Models for Heteropoly Blues. Degrees of Valence Trapping in Vanadium(IV)- and Molybdenum(V)-Substituted Keggin Anions.

摘要

Optical and esr spectra and polarographic redox potentials are reported for Keggin anions, all of which are intensely colored 'heteropoly blue'-like complexes. Single-crystal esr measurements prove that Mo(V) in PMoW11O404- occupies one of the twelve equivalent metal sites in the Keggin structure. The esr parameters for V(IV) in the tungstate and molybdate anions are significantly different and show the valence electron to be more firmly trapped on vanadium in the tungstates than in the molybdates. Analysis of the intervalence charge-transfer spectra of these complexes according to the method of Hush leads to a similar conclusion. Variations and trends of the reversible redox potentials of Keggin anions are discussed in terms of a 'localized' model for heteropoly blues and analogous complexes.