO 3 

groups grafted to the nonatungtoarsenate and the other (B-α-AsW 9 O 33 ) unit with 

only one (C 2 H 5 ) 2 SnO 3 moiety (Figure 7.10) and has an overall C 1 symmetry as 

well as each half of the molecule with the condition that the ethyl groups can 

freely rotate. Both nonatungstoarsenate units face each other’s vacant sites, 

nevertheless they are shifted due to the bulkyness of the (C 2 H 5 ) 2 SnO 3 groups and 

there is no interaction between both halves not even by means of weak bonding. 


[{Sn(C 2 H 5 ) 2 (H 2 O)}(B-α-AsW 9 O 33 ){Sn(C 2 H 5 ) 2 (H 2 O)} 2 (B-α-AsW 9 O 33 )] 12- . Colour code: 

WO 6 octahedra, teal; tin, olive green; arsenic, yellow; oxygen, red; carbon, black; 

hydrogen, light grey. 

Sn3 is pentacoordinated comprising a trigonal bypiramidal geometry with both 

ethyl groups in the axial positions and a C1S1-Sn3-C3S3 angle of 129.1(7) °; it is 

also grafted to the nonatungstoarsenate unit via two Sn-O bonds whereas both 

184


terminal oxygen atoms correspond to the same edge-shared {W 3 O 13 } triad. A 

third oxygen, namely O1S3 was found to be diprotonated according to Bond 

Valence Sum (BVS) calculations. 6 The other pentacoordinated tin atom (Sn2) is 

also attached to the (B-α-AsW 9 O 33 ) unit via two tin-oxygen bonds, while in this 

case the terminal oxygen atoms correspond to neighbouring edge-shared triads, 

i.e. corner-shared WO 6 octahedra. The C1S2-Sn2-C3S3 angle is similar to that 

corresponding to Sn3, namely 132.7(6)°. A third oxygen (O1S2) is also 

diprotonated. 

The upper half, corresponding to that containing only one (C 2 H 5 ) 2 SnO 3 group is 

attached to the (B-α-AsW 9 O 33 ) unit the same way as Sn2, namely by two Sn-O 

bonds related to two corner-shared WO 6 octahedra. The C1S1-Sn1-C3S1 angle is 

in comparison to the other two slightly wider, namely 140.8(5) ° and O1S1 is like 

the other both cases diprotonated. A list with selected bond distances and angles 

of polyanion 14 is summarized in Table 7.5. 

Interestingly, both (B-α-AsW 9 O 33 ) units did not experience isomerization from α 

to β, like in G-8. Since the pH value as well as all other reaction conditions were 

the same for both cases, the only difference lie in the equivalents of (C 2 H 5 )Sn 2+ ; 3 

for 14 vs. 4 for 8, therefore the electrophilic nature of the diethyltin ion in 14 was 

only strong enough to break the [[As 2 W 19 O 67 (H 2 O)] 14- polyanion precursor in two 

halves and implant all three (C 2 H 5 )Sn 2+ electrophiles in the vacant sites of both 

nonatungstoarsenate resulting units; whereas in 8, excess of (C 2 H 5 )Sn 2+ 

permitted the connection of both (B-α-AsW 9 O 33 ) units with all their lacunas filled 

with diethyltin moieties. 

185



14 

Sn1-O2S1 2.182(9) 

Sn1-O5S1 2.018(10) 

Sn1-O1S1 2.287(10) 

Sn1-C1S1 2.120(13) 

Sn1-C3S1 2.148(15) 

C1S1-Sn1-C3S1 140.8(5) 

Sn2-O2S2 2.038(9) 

Sn2-O5S2 2.130(10) 

Sn2-O1S2 2.348(10) 

Sn2-C1S2 2.118(17) 

Sn2-C3S2 2.112(14) 

C1S2-Sn2-C3S2 132.7(6) 

Sn3-O2S3 2.047(9) 

Sn3-O3S3 2.182(9) 

Sn3-O1S3 2.288(11) 

C1S3-Sn3-C3S3 129.1(7) 

Table 7.6 includes further crystallographic data of polyanion 14. 

186



G-14 

Formula C 24 H 122 As 2 N 36 O 76 Sn 3 W 18 

Mol. Wt. 

(g/mol) 

5946.52 


Crystal size 

(mm) 


Space group 

(Nr.) 

colourless 

0.39 x 0.22 x 0.01 

triclinic 

a (Ǻ) 13.3050(5) 

b (Ǻ) 19.4258(9) 

c (Ǻ) 20.4266(8) 

α 92.051(2) 

β 91.690(2) 

γ 94.804(2) 

Volume (Ǻ 3 ) 5254.7(4) 

Z 2 

D calcd (g/cm 3 ) 3.534 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

2 

21.031 

334926 

42441 

28160 

0.0692 

0.2134 

GoF 1.026 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

187



Polyanion 12, based on the [P 2 W 20 O 69 K(H 2 O) 2 ] 10- monovacant 

polyoxophosphotungstate, represents the second structure based on the avobe 

mentioned precursor functionalized with a diorganotin electrophile, in this case 

with diethyltin. As expected, the longer arms of the ethyl groups hindered 

linkage of a second diethyltin moiety in the still available vacant site like in the 

case of 10 (see Chapter VI: 6.3 The Dimethyltin Functionalized 

Eicosatungstodiphosphate Polyanion: [{Sn(CH 3 ) 2 (H 2 O)} 2 (P 2 W 20 O 70 K(H 2 O) 2 )] 5- ) as well 

as bonding to other units, therefore the size of the organic group linked to the tin 

atom allows to predict the dimensionality of the final product at least for 

[P 2 W 20 O 69 K(H 2 O) 2 ] 10- based compounds. 

