Manganese-calcium/strontium heterometallic compounds and their relevance for the oxygen-evolving center of photosystem II

• Review of the chemistry of heteronuclear manganese calcium/strontium as models of the oxygen-evolving-complex of photosystem II.
• Synthetic procedures for the heteronuclear complexes are highlighted.
• The relevance of the manganese calcium/strontium complexes with the structure of the oxygen-evolving-complex of photosystem II.

Manganese–calcium and manganese–strontium heteronuclear compounds are of considerable current interest in the context of modeling the structure of the oxygen-evolving complex (OEC) of photosystem II (PSII), an oxygen-bridged Mn4CaO5 cluster stabilized by carboxylate ligands. This review surveys the structures of all heteronuclear Mn–Ca and Mn–Sr complexes that have been synthesized and characterized by X-ray crystallography and establishes their relevance to the structure of the OEC. Polymers as well as discrete clusters from two up to fifteen metal ions were isolated in oxidation states ranging from +II to +IV, with various topologies and bridging ligands (µ-alkoxo, µ-hydroxo and µ-oxo). Although this area of research is relatively new, as most of the publications come from the last five years, impressive advances have been recently achieved with the isolation of two close synthetic structural mimics of the cubane subunit Mn3CaO4 of the OEC in 2011 and one mimic of the whole cluster in 2015.

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