Medium Effects on the Redox Properties of 12-Molybdophosphate and 12-Molybdosilicate

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Abstract
The formal redox potentials of 12-molybdophosphate and 12-molybdosilicate up to the twelve-electron reduction per heteropolymolybdate ion were determined by cyclic voltammetry at a glassy carbon electrode in 50% (v/v) water-organic media containing some inorganic acids. These heteropolymolybdates in the presence of 1,4-dioxane (DO) or tetrahydrofuran (THF) display five two-electron reversible cathodic waves, followed by an irreversible two-electron wave, whereas the same heteropolymolybdates in the presence of 1,2-dimethoxyethane, N,N-dimethylformamide, acetonitrile, ethanol, or acetone yield five successive redox couples of 2,2,2,4, and 2e− (electrons) each. The eight-electron reduction species of 12-heteropolymolybdates are stabilized by cyclic ethers such as DO or THF. The stabilization of the eight-electron reduction species by the addition of a cyclic ether has been explained by taking into account the adduct formation between the molecules of the cyclic ether and 12-heteropolymolybdate.