Effects of Organic Solvents and Salts on the Isomerization Reaction (β→α) of Keggin-type 12-Molybdophosphate Anion

Abstract

The isomerization reaction of the β-form of 12-molybdophosphate ([PMo12O40](3-): PMo12) into the α-form in aqueous-organic mixed media containing various salts was extensively investigated with cyclic voltammetry. It was found that the concentration and type of organic solvent and salt strongly affected the rate of the isomerization reaction. When organic solvents with lower permittivity than water were used as auxiliary solvents, and high concentrations of salts were added to the reaction mixture, the β-form of PMo12 (β-PMo12) became more stable, leading to slow isomerization into the α-form (α-PMo12). Based on the results of this study, it is proposed that the isomerization reaction of β-PMo12 into α-PMo12 is caused by the attack of a proton on a corner-shared oxygen atom. Also, the variation of its reaction rate upon the addition of organic solvents and salts is due to interactions between both the protons and the solvents or anions, and between the cations and the PMo12 anion.