Redox-inactive Metals Modulate the Reduction Potential in Heterometallic Manganese-Oxido Clusters

Nat Chem. 2013 Apr;5(4):293-9. doi: 10.1038/nchem.1578. Epub 2013 Mar 3.

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 Sr(2+) and Ca(2+) 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Calcium / chemistry
  • Catalysis
  • Crystallography, X-Ray
  • Electrochemistry
  • Manganese Compounds / chemistry*
  • Molecular Structure
  • Organometallic Compounds / chemical synthesis*
  • Organometallic Compounds / chemistry*
  • Oxidation-Reduction
  • Oxygen / chemistry*
  • Strontium / chemistry
  • Water / chemistry*
  • Zinc / chemistry

Substances

  • Manganese Compounds
  • Organometallic Compounds
  • Water
  • Zinc
  • Oxygen
  • Calcium
  • Strontium