School of Engineering and Science - Jacobs University

More documents

Recommendations

Info

β,γ,δ and ɛ are derived from the α-isomer, a cluster already mentioned above, by rotation of 60 ◦ of 1, 2, 3, and 4 different triads respectively. which can form [XM 11 O 39 ] n− and Fig. 1.9: Schematic representation of the formation of Keggin-type lacunary. Courtesy: Dr. Santiago C. Reinoso [XM 9 O 34 ] n− species by the ‘removal’ of one or three adjacent MO 6 octahedra respectively. An intermediate structure in which two adjacent octahedra have been removed has not been observed for the α and β isomers but observed only for the γ isomer; in the former two cases the structure would contain an MO 6 octahedron with three fac terminal oxygen atoms and is therefore expected to be quite reactive. Two kinds of the XM 9 anions can be formed, both having C 3v symmetry: A-type, in which three corner-shared octahedra have been lost, and B-type, in which three edge-shared octahedra have been lost. Neither of these sructures appears to be thermodynamically stable in solution, although both have been isolated as solids salts, and used to synthesize derivatives. In addition, both A- and B-type XM 9 structural units are recognizable in larger polyoxoanions. Examples are: 11
[X 2 M 18 O 62 ] 6− , the D 3h Wells-Dawson structure formed by fusion of two A-XM 9 units; [As 2 W 21 O 69 ] 6− and [P 2 W 21 O 71 ] 6− , which contain two B- and A-type XW 9 units respectively separated by a ‘belt’ of three WO 6 octahedra; and [(NH 4 )As 4 W 40 O 140 ] 27− , containing four B-type AsW 9 units. The large tungstoarsenate(III) [As 6 W 65 O 217 (H 2 O) 7 ] 26− is the only example of a polyanion that contains both (α-AsW 9 O 33 ) and (β-AsW 9 O 33 ) isomers in the same structure [33]. Many of these larger structures can be further converted to lacunary species, e.g. X 2 M 18 (X= P, As) (‘Wells-Dawson structure’) yields X 2 M 17 , X 2 M 15 , and X 2 W 12 anions. Salts of the anions [AsW 9 O 33 ] 9− and [SbW 9 O 33 ] 9− were first reported by Rosenheim, and structurally confirmed by Krebs [34] and Tourné [35]. The anions appear to be stable at pH 7.5 to 9.0 and the potassium salts crystallize in a face centered cubic form isotypic with several lacunary Keggin salts mentioned earlier. This suggests an incomplete Keggin structure probably of B-type statistically oriented in the cubic cell. In contrast to the A-type 1:9 anions (Si, Ge, etc.), As III W 9 and Sb III W 9 do not react with tungstate to give As III W 11 and Sb III W 11 . However, solutions of the anions react with electrophiles to give complexes. These lacunary species derived from the Keggin type structure, are obtained from the three Baker-Figgis (α, β, γ) isomers by means of the elimination of a variable number of octahedra, so that a total of nine species are known whose structures are shown in above Figure 1.9 In the case of phospho-tungstate system, the reaction patterns are similar to those of the silico-tungstates, but a series of remarkable differences exists, which can be visualized from the Figure 1.10 The β-isomers are much more unstable and isomerize to the α-isomers, with the exception of the trivacant species A- β-[PW 9 O 34 ] 9− , which forms on acidifying solutions of tungstate and phosphate to pH around 9. When the reaction is carried out at 0 ◦ C, the A-α-isomer is obtained but it isomerizes to the A-β-isomer at room temperature. In addition, the dilacunary species γ-[PW 10 O 36 ] 7− is not synthesized directly, but by overnight refluxing of polyanion [P 2 W 5 O 23 ] 6− , overnight at pH = 7 and it is only isolated with 12
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: This planar structure was originall
Page 33 and 34: [P 2 W 19 O 68 (HO)] 14− , [P 2 W
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
show all

School of Engineering and Science - Jacobs University

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?