Visible-Light Water Oxidation by a Polyoxometalate Complexed 275 Iron-Atom Hematite Core.

Although metal-oxide nanocrystals are often highly active, rapid aggregation (particularly in water) generally precludes detailed solution-state investigation of their catalytic reactions. This is equally true for visible-light driven water oxidation by hematite α-Fe2O3 nanocrystals, that bridge a conceptual divide between molecular complexes of iron and solid-state hematite photoanodes. We now report that the aqueous solubility and remarkable stability of polyoxometalate- (POM-) complexed 275 iron-atom hematite cores make it possible to investigate visible-light driven water oxidation at this frontier area, by application of the versatile toolbox of solution-state methods typically reserved for molecular catalysis. These reveal a unique mechanism, understood as a general consequence of fundamental differences between reactions of solid-state metal oxides and freely diffusing "fragments" of the same material.