The connectivity of the dimer in polyanion 13, i.e. via four Sn-O bonds leaves 

little room for expecting further bonding to another similar units, like in 7 and 8 

(see Chapter VI: 6.1 The [{Sn(C 2 H 5 ) 2 } 6 (H 2 O) 6 (B-β-XW 9 O 33 ) 2 ] 6- (X = Sb III , As III ) Lone- 

Pair Polyoxotungstate Dimer and its 1-D Architecture in the Solid State) where both 

halves of the dimer are linked together via only two Sn-O bonds. We see again in 

this case different coordination modalities for the tin atoms, i.e. six-coordinated 

tin for those that participate in bonding between halves of the dimer whereas the 

third one is pentacoordinated. Such phenomena was already observed in several 

other structures that constructs 1-dimensional assemblies (see Chapter VI) hence 

directly influencing the overall bonding modality of the polyanion. 

The [As 2 W 19 O 67 (H 2 O)] 14- divacant polyoxoarsenotungstate used as a precursor 

that resulted in polyanion 14 would in theory accept two diethyltin electrophiles 

in the lacunary sites, nevertheless such precursor broke in two halves composed 

of (B-α-AsW 9 O 33 ) units, resulting in potentially six vacant sites [three for each (Bα-AsW 

9 O 33 )] available for attachment. Nevertheless it was only three diethyltin 

188


electrophiles what resulted in the mixed species polyanion 14. It is also rather 

easy to rationalize this result since the vacancy in [As 2 W 19 O 67 (H 2 O)] 14- is wider 

(see Chapter I: 1.2.5.2 The dilacunary [X 2 W 19 O 69 (H 2 O)] n- (X = P V , As III ) polyanion) 

than in the case of [P 2 W 20 O 69 K(H 2 O) 2 ] 10- , whereas the latter used as precursor 

resulted in two diorganotin functionalized compounds with intact 

[P 2 W 20 O 69 K(H 2 O) 2 ] 10- framework. 

189










(5) Tourné, C. M.; Tourné, G. F.; Weakley, T. J. R. J. Chem. Soc., Dalton Trans. 

1986, 2237. 

(6) Brown, I. D.; Altermatt, D. Acta Crystallogr. 1985, B41, 244. 

(7) Maksimovskaya, R.I.; Maksimov, G.R. Inorg. Chem. 2001, 40, 1284. 



(10) San Felices, L.; Vitoria, P.; Gutiérrez-Zorrilla, J. M.; Lezama, L.; 

Reinoso, S. Inorg. Chem. 2006, 45, 7748. 

190

Chapter VIII. The Novel Phenylantimony Containing Polyoxotungstate: [{PhSbOH} 3 (A-α-PW 9 O 34 ) 2 ] 9- 

Chapter VIII. The Novel Phenylantimony Containing 

Polyoxotungstate: [{PhSbOH} 3 (A-α-PW 9 O 34 ) 2 ] 9- 

8.1 General Introduction on Organoantimony Functionalized 

Polyoxometalates 

Opposite to the work done on mono- and diorganotin containing 

polyoxometalates, very little has been done in the realm of the organoantimony- 

POM chemistry. To date, there are no reports on analogous organoantimony 

polyanions. 

In 1994, the group of Krebs 1 reported on the solid state structure of (n- 

Bu 4 N) 2 [(Ph 2 Sb) 2 (μ-O) 2 (μ-WO 4 )] 2 (Figure 8.1), which was obtained by reaction 

between Ph 2Sb Cl 3 and (n-Bu 4 N) 2 [WO 4 ] in acetonitrile followed by slow diffusion 

of diethylether. Such anion consists of two WO 4 octahedra bonded to two 

otahedrally coordinated antimony atoms. In detail the structure contains a fourmembered 

[Sb-O-Sb-O] ring which is capped on both sides by a tetrahedral WO 4 

unit. In addition to two bonds to bridging tungsten ligands and two bonds to 

bridging oxo groups, each antimony atom has two Sb-C bonds to phenyl rings to 

complete a distorted octahedral cis-Ph 2 SbO 4 coordination. The two coordinated 

oxo groups are also in cis configuration to each other 

191


Figure 8.1 Ball-and-stick representation of (n-Bu 4 N) 2 [(Ph 2 Sb) 2 (μ-O) 2 (μ-WO 4 )] 2 . 

A few years before, Liu and co-workers prepared the isostructural molybdenum 

analogue. 2 Recently, Winpenny’s group synthesized a reverse Keggin ion 

comprising 12 PhSb units in the addenda positions and a central MO 4 (M = Mn, 

Zn) tetrahedron (Figure 8.2). 3 This uncommon polyanion was obtained by 

reacting PhSbO 3 H 2 with hydrated manganese (II) acetate in MeCN in the 

presence of pyridine or NEt 3 at 100 °C under solvothermal conditions. Each Sb 

has a phenyl group attached to it, with the result that each Sb is six-coordinate 

but with the positions of the p- and d-block elements reversed; therefore it is a 

reverse Keggin. This creates a position where the d-block metal ion is trapped in 

a tetrahedral coordination environment at the center of the cage. The orientation 

of the triangular Sb units is such that this is the ε-Keggin rather than the more 

common α-isomer. 

192


Figure 8.2 Combined polyhedral / ball-and-stick representation of 

[Mn(PhSb) 12 O 28 {Mn(H 2 O) 3 } 2 {Mn(H 2 O) 2( AcOH)} 2 ] . 

