Photocatalytic Water Oxidation by a Mixed-Valent MnIII3MnIVO3 Manganese Oxo Core that Mimics the Natural Oxygen-Evolving Center.

The functional core of oxygenic photosynthesis is in charge of catalytic water oxidation by a multi-redox Mn^III/Mn^IV manifold that evolves through five electronic states (S _i , where i=0-4). The synthetic model system of this catalytic cycle and of its S₀→S₄ intermediates is the expected turning point for artificial photosynthesis. The tetramanganese-substituted tungstosilicate [Mn^III₃Mn^IVO₃(CH₃COO)₃(A-α-SiW₉O₃₄)]⁶⁻ (Mn₄POM) offers an unprecedented mimicry of the natural system in its reduced S₀ state; it features a hybrid organic-inorganic coordination sphere and is anchored on a polyoxotungstate. Evidence for its photosynthetic properties when combined with [Ru(bpy)₃]²⁺ and S₂O₈²⁻ is obtained by nanosecond laser flash photolysis; its S₀→S₁ transition within milliseconds and multiple-hole-accumulating properties were studied. Photocatalytic oxygen evolution is achieved in a buffered medium (pH 5) with a quantum efficiency of 1.7 %. [ABSTRACT FROM AUTHOR]