Author: ["Emily Y. Tsui","Rosalie Tran","Junko Yano","Theodor Agapie"]
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Abstract
Redox-inactive metals are found in biological and heterogeneous water oxidation catalysts, but, at present, their roles in catalysis are not well understood. Here, we report a series of high-oxidation-state tetranuclear-dioxido clusters comprising three manganese centres and a redox-inactive metal (M). Crystallographic studies show an unprecedented Mn3M(µ4-O)(µ2-O) core that remains intact on changing M or the manganese oxidation state. Electrochemical studies reveal that the reduction potentials span a window of 700 mV and are dependent on the Lewis acidity of the second metal. With the pKa of the redox-inactive metal–aqua complex as a measure of Lewis acidity, these compounds demonstrate a linear dependence between reduction potential and acidity with a slope of ∼100 mV per pKa unit. The Sr2+ and Ca2+ compounds show similar potentials, an observation that correlates with the behaviour of the oxygen-evolving complex of photosystem II, which is active only if one of these two metals is present. The presence of Ca2+ is essential for the activity of the oxygen-evolving complex (OEC) of Photosystem II, although its exact role is still unclear. Now, electrochemical measurements of structural mimics of the OEC — based on mixed-metal trimanganese dioxido complexes — reveal a correlation between the Lewis acidity of the redox-inactive metal and the reduction potential of the complex. Cite this article
Tsui, E., Tran, R., Yano, J. et al. Redox-inactive metals modulate the reduction potential in heterometallic manganese–oxido clusters. Nature Chem 5, 293–299 (2013). https://doi.org/10.1038/nchem.1578 