8.2 Organoantimony-Containing Polyoxometalate: 

[{PhSbOH}3(A-α-PW9O34)2] 9- 

Now we report on the synthesis and structural characterization of the 

phenylantimony-containing tungstophosphate 4 : 

Cs 9 [{PhSbOH} 3 (A-α-PW 9 O 34 ) 2 ]· 24H 2 O 

(Cs-15) 

The title polyanion 15 has a dimeric, sandwich-type structure with two {PW 9 } 

Keggin units capping three octahedral {PhSbOH} fragments resulting in an 

assembly with idealized D 3h symmetry. The hydroxo groups all point inside the 

structure and the phenyl groups away from it. Polyanion 15 was isolated as a 

hydrated cesium salt, and was synthesized by hydrothermal conditions. 

193



Method 1. Na 9 [A-α-PW 9 O 34 ]· 7H 2 O (0.750 g, 0.293 mmol) was dissolved in 25 mL 

of a 0.5 M lithium acetate buffer solution at pH 4, whereas 0.17 g (0.444 mmol) of 

Ph 2 SbCl 5 3 was dissolved in a separate beaker in a minimum amount of ethanol. 

Then both solutions were mixed in a beaker, transferred into a hydrothermal 

bomb, and placed in an oven at 140 °C for 5 h. When the solution had cooled 

down to room temperature, it was filtered and layered with a few drops (0.3 mL) 

of 1 M CsCl. Slow evaporation at room temperature led to colourless, rod like 

crystals suitable for XRD measurements after approximately 3 days (yield: 0.19 g, 

19% based on W). IR ν max /cm -1 : 1621 (s), 1479 (m), 1431 (m), 1384 (m), 1088 (s), 

1024 (m), 954 (s), 930 (w), 901 (w), 763 (vs), 691 (w), 664 (w), 614 (w), 524 (m). 

Method 2. K 7 [α-PW 11 O 39 ] · 14H 2 O (0.640 g, 0.203 mmol)) was dissolved in 25 mL 


Ph 2 SbCl 3 was dissolved in a separate beaker in a minimum amount of ethanol. 

Subsequently both solutions were mixed in a beaker, transferred into a 

hydrothermal bomb, and placed in an oven at 140 °C for 5 h. When the solution 

had cooled down to room temperature, it was filtered and a few drops of 1 M 

CsCl (0.3 mL) were added. Slow evaporation at room temperature delivered a 

rod-like crystalline material after 4 days. The FT-IR recorded on a dried sample 

corresponded exactly to that obtained by method 1. 

Method 3. K 10 [P 2 W 20 O 70 (H 2 O) 2 ] · 24H 2 O (1.00 g, 0.175 mmol) was dissolved in 25 

mL of a 0.5 M lithium acetate buffer solution at pH 4, while 0.08 g (0.209 mmol)of 

Ph 2 SbCl 3 was dissolved in a separate beaker in a minimum amount of ethanol. 

Afterwards both mixtures were placed in a beaker and transferred into a 

hydrothermal bomb, which was placed in an oven at 140 °C for 5 h. When the 

reaction mixture had cooled down to room temperature, it was filtered and a few 

drops of 1 M CsCl (0.3 mL) were added. Slow evaporation at room temperature 

194


delivered a rod-like crystalline material after 3 days. The FT-IR recorded on a 

dried sample corresponded exactly to that obtained by method 1. All three 

methods deliver similar yields. 


Fourier transform infrared (FT-IR) spectra recorded on a sample of Cs-15 (Figure 

8.3) showed a weak band at 461 cm -1 , which corresponds to the PhSb 4+ moiety. 6 

The two peaks at 1479 and 1431 cm -1 are assigned to C-C stretching vibrations of 

the aromatic rings, while those found at 894 and 763 cm -1 correspond to aromatic 

C-H out-of-plane vibrations. 7 The bands at 1088 and 1018 cm -1 correspond to the 

P-O antisymmetric stretching modes, whereas the peaks below 1000 cm-1 are 

assigned to terminal W=O as well as bridging W-O-W stretching modes. 8 

Figure 8.3 FT-Infrared Spectrum of compound Cs-15. 

195



Thermogravimetric analysis (TGA) performed on a sample of Cs-15 under a 

nitrogen atmosphere reveals an endothermic dehydration process that starts at 

room temperature and ends below 238°C resulting in a loss of 24 waters of 

crystallization (Figure 8.4). Immediately afterwards, Cs-15 experience gradual 

decomposition confirmed by the series of highly overlapping exothermic steps 

between 240 and 717 °C. Starting at this last temperature, a slight increase in 

mass suggests the formation of a stable inorganic phase that remains almost 

unchanged until the end of the measurement. 

Figure 8.4 Thermogram of compound Cs-15. 

196



The title polyanion 15 has a dimeric, sandwich-type structure with two {PW 9 } 

Keggin units capping three octahedral {PhSbOH} fragments resulting in an 

assembly with idealized D 3h symmetry (Figure 8.5). The hydroxo groups all point 

inside the structure and the phenyl groups away from it. In order to obtain Cs-15, 

hydrothermal conditions needed to be used, and one phenyl group was lost in 

the process. 

Figure 8.5 Combined polyhedral/ball-and-stick representation of 15. 

Colour code: WO 6 octahedra, dark red; antimony, olive green; oxygen, red; 

phosphorus, yellow; carbon, black; hydrogen, gray. 

Cs-15 crystallizes in the monoclinic space group C2/c. Each antimony atom 

exhibits a very regular octahedral coordination with C-Sb-O angles within 7 

degrees of 90 or 180. The axial Sb-OH (trans to phenyl) distances range from 

1.926(15) to 1.935(18) Å, whereas the four equatorial Sb-O bonds are in the range 

of 1.986(12)-2.036(13) Å. Bond Valence Sum (BVS) calculations 9 confirmed that 

197


the axial oxygen atom attached to the antimony is indeed monoprotonated (a list 

with selected bond lengths and angles is presented in Table 8.1). 


