Redox properties of hybrid Dawson type polyoxometalates disubstituted with organo-silyl or organo-phosphoryl moieties

This paper reports on the electrochemical study of Dawson-type polyoxometalates (POMs) disubstituted with phenyl-phosphonate, phenyl silyl or tertbutylsilyl moieties. The polyanions were studied by cyclic voltammetry and on rotating disk electrode in acetonitrile with tetraphenylphosphonium chloride as supporting electrolyte. We found that these hybrid polyoxometalates can accept up to five electrons and that the organic substituents modify the first and second reduction potential of the POM compared to the unsubstituted POM [P2W18O62](6-). Phenyl-phosphonate lowers the reduction potential, whereas the phenyl silyl or tertbutylsilyl moieties shift them cathodically. We also recorded by spectroelectrochemistry the spectrum of the monoreduced and the bisreduced species of the polyoxometalate disubstituted with phenyl-phosphonate. (c) 2007 Elsevier Ltd. All rights reserved.