Reactivity of bis(μ-hydroxo) divanadium site in γ-H ₂SiV₂W₁₀O₄₀^4- with hydroxo compounds

The reactivity of divanadium-substituted silicotungstate, γ-H ₂SiV₂W₁₀O₄₀^4- (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.