Photocatalytic Water Oxidation by a Mixed-Valent Mn3IIIMnIVO3 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 S0S4 intermediates is the expected turning point for artificial photosynthesis. The tetramanganese-substituted tungstosilicate [(Mn3MnO3)-Mn-III-O-IV(CH3COO)(3)(A--SiW9O34)](6-) (Mn4POM) offers an unprecedented mimicry of the natural system in its reduced S(0)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 S0S1 transition within milliseconds and multiple-hole-accumulating properties were studied. Photocatalytic oxygen evolution is achieved in a buffered medium (pH5) with a quantum efficiency of 1.7%.