15 

Sb1-O1S1 2.026(12) 

Sb1-O2S1 2.036(13) 

Sb1-O3S1 1.935(18) 

Sb1-C1 2.096(16) 

O3S1-Sb1-C1 180.00(2) 

Sb2-O1S2 1.986(12) 

Sb2-O2S2 2.026(13) 

Sb2-O6A 2.000(12) 

Sb2-O7A 2.003(12) 

Sb2-O4S2 1.926(15) 

Sb2-C5 2.140(13) 

O4S2-Sb2-C5 176.7(8) 

Polyanion 15 is structurally related to Pope’s organotin polyanion [(PhSnOH) 3 (Aβ-PW 

9 O 34 ) 2 ] 12- , 10 but there is a charge difference of three units (9- vs. 12-, due to 

Sb 5+ vs. Sn 4+ ) and Pope’s ion contains {A-β-PW 9 } Keggin units rather than {A-α- 

PW 9 } in 15. Considering that we used hydrothermal conditions for the synthesis 

of 15, it is not surprising that any [A-β-PW 9 O 34 ] 9- present was transformed to [Aα-PW 

9 O 34 ] 9- in the course of the reaction. 10,11 Further crystallographic data of 

compound Cs-15 is summarized in Table 8.2. 

198


Table 8.2. Crystallographic Data of Compound Cs-15. 

Cs-15 

Formula C 18 H 58 Cs 9 O 91 P 2 Sb 3 W 18 

Mol. Wt. 

(g/mol) 

6663.32 


Crystal size 

(mm) 


Space group 

(Nr.) 

colourless 

0.35 x 0.13 x 0.01 

monoclinic 

15 

a (Ǻ) 33.899(2) 

b (Ǻ) 13.6814(9) 

c (Ǻ) 21.6122(13) 

β (°) 103.999(3) 

Volume (Ǻ 3 ) 9725.8(11) 

Z 4 

D calcd (g/cm 3 ) 4.551 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

25.479 

181375 

11991 

8338 

0.0592 

0.1741 

GoF 1.027 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

199


8.2.5 Solution Studies (Nuclear Magnetic Resonance) 

After having replaced the Cs+ counterions by Li+ via ion exchange 12 , a series of 

multinuclear magnetic resonance experiment were performed, taking advantage 

of the several NMR active nuclei present in polyanion 15. 

183 W NMR revealed the expected two singlets of relative intensity 1:2 at -115.5 

and -202.9 ppm, respectively (Figure 8.6), confirming the nominal D 3h symmetry 

of 15. 

Figure 8.6 183 W NMR spectrum of 15 in H 2 O/D 2 O medium. 

200


The 31 P NMR spectrum of 15 (Figure 8.7) showed a singlet at -14.7 ppm, whereas 

the 13 C and 1 H NMR spectra are as expected for phenyl groups 7 (Figure 8.8). 

Figure 8.7 31 P NMR spectrum of 15 in H 2 O/D 2 O medium. 

It is of interest to compare the 183 W NMR parameters of 15 with the structurally 

related phenyltin derivatives such as Knoth’s [(PhSnOH) 3 (A-α-PW 9 O 34 ) 2 ] 12- and 

Pope’s [(PhSnOH) 3 (A-β-PW 9 O 34 )2] 12- , [(PhSnOH) 3 (A-α-SiW 9 O 34 ) 2 ] 14- ,and 

[(PhSnOH) 3 (A-β-SiW 9 O 34 ) 2 ] 14- (Table 8.3). 10,11,13 

Table 8.3. Comparison of 183 W NMR Chemical Shifts for 15 and Structurally 

Related Phenyltin Derivatives. 

Polyanion δ cap δ belt δ cap - δ belt Reference 

15 -115.5 -202.9 87.4 4 

[(PhSnOH) 3 (A-α-PW 9 O 34 ) 2 ] 12- -138.6 -190.0 51.4 11 

[(PhSnOH) 3 (A-β-PW 9 O 34 ) 2 ] 12- -123.4 -202.2 78.8 10 

[(PhSnOH) 3 (A-α-SiW 9 O 34 ) 2 ] 14- -150.0 -189.0 39.0 13 

[(PhSnOH) 3 (A-β-SiW 9 O 34 ) 2 ] 14- -126.0 -208.0 82.0 13 

From the data presented in Table 8.3, it is evident that in all cases, the signal for 

the belt tungstens is upfield with respect to the cap tungstens. Also, we can 

201


notice that the chemical shift for the belt tungstens (δ belt ) is always in a narrow 

range of around -190 to -210 ppm, whereas the chemical shift for the cap 

tungstens (δ cap ) ranges from -115 to -150 ppm. This can be explained by the 

presence of α-Keggin vs β-Keggin rotational isomers, which affects the cap 

tungstens more than the belt tungstens. 

Figure 8.8 13 C NMR (left) and 1 H (right) spectra of 15 in H 2 O/D 2 O medium. 

It has been also noticeable that for the phenyltin species the chemical shift 

difference between δ cap and δ belt is consistently larger (~80 ppm) for structures 

containing the β-Keggin isomers than for those with the α -Keggin isomers (40-50 

ppm). On the basis of these NMR parameters, the title polyanion 15 seems to 

follow the trend for the β-Keggin phenyltin isomers, even when it clearly 

contains α -Keggin units. Therefore such phenomena must be due to the presence 

of antimony rather than tin. 

