Photocatalytic Water Oxidation by a Mixed‐Valent Mn III 3 Mn IV O 3 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 S 0 →S 4 intermediates is the expected turning point for artificial photosynthesis. The tetramanganese‐substituted tungstosilicate [Mn III 3 Mn IV O 3 (CH 3 COO) 3 (A‐α‐SiW 9 O 34 )] 6− (Mn 4 POM) 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 S 2 O 8 2− is obtained by nanosecond laser flash photolysis; its S 0 →S 1 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 %.