Manganese-phosphomolybdate molecular catalysts for the electron transfer reaction of ferricyanide to ferrocyanide

Abstract

Three manganese-containing phosphomolybdate hybrids (H₂bpp)₅[Na(Hbpp)]₆H₁₀{Mn[Mo₆O₁₂(OH)₃(HPO₄)₄]₂}₄·14H₂O (1), [Na₄(H₂bpp)₂Mn(H₂O)₇]{Mn[Mo₆O₁₂(OH)₃(HPO₄)₃(PO₄)]₂}·2H₂O (2), and Na(H₂O)₂(Hbpp)₃[Na₂(bpp)(H₂O)][Mn₂(H₂O)₅]{Mn[Mo₁₂O₂₄(OH)₆(HPO₄)₆(H₂PO₄)(PO₄)]}·(HPO₄)·H₂O (3) (bpp = 1,3-bi(4-pyridyl)-propane) have been constructed and characterized. The inorganic moieties of the three hybrids consist of ‘hourglass-shaped’ anionic clusters, composed of two reduced polymolybdenum phosphate units [P₄^VMo₆^VO₂₈(OH)₃]₉ {P₄Mo₆} bridged by one manganese ion. Preliminary experiments show that these hybrids, as a unique class of molecular catalyst, are highly active for promoting the inorganic electron transfer (redox) reaction of ferricyanide to ferrocyanide by thiosulphate with high rate constants under mild conditions. These catalysts maintain their structural identity both in solution and solid state and can be easily separated from the reaction solution for the next catalytic cycle.