202


8.2.6 Conclusions 

In the present chapter the synthesis and characterization in the solid state as well 

as in solution of the first organoantimony-containing POM was reported. The 

title polyanion 14 can be prepared by the direct interaction of Ph 2 SbCl 3 with three 

different lacunary tungstophospate precursors, namely Na 9 [(A-α-PW 9 O 34 ], 

K 7 [PW 11 O 39 ], or K 10 [P 2 W 20 O 70 (H 2 O) 2 ], in an aqueous acidic medium. 

Hydrothermal conditions were required because of the poor solubility of 

Ph 2 SbCl 3 in water and the need to cleave a phenyl group. Nevertheless, after 

polyanion 15 has been synthesized, it remains stable in the presence of air and 

moisture. In fact, NMR spectra of 15 in aqueous solution remain unchanged for 

weeks. 

The present results likely open the door for a new subfamily of organoantimonycontaining 

polyanions. The well-known monoorganotin POM chemistry has 

been then extended to main group V, and perhaps other RSb analogues of 15 

exist (e.g., R = CH 3 , C 2 H 5 , n-C 4 H 9 , tert-C 4 H 9 , R′COOH, R′COOR′′, R′CONHR′′). 

Furthermore, the entire arsenal of lacunary POM precursors can be reacted with 

Ph 2 SbCl 3 , and the preliminary results in this direction are promising. 

Organoantimony-containing POMs have a smaller charge compared to their 

organotin analogues because of the presence of Sb 5+ vs. Sn 4+ , which could have 

important consequences for their reactivity, stability, toxicity, etc. 

203



(1) Krebs, B. In: Polyoxometalates: From Platonic Solids to Antiretroviral Activity; 

Pope, M. T., Müller, A., Eds.; Kluwer: Dordrecht, The Netherlands, 1994. 

(2) Liu, B.; Ku, Y.; Wang, M.; Wang, B.; Zheng, P. J. Chem. Soc., Chem. Commun. 

1989, 651. 

(3) Baskar, V.; Shanmugam, M.; Helliwell, M.; Teat, S. J.; Winpenny, R. E. P. J. 

Am. Chem. Soc. 2007, 129, 3042. 

(4) Piedra-Garza, L. F.; Dickman, M. H.; Moldovan, O.; Breunig, H. J.; Kortz, 

U. Inorg. Chem. 2009, 48, 411. 

(5) (a) Bertazzi, N. Atti Accad. Sci., Lett. Arti Palermo 1973, 33, 483. (b) Sowerby, 

D. B.; Begley, M. J.; Bamgboye, T. T. J. Organomet. Chem. 1989, 362, 77. (c) 

Rat, C.-I. Ph.D. Thesis, Universität Bremen, Bremen, Germany, 2007. 






(8) Rocchiccioli-Deltcheff, C.; Fournier, M.; Franck, R.; Thouvenot, R. Inorg. 

Chem. 1983, 22, 207. 

(9) Brown, I. D.; Altermatt, D. Acta Crystallogr., Sect. B 1985, 41, 244. 

204


(10) Xin, F.; Pope, M. T. Organometallics 1994, 13, 4881. 

(11) Knoth, W. H.; Domaille, P. J.; Farlee, R. D. Organometallics 1985, 4, 32. 

(12) In order to increase the solubility of Cs-14, ion exchange using a lithium-charged 

resin (Dowex 50W X8 from AppliChem) was performed. 

(13) Xin, F.; Pope, M. T.; Long,G. J.; Russo, U. Inorg. Chem. 1996, 35, 1207. 

205

Chapter IX. Structures without Organometallic Moieties attached to the POM Framework 

Chapter IX. Structures without Organometallic Moieties 

attached to the POM Framework 

During the almost three years of investigating the entire arsenal of vacant 

polyoxometalate towards organotin and –antimony electrophiles, only a very 

small fraction of the reactions made delivered the desired results, i.e. with 

organotin or –antimony moieties grafted to polyoxometalate frameworks, such 

are the compounds described from Chapter IV to VIII. 

Nevertheless, several somewhat interesting (and unexpected) results were found 

in the course of hundreds of reactions that were made throughout the countless 

hours spent in the laboratory during this research. After a given try-out was 

made and solid material was obtained, very often well-known species such as 

Keggin polyanions or B-paratungstate were found after comparing infrared 

measurements or even a short XRD run when the FT-IR results were 

inconclusive, but far from signifying such results a defeat, it was exactly the 

opposite providing even more motivation to keep looking for the right reaction 

conditions that would bring the looked-for results. Not rarely encountering such 

well-known species within a given spectrum of reaction conditions forced us to 

radically change our way of thinking and to try something completely new, like 

the case of compound Cs-15 (Chapter VIII), the only one obtained in 

hydrothermal conditions, and consequently different of all other previous 

compounds reported. 

In the following sections, two novel (to the best of our knowledge) structures will 

be briefly described giving special attention to their structural features. All of 

them were characterized by single crystal X-ray diffraction. 

