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Fig. 1.10: Schematic representation of the formation of Keggin- and Wells-Dawson type lacunary species in tungsto-phosphate system with respect to pH.Courtesy: Dr. Santiago C. Reinoso a cesium counterion. On the other hand, a series of heteropolyanions can be obtained which has no equivalent in silico-tungstate system. Thus, when the trivacant species A-α-[PW 9 O 34 ] 9− is acidified in excess of potassium counterion, instead of the Keggin ion formation, association of two trivacant species takes place by means of a bridging tungsten in the belt. If the pH is decreased different heteropolyanions are obtained, 13
[P 2 W 19 O 68 (HO)] 14− , [P 2 W 20 O 70 (H 2 O) 2 ] 6− and [P 2 W 21 O 71 (HO) 3 ] 6− , which show one, two and three {WO(HO)} 4+ groups in the central belt, respectively. In addition, when a solution of tungstate is acidified until pH below 2 in the presence of an excess of phosphate, mixture of α and β-isomers of the Wells-Dawson [P 2 W 18 O 62 ] 6− heteropolyanion is obtained instead of the Keggin. The Wells-Dawson heteropolyanion shows a similar behaviour to that of the Keggin, since the basicity of its dissolution produces hydrolytic cleavage of the M-O bonds to give rise to monovacant [P 2 W 17 O 61 ] 10− lacunary species, only if the pH is in between 4 and 6, and to the trilacunary [P 2 W 15 O 56 ] 12− at pH around 10. These trivacant species undergo irreversible processes of transformation to form the hexa lacunary species [P 2 W 12 O 48 ] 14− . Lacunary anions with more than one surface ‘vacancy’ may also be derivatized by cation complexation. Reaction of a stable, lacunary polyoxometalate with transition metal ions usually leads to a product with the unchanged heteropolyanion framework. Depending upon the coordination requirement and the size of a given transition metal ion, the geometry of the reaction product can therefore often be predicted. At the same time it must be pointed out that the mechanism of formation of polyoxometales is not well understood and commonly described as self assembly. Therefore, the synthesis of polyoxoanions with novel shapes and sizes is a very difficult task. But, according to Müller and Pope, POM structure are governed by two general principles. •Polyanions are generated by linking MO n polyhedra via corners and edges leading to different types of faces on the surfaces. •Each metal atom forms an MO n coordination polyhedron (most commonly an octahedron or a square pyramid) in which the metal atoms are displaced, as a result of M-Oπ bonding, towards the terminal polyhedral vertices forming the surface of the structure. Transition metal substituted polyoxometales can also be of interest owing to their magnetic properties. Structures which contain more than one paramagnetic transition metal ion in close proximity may exhibit exchange-coupled spins leading to large spin ground states [36, 37]. The polyoxometalate matrix may be considered as a diamagnetic host encapsulating and thereby isolating a magnetic cluster of transition metals. Polyoxometalate chemistry has received a great research interest in the area of oxidation catalysis 14
Page 1 and 2: Hybrid Organic-Inorganic Polyoxomet
Page 3 and 4: Abstract Polyoxometalates (POMs) ar
Page 5 and 6: the cubic system (space group I m¯
Page 7 and 8: AsW 9 O 32 OH) 2 ]·36H 2 O (RbNa-1
Page 9 and 10: Paris-Sud, Orsay Cedex, France) for
Page 11 and 12: 2.2.9 Synthesis of K 12 [H 2 P 2 W
Page 13 and 14: Bibliography . . . . . . . . . . .
