Keggin structures heteropolyanions

Isopolyanions and Heteropolyanions Table 6 Keggin Structure Heteropolyanions... 

Several deficit or lacunary derivatives of the Keggin structure exist as individual species or as fragments of other heteropolyanion structures. Removal of one M06 octahedron (stoichiometric loss of MO"+) from a- or /3-Keggin anions leads to isomers of [XM11O39]"-. Removal of three adjacent octahedra leads to A- and B-type XM9034 anions. The structures of these are shown in Figure 11. 

Mo-heteropolyanions with a Keggin structure are readily reduced to give heteropoly blue in solution. A trend exists toward anions with X of higher charge (small value of n) being more easily reduced, while the reduction potential decreases in the order V > Mo > W. In the case of XMnWn04oH2", the Mn + in the anion is oxidized by O2. 

The stereochemical requirements of the heteroatoms generally determine the architecture of the heteropolyanions formed. This is illustrated by the Keggin structure (Figure 7)... 

Niu, J., Zhao, J. Wang, J. et al. (2004) Synthesis, property and crystal structure of a novel two-dimensional network organic-inorganic hybrid compound based on the neodymium center and Keggin-type heteropolyanion of [a- N Journal of Molecular Structure, 699, 85-92. 

Catalysts. Co(N03)2-6H20 was of pure grade. CoNaY zeolite and tetra-n-butylammonium salts of PWiiCo and CoW 12 heteropolyanions were obtained as described in [19] and [25], respectively. The content of cobalt in the CoNaY zeolite was 3.29 % wt. The formation of the Keggin structure and the purity of C0W12 and PWuCo were confirmed by 0 and P NMR, respectively. 

Metal oxygen cluster compounds with keggin structure have received attention as acid catalysts for several acid catalysed reactions in the liquid as well as in vapour phase conditions [1-6]. Studies on a series of salts with monovalent cations and various heteropolyanions have revealed that certain of these solids in particular those containing potassium, cesium,ammonium and thallium cations possess microporous structure [7-11]. Photoacoustic FTIR investigations and the studies on the chemisorption of ammonia and pyridine have shown that residual protons remain and these protons are responsible for the catalytic activity[12,13]. 

Kala-Azar, 278 Keggin anions, 1034 electrochemistry, 1050 Keggin structures, 1035 heteropolyanions, 1037 Klebsiella pneumoniae nitrogenases, 1425 Kroll process, 325 Krypton compounds difluorides, 313 fluoride, 313... 

As it hcis been found by detailed studies the preparation procedures described in the previous section allow to obtain conjugated polymers doped by heteropolyanions of Keggin structure. 

It has been shown that conjugated polymers, such as polyacetylene, polypyrrole and polyaniline can be doped with heteropolyanions of Keggin structure. They constitute a new type of catalytic support at which catalytically active species are dispersed on the molecular scale. 

Two major subsets of polyoxometalates are the isopolyoxometalates (or isopolyanions) which contain only transition metal and oxide ions, and the heteropolyoxometalates (or heteropolyanions) which contain one or more "heteroatoms" in addition to the transition metal and oxide ions. The heteroatom in polyoxometalates can be one of many elements in the p or d blocks. In this review we have highlighted the photochemistry of two polyoxometalates, dodecatungstophosphate, a representative heteropolyanion of the common Keggin structure, and decatungstate, a representative isopolyanion, whose structures are given in Figure 1. 

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