206


9.1 The Chiral Sandwich-Type [Sb3 III (A-α-PW9O34)] 9- Lone-Pair 

containing Polyanion 

Starting from the Keggin trivacant [PW 9 O 34 ] 9- polyanion, Knoth et al. have 

isolated M 3 (A-α-PW 9 O 34 ) 2 sandwich-type complexes, including heterosubstituted 

compounds M’M”M”’(A-α-PW 9 O 34 ) 2 with a wide range of divalent 3-d transition 

metals, i.e. Co, Mn, Fe, Ni, Cu, Zn and Pd from the 4-d block. 1,2 Numerous 

examples of transition metal atoms sandwiched between (A-α-XW 9 O 34 ) or (B-α- 

XW 9 O 33 ) ( X = As III , Sb III , Bi III , Si IV ) have been prepared. 3 

In 1996, Pope reported a polyanion with three Sn(II) atoms sandwiched between 

two [PW 9 O 34 ] units. 4 Each tin atom has a lone pair directed toward the centre of 

the anion and is connected to two terminal oxygen (from two edge-shared WO 6 

octahedra) from each [PW 9 O 34 ] units. Due to the inequality of the equatorial and 

axial Sn-O bond lengths, one [PW 9 O 34 ] unit is slightly rotated with respect to the 

other [PW 9 O 34 ] unit. Now we report on the analogue chiral sandwich-type with 

antimony (III) atoms instead of tin (II). 

This interesting chiral polyanion composed of two (A-α-PW 9 O 34 ) units 

sandwiched with three Sb (III) atoms was obtained during the series of reactions 

made with hydrothermal conditions between the trivacant (A-α-PW 9 O 34 ) 9- Keggin 

polyanion and the Ph 2 Sb 3+ electrophile. 

As described in Chapter VIII: The Novel Phenylantimony Containing 

Polyoxotungstate: [{PhSbOH} 3 (A-α-PW 9 O 34 ) 2 ] 9- ,the title polyanion (pa) 15 contains 

three (PhSbOH) groups between each (A-α-PW 9 O 34 ) unit, where one phenyl 

group was lost likely because the rather tough reactions conditions, therefore we 

tried to reproduce 15 but instead of adding a few drops of CsCl 1 M as a 

precipitating agent we choose to use in this case PhMe 3 NBr (also an aqueous 

solution at the same concentration). To our surprise, not only a phenyl group 

207


from the Ph 2 SbCl 3 precursor was lost, but the two of them and the antimony 

atom experienced a reduction process from Sb(V) to Sb(III), resulting in the chiral 

sandwich-type polyanion: 

[PhMe 3 N]Na 8 [Sb 3 

III (A-α-PW 9 O 34 ) 2 ] · 17H 2 O 

(PMNa-16) 

Compound PMNa-16 was synthesized by three different methods; the first one 

already mentioned with Ph 2 SbCl 3 as source of Sb, and the last two in a more 

rational way with SbCl 3 and Sb 2 O 3 , respectively. All three methods delivered 

exactly the same result with little difference in the obtained yield. 


Method 1. Na 9 [A-α-PW 9 O 34 ]· 7H 2 O (0.750 g, 0.293 mmol) was dissolved in 25 mL 


Ph 2 SbCl 5 3 was dissolved in a separate beaker in a minimum amount of ethanol. 

Then both solutions were mixed in a beaker, transferred into a hydrothermal 

bomb, and placed in an oven at 140 °C for 5 h. When the solution had cooled 

down to room temperature, it was filtered and layered with a few drops (0.4 mL) 

of 1 M PhMe 3 NBr. Slow evaporation at room temperature led to colourless, block 

like crystals suitable for XRD measurements after approximately 15 days (yield: 

0.32 g, 32% based on W). IR ν max /cm -1 : 1486 (m), 1457 (m), 1408 (w), 1297 (w), 

1232 (w), 1199 (w), 1085 (s), 1035 (m), 949 (s), 892 (m), 811 (m), 784 (s), 688 (w), 

668 (w), 594 (w), 575 (w), 553 (w), 517 (m), 456 (w), 424 (w). 

208


Method 2. SbCl 3 (0.074 g, 0.322 mmol) was dissolved in 25 mL of a 0.5 M lithium 

acetate buffer solution at pH 5. After complete dissolution Na 9 [A-α- 

PW 9 O 34 ]· 7H 2 O (0.500 g, 0.195 mmol) was added and the solution was heated at 

80 °C for 60 minutes upon stirring. After cooling to room temperature the 

reaction mixture was filtrated to separate any unreacted material and 0.5 mL of 

PhMe3NBr 1M was added upon stirring. Slow evaporation at room temperature 

resulted in suitable crystals for XRD measurements after approx. 10 days. (yield: 

0.21 g, 22% based on W). 

Method 3. The same procedure was used as in method 2, but with Sb 2 O 3 (0.114 g 

(0.390 mmol) instead of SbCl 3 . (yield: 0.18 g, 20% based on W). 


Figure 9.1 illustrates the FT-IR spectrum recorded on a sample of PMNa-16 (blue) 

together with the spectrum of the Na 9 [A-α-PW 9 O 34 ]· 7H 2 O precursor (red). The 

series of bands below 1000 cm -1 corresponds to the polyoxotungstophosphate 

framework, whereas the strong signal at 1085 cm -1 shows clear evidence of the 

stretching asymmetric (v a ) P-O band present in all polyoxotungstophosphates. 6 

Within the POM framework is evident a degree of shifting in several peaks; on 

the other hand, several signals of medium and low intensity (i.e. 1408, 1297, 1232 

as well as 1299 cm -1 ) corresponds to the stretching vibration of the C-N bonds. 

The band at 1457 cm -1 is assigned to the bending asymmetric vibration of CH 3 

groups, while the one at 1486 cm -1 matches the typical signal of the aromatic C-C 

bonds. 7 209


Figure 9.1 FT-Infrared Spectra of compounds PMNa-16 (blue) and the 

Na 9 [A-α-PW 9 O 34 ]· 7H 2 O precursor (red). 