Page 15 and 16: 3.5 Left: combined polyhedral and b
Page 17 and 18: 3.33 Combined polyhedron and ball/s
Page 19 and 20: List of Tables 1.1 Selected M-M dis
Page 21 and 22: MO 6 octahedra surrounding a centra
Page 23 and 24: 1.1.1 The clathrate-like structure
Page 25 and 26: 7(MoO 4 ) 2− + 8H + → [Mo 7 O 2
Page 27 and 28: Fig. 1.4: Combined polyhedral/ball
Page 29 and 30: This planar structure was originall
Page 31: [X 2 M 18 O 62 ] 6− , the D 3h We
Page 35 and 36: Fig. 1.11: Monomeric (left) and dim
Page 37 and 38: Chapter 2 Experimental 2.0.1 Reagen
Page 39 and 40: 2.2 Preparation of starting materia
Page 41 and 42: as Cs 6 [P 2 W 5 O 23 ]·7H 2 O by
Page 43 and 44: was adjusted between 5-6 by additio
Page 45 and 46: Chapter 3 Results 3.1 The hybrid or
Page 47 and 48: Fig. 3.2: FTIR spectra of compound
Page 49 and 50: Fig. 3.3: W 183 NMR spectra of (CsN
Page 51 and 52: Fig. 3.5: Left: combined polyhedral
Page 53 and 54: formed upon crystallization and bot
Page 55 and 56: X-ray Crystallography A crystal of
Page 57 and 58: the presence of the four (CH 3 ) 2
Page 59 and 60: Fig. 3.10: Cyclic voltammogram of 2
Page 61 and 62: as a function of electrolyte compos
Page 63 and 64: was observed that could be traced t
Page 65 and 66: electrochemical set-up was an EG &
Page 67 and 68: Fig. 3.14: The central core of Sn(C
Page 69 and 70: of these fragments [88, 90]. For co
Page 71 and 72: diffractometer using Mo K α radiat
Page 73 and 74: Fig. 3.18: Side view of [{Sn(CH 3 )
Page 75 and 76: host−guest systems with large cav
Page 77 and 78: X-ray Crystallography Single crysta
Page 79 and 80: 3.5.2 Results and discussions Polya
Page 81 and 82: Fig. 3.26: Ball and stick represent
Page 83 and 84:
can distinguish between different m
Page 85 and 86:
Fig. 3.28: STM pictures of {Sn(CH 3
Page 87 and 88:
Fig. 3.31: Size distribution by int
Page 89 and 90:
3.6 The bis-phenyltin substituted,
Page 91 and 92:
Table 3.7: Crystal Data and Structu
Page 93 and 94:
tral belt in-between the two tin at
Page 95 and 96:
Fig. 3.35: 183 W NMR spectra of com
Page 97 and 98:
whereas they are five-coordinated (
Page 99 and 100:
investigated by scanning tunneling
Page 101 and 102:
3.8 The di-titanium substituted, lo
Page 103 and 104:
Fig. 3.37: Ball/stick (left), polyh
Page 105 and 106:
[As 2 W 19 O 67 (H 2 O)] 14− , [A
Page 107 and 108:
3.9 The cyclic trimeric-titanium su
Page 109 and 110:
Table 3.9: Crystal Data and Structu
Page 111 and 112:
Fig. 3.40: FTIR spectra of compound
Page 113 and 114:
Fig. 3.42: Side-view of compound 11
Page 115 and 116:
11 by 183 W-NMR (at 16.66 MHz on a
Page 117 and 118:
3.11 Structure and solution propert
Page 119 and 120:
472(w), 444(w) cm −1 . This proce
Page 121 and 122:
MHz in 10 mm tubes and the 111 Cd N
Page 123 and 124:
Fig. 3.47: 111 Cd NMR spectra of [C
Page 125 and 126:
in aqueous solution, so that the nu
Page 127 and 128:
of cadmium ions in 12 and 13 and it
Page 129 and 130:
doubtedly 183 W-NMR, but the parama
Page 131 and 132:
K): (relative intensities in parent
Page 133 and 134:
Fig. 3.49: Combined polyhedral/ball
Page 135 and 136:
Fig. 3.50: 183 W NMR spectrum of [I
Page 137 and 138:
(17) are isostructural. They consis
Page 139 and 140:
Fig. 3.53: 183 W NMR spectrum of [I
Page 141 and 142:
3.12.4 Conclusion We have synthesiz
Page 143 and 144:
[37] D. Gatteschi, O. Kahn, J. Mill
Page 145 and 146:
94:226403, 2005. [123] R. J. Hamers
Page 147 and 148:
[206] I. Loose, E. Droste, M. Bösi
Page 149 and 150:
NMR Spectra Fig. 3.54: 13 C NMR spe
Page 151 and 152:
Fig. 3.56: 31 P NMR spectrum of pol
Page 153 and 154:
Fig. 3.58: 13 C NMR spectrum of pol
Page 155 and 156:
Fig. 3.60: 1 H NMR spectrum of poly
Page 157 and 158:
Fig. 3.62: 119 Sn NMR spectrum of p
Page 159 and 160:
Fig. 3.66: 1 H NMR spectrum of poly
Page 161 and 162:
Fig. 3.70: 13 C NMR spectrum of pol
Page 163 and 164:
were applied and an absorption corr
Page 165 and 166:
Fig. 3.75: Size distribution by num
Page 167 and 168:
Table 3.16: Crystal Data and Struct
Page 169 and 170:
Fig. 3.80: FTIR spectra of compound
Page 171 and 172:
FIRASAT HUSSAIN International Unive
Page 173 and 174:
Publications 1. Observation of a Ha
Page 175 and 176:
PAPERS IN CONFERENCE/ SYMPOSIA / WO
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