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Redox-inactive metals modulate the reduction potential in heterometallic manganese–oxido clusters

Nature Chemistry volume 5, pages 293299 (2013) | Download Citation

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.

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Acknowledgements

This work was supported by the California Institute of Technology, the Searle Scholars Program, an NSF CAREER award (CHE-1151918 to T.A.) and the NSF Graduate Research Fellowship Program (to E.Y.T.). The authors thank L.M. Henling and D.E. Herbert for assistance with crystallography, and P-H. Lin for assistance with magnetic susceptibility studies. The Bruker KAPPA APEXII X-ray diffractometer was purchased with an NSF Chemistry Research Instrumentation award to Caltech (CHE-0639094). The X-ray spectroscopy work was supported by the NIH (grant no. F32GM100595 to R.T.) and by the Director of the Office of Basic Energy Science (OBES), Division of Chemical Sciences, Geosciences, and Biosciences, DOE (contract no. DE-AC02-05CH11231 to J.Y.). Synchrotron facilities were provided by the Stanford Synchrotron Radiation Lightsource (SSRL), operated by the DOE, OBER.

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Affiliations

  1. Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard MC 127-72, Pasadena, California 91125, USA

    • Emily Y. Tsui
    •  & Theodor Agapie
  2. Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Rosalie Tran
    •  & Junko Yano

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Contributions

E.Y.T. and T.A. designed the research. E.Y.T. and R.T. performed the experiments. R.T. and J.Y. provided XANES characterization. E.Y.T., R.T., J.Y. and T.A. analysed data. E.Y.T. and T.A. wrote the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Theodor Agapie.

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Crystallographic information files

  1. 1.

    Supplementary information

    Crystallographic data for compound [1-Ca(DME)(OTf)](OTf)2

  2. 2.

    Supplementary information

    Crystallographic data for compound [1-Ca(H¬2O)3](OTf)3

  3. 3.

    Supplementary information

    Crystallographic data for compound [2-Ca(DME)(OTf)](OTf)

  4. 4.

    Supplementary information

    Crystallographic data for compound [1-Sr(DME)(OTf)](OTf)2

  5. 5.

    Supplementary information

    Crystallographic data for compound [2-Sr(DME)(OTf)](OTf)

  6. 6.

    Supplementary information

    Crystallographic data for compound [1-Zn(CH3CN)](OTf)3

  7. 7.

    Supplementary information

    Crystallographic data for compound [1-Na]2(OTf)4

  8. 8.

    Supplementary information

    Crystallographic data for compound [2-Y(DME)(OTf)](OTf)2

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https://doi.org/10.1038/nchem.1578

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