A sample of PMNa-16 was studies for its thermo-gravimetrical properties and it 

was found that starting at room temperature a single, endothermic dehydration 

step took place resulting in the liberation of 17 water molecules below 207 °C 

[calc (found): 5.62% (5.61%)]. Immediately afterwards a rather slow exothermic 

step takes place ending below 317 °C and just before that step within a few 

degrees Celsius an abrupt exothermic step is confirmed accompanied with the 

complete destruction of the polyanion as well as the counter-cations; first in a 

sub-step below 539 °C and immediately afterwards with a continuous loose of 

mass until the end of the measurement at 900 °C, as illustrated in Figure 9.2. 

210


Figure 9.2 Thermogram of compound PMNa-16. 


PMNa-16 crystallizes in the R 3 rombohedral space group as a salt with mixed 

PhMe 3 N and Na counter-cations. The structure of 16 (Figure 9.3) consists of two 

[A-α-PW 9 O 34 ] units linked by three Sb(III) atoms resulting in an overall D 3 

symmetry. Close observation of polyanion 16 reveals that one [A-α-PW 9 O 34 ] unit 

is slightly rotated around the C 3 axis from the eclipsed position. 

211


Figure 9.3 Combined polyhedral/ball-and-stick representation of 16. 

Colour code: WO 6 octahedra, light green; antimony, olive green. 

Each Sb (III) is coordinated by two oxygen atoms from two edge-sharing WO 6 

octahedra of each [A-α-PW 9 O 34 ] unit. Each antimony atom has a distorted 

trigonal bipyramidal coordination with two long axial Sb-O bonds [Sb1-O1S1, 

2.219(16) Å; Sb1-O4S1, 2.211(18) Å], two short equatorial Sb-O bonds [Sb1-O2S1, 

1.985(17) Å; Sb1-O3S1, 1.982(16)] and a third “equatorial position” occupied by 

the lone pair of electrons pointing towards the anion’s C 3 axis. A list of selected 

bond lengths and angles of polyanion (pa) 16 and its analogue with Sn(II) 4 is 

summarized in Table 9.1. 

212


Table 9.1 Selected Bond Lengths (Å) and Angles (°) of Polyanions 16 and 

[Sn II 3(A-α-PW 9 O 34 ) 2 ] 12- . * 

X = Sb III ,Sn II 16 [Sn II 3(A-α-PW 9 O 34 ) 2 ] 12- 

X-O (long) 2.22 2.35 

X-O (short) 1.99 2.11 

W-O(X) X-O (long) 1.82 1.82 

W-O(X) X-O (short) 1.91 1.87 

O-X-O (axial) 154.1 141.4 

O-X-O (equatorial) 96.6 97.2 

* Only average values presented. 

The differences in the bond distances, specially regarding the X-O (X = Sb III , Sn II ) 

account for the different charge of both antimony and tin atoms, whereas the 

smallest discrepancies are found between the W-O(X) distances indicating that 

the [A-α-PW 9 O 34 ] units are only affected by the degree of rotation respect to each 

other. 

Further crystallographic data of PMNa-16 is summarized in table 9.2. 

213


Table 9.2. Crystallographic Data of Compound PMNa-16. 

PMNa-16 

Formula C 9 H 48 NNa 8 O 85 P 2 Sb 3 W 18 

Mol. Wt. 

(g/mol) 

5450.70 


Crystal size 

(mm) 


Space group 

(Nr.) 

colourless 

0.39 x 0.33 x 0.19 

rombohedral 

146 

a (Ǻ) 23.4041(11) 

c (Ǻ) 18.9534(11) 

Volume (Ǻ 3 ) 8990.9(8) 

Z 3 

D calcd (g/cm 3 ) 2.969 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

17.965 

90449 

8164 

6203 

0.0592 

0.1931 

GoF 1.275 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

214


9.2 A Novel [H3Se2W22O74(H2O)7] 5- Plenary 

Polyoxodiselenotungstate 

This structure was found in the course of a series of reactions made with sodium 

tungstate dehydrated and selenious acid towards diethyltindichloride aiming to 

obtain a selenium-containing polyoxotungstate functionalized with the 

(C 2 H 5 ) 2 Sn 2+ electrophile since different to other phosphorous- or arsenic- (to 

name just two examples) containing lacunary polyoxotungstates, no such vacant 

POMs (like Keggin or Wells-Dawson) are available with selenium as heteroatom 

to the best of our knowledge. 

Krebs et al. 8 reported in 1994 a molybdate with a SeO 3 unit bonded to the 

Mo 4 O 13 ring with the unshared electron pair occupying the free tetrahedral 

vertex, namely in the [OSeMo 4 O 14 (OH)] 3- polyanion. In order to obtain such 

compound, SeO 2 was reacted with (n-Bu 4 N) 2 [Mo 2 O 7 ] in acetonitrile with 

subsequent diethylether diffusion. Based on Krebs experiment, we decided to 

react Na 2 WO 4·2H 2 O (which is a very common precursor in the synthesis of isoand 

heteropolytungstates, (see Chapter II. Analytical Techniques used in the 

Characterization of POMs and Synthesis of Precursors) with H 2 SeO 3 (selenium 

containing acid as heteroatom) and (C 2 H 5 ) 2 SnCl 2 in aqueous, acidic media. We 

selected such precursors based on their solubility in water, nevertheless the 

compound obtained was a plenary polyoxodiselenotungstate part of it 

resembling the constitution of [P 2 W 20 O 70 ] with a “bridge” of six WO 6 octahedra 

linking both {W 3 O 13 } cap triads, namely: 

Cs 5 [H 3 Se 2 W 22 O 74 (H 2 O) 7 ] · nH 2 O 

(Cs-17) 

