Spin-Gated Selectivity of the Water Oxidation Reaction Mediated by Free Pentameric CaMnO Clusters.

We report on the first preparation of isolated ligand-free CaMnO gas-phase clusters, as well as other pentameric CaMnO ( = 0-4) clusters with varying Ca contents, which serve as molecular models of the natural CaMnO inorganic cluster in photosystem II. Ion trap reactivity studies with DO and HO reveal a pronounced cluster composition-dependent ability to mediate the oxidation of water to hydrogen peroxide. First-principles density functional theory simulations elucidate the mechanism of water oxidation, proceeding via formation of a terminal oxyl radical followed by oxyl/hydroxy (O/OH) coupling.