Dodecatungstosilicic Acids Isomers and Related Lacunary Compounds

and y-DODECATUNGSTOSILICIC ACIDS ISOMERS AND RELATED LACUNARY COMPOUNDS 

The dodecatungstosilicates are stable in acid solution. When the pH increases, hydrolytic cleavages of W—O bonds occur, leading to well-defined lacunary polyanions, with 11, 10, or 9 tungsten atoms. 

The most stable compounds, or least labile when they are metastable, are obtained with Si as the heteroelement. Three dodecatungstosilicates, four undecatungstosilicates, one decatungstosilicate, and two nonatungstosi-licates are known. They are prepared following the general route in Fig. 1. 

The lacunary polyanions can act as ligands with numerous metal cations, leading to mono-, di-, or trinuclear complexes according to the number of vacant sites. These complexes are the earliest model materials of mixed oxides, and they are important for catalytic purposes, particularly for the oxidation of organic substrates. 

These polyanions differ only slightly in their compositions hence, elemental analysis is not a reliable criterion of purity. It is more convenient to characterize the heteropolyanions by their physicochemical properties UV-Vis spectrum and polarogram in solution and IR spectrum in the solid 

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A. Teze, G. Herve, rz-, p-, and y-Dodecatungstosilicic acids Isomers and related lacunary compounds, Inorg. Synth. T7 (1990) 85. 

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