Reactivity of Bis(μ-hydroxo) Divanadium Site in γ-H₂SiV₂W₁₀O₄₀^4- with Hydroxo Compounds

The reactivity of divanadium-substituted silicotungstate, γ-H2SiV2W10O404- (I), with hydroxo compounds of alcohols, carboxylic acids, and water is reported. The reaction of the bis(μ-hydroxo) divanadium site in I with primary alcohols and formic acid smoothly proceeds to form corresponding monoesters and monoformate, respectively, and the crystal structures of the monomethyl and monoethyl esters and the monoformate of I are determined. The oxygen exchange between the hydroxo group and water proceeds easily. On the other hand, bulky compounds of 2-propanol, tert-butyl alcohol, and acetic acid hardly react with the bis(μ-hydroxo) divanadium site (equilibrium constant < 0.01) because of the steric crowding between the methyl groups and the polyoxometalate framework.