SUBSTITUTION AND STABILITY EFFECTS IN HETEROPOLYACIDS - A THEORETICAL-ANALYSIS OF THE DIVERSITY OF THE KEGGIN ION

In this work, the redox effects and stability of a series of analogous [X((n))Mo12O40]((8-n)-) and [X((n))W12O40]((8-n)-) heteropolyanions a re assessed. Both of these homologs display the alpha-Keggin structure in which a tetrahedral oxyanion helps to satisfy the coordination sph ere of the metal oxide octahedron of the clathratic shell. Here, resul ts from a series of semiempirical electronic-structure calculations ar e used to illustrate the electronic effects induced by chemical modifi cations. The stability trends produced in this work reliably trace the experimental trends and present the description of electronic feature s required for stabilization of the Keggin ion. In addition, understan ding these electronic effects induced by chemical modification is crit ical in the rational design of heteropolymetallate catalysts. (C) 1995 Academic Press,Inc.