215



Na 2 WO 4·2H 2 O (0.887 g, 2.691 mmol) was mixed with H 2 SeO 3 (0.035 g, 0.269 

mmol) and (C 2 H 5 ) 2 SnCl 2 (0.200 g, 0.807 mmol) in 25 mL of water. After complete 

dissolution of all reactants the pH was adjusted to 1.0 with HCl 4 M and heated 

to 80 °C upon stirring for 60 minutes. After completion of reaction, the lukewarm 

solution was filtrated in order to separate any unreacted material and 0.5 mL 

CsCl 1 M was added. Slow evaporation at room temperature resulted in yellow, 

block-like crystals from which XRD experiments were conducted. It was 

necessary to test several single crystals since most of them did not diffracted well, 

eventually it was possible to find a suitable one, which was measured and 

refined. (yield: 0.11 g, 5% based on W). IR ν max /cm -1 : 1159 (w), 1112 (w), 966 (m), 

865 (w), 822 (sh), 746 (m), 674 (w), 500 (w), 456 (w), 440 (w), 421 (w). 


A sample of Cs-17 was used to record its FT-IR spectrum which is illustrated in 

Figure 9.4. As expected, the series of signals below 1000 cm -1 are attributed to the 

polyoxotungstate framework, i.e. W=O stretching modes as well as the stretching 

W-O-W bridges between corner- and edge-sharing octahedra. 9 216


Figure 9.4 FT-Infrared Spectrum of compound Cs-17. 


Polyanion 17 was obtained as a caesium salt corresponding to the P21/c 

monoclinic space group with C 2v symmetry. It consists of a closed structure 

composed of 22 WO 6 octahedra and two selenium atoms as the heteroatoms that 

resembles partially the arrangement of the [P 2 W 21 O 71 (H 2 O) 3 ] 

polyoxodiphosphotungstate. Nevertheless two WO 6 octahedra corresponding to 

the belt [SeW 9 O 34 ] are corner shared instead of edge-shared, which can be 

explained based on the fact that selenium is three and not four-coordinated to the 

Keggin. Therefore the lone-pair of electrons is directed towards the cornershared 

WO 6 octahedra. 

All four corner-shared octahedra are linked together via another two cornershared 

WO6 where only one WO 6 octahedron would complete the 

[P 2 W 21 O 71 (H 2 O) 3 ] structure, hence shaping a kind of “bridge”, as depicted in 

Figure 9.5. 

217


a) b) 

Figure 9.5 Combined polyhedral and ball-and-stick representation of 17. a) front 

view, b) side view. Yellow balls represent Se. Dark teal octahedra represents 

WO 6 and corresponds to the [P 2 W 21 O 71 (H 2 O) 3 ] framework, whereas the dark red 

octahedra corresponds to the novel “bridge-like” corner-shared WO 6 . 

Bond Valence Sum 10 (BVS) calculations performed on polyanion 17 revealed 

three protons likely to be delocalized through the entire polyanion, as well as 

seven terminal oxygens found to be diprotonated, what accounts for distortion in 

some octahedra. 

Despite multiple efforts to reproduce Cs-17 both by the same original synthetic 

procedure (even when apparently diethyltindichloride does not appear in the 

structure) and more rational paths, it was not possible to obtain the desired 

results, therefore no thermogravimetric studies were possible to conduct. 

A summary of the crystallographic data of Cs-17 is presented in Table 9.3 

218


Table 9.3. Crystallographic Data of Compound Cs-17. 

Cs-17 

Formula H 17 Cs 5 O 81 Se 2 W 22 

Mol. Wt. 

(g/mol) 

6180.01 


Crystal size 

(mm) 


Space group 

(Nr.) 

colourless 

0.41 x 0.33 x 0.19 

monoclinic 

14 

a (Ǻ) 22.3598(18) 

b (Ǻ) 20.2714(14) 

c (Ǻ) 23.886(2) 

β (°) 115.378(4) 

Volume (Ǻ 3 ) 9782.1(13) 

Z 4 

D calcd (g/cm 3 ) 2.666 


(mm -1 ) 


measured 

Reflections 

(unique) 

Reflections 

(obsd.) > 2σ 

R(F) a (obsd. 

reflns) 

wR(F 2 ) a 

(all reflns) 

13.583 

402700 

20035 

11001 

0.1319 

0.3626 

GoF 1.923 


2 - F c2 ) 2 ]/Σ[w(F o2 ) 2 ]} 1/2 . 

219



The resulting polyanions 16 and 17 presents remarkable characteristics even 

when no organometallic moiety was incorporated on the POM framework. 

Chiral configuration in POMs is highly desirable since much biological activity is 

expected to depend on the chiral configuration when potential medicinal 

applications are in mind. We successfully attached three antimony (III) atoms 

sandwiched between two slightly twisted [A-α-PW 9 O 34 ] units resulting in the 

analogous chiral structure synthesized by Pope et al. with tin (II) between two 

[A-α-XW 9 O 34 ] (X = P V , Si IV ). Additionally, we also proved that the same product 

can be obtained by starting with SbCl 3 or Sb 2 O 3 in aqueous, slightly acidic media. 

Polyanion 17 represents a new class of plenary polyoxotungstate with selenium 

(IV) as the heteroatom constructing a framework that resembles that of the 

[P 2 W 21 O 71 (H 2 O) 3 ] polyoxodiphosphotungstate but instead of two edge-shared 

WO 6 octahedra that would complete the [A-α-XW 9 O 34 ] unit, three groups of 

corner-shared WO 6 octahedra link both cap {W 3 O 13 } triads in both extremes of 

the structure in an arched “bridge-like” fashion. Unfortunately, all efforts to 

reproduce this compound were unsuccessful even by modification of several 

parameters such as pH, temperature and ratio of reactants. 

220



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222

Luis Fernando Piedra-Garza - Jacobs University

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