Synthetic cluster models of the biological oxygen evolving complex: Insights regarding function and spectroscopy

Abstract

Complex inorg. active sites perform challenging catalytic transformations in biol. systems, such as water oxidn. by Photosystem II and nitrogen redn. in Nitrogenase. The effect of cluster structure on the phys. and chem. properties of these active sites is not well understood. We have developed methodologies for the rational synthesis of tetra- and pentanuclear homo- and hetero-metallic cluster models of the Oxygen Evolving Complex in Photosystem II, which allow for systematic structure-property studies. Clusters displaying the cubane motif found in the OEC have been prepd., and the redox inactive metal was found to impact redox chem. Tetranuclear clusters that structurally model the dangler motif have also been synthesized, with open coordination sites for water coordination. Distal redox changes have been demonstrated to have a substantial effect on the reactivity of aquo, hydroxide, and oxo ligands relevant to water oxidn. Upon incorporation of second coordination sphere hydrogen bonding interactions, water oxidn. catalysis was obsd. Spectroscopic studies of models with structures or redox states relevant to the OEC provide benchmarking for the biol. system. Implications for the function and spectroscopy of the OEC will be discussed.

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