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

Nature Chemistry volume 5, pages 293–299 (2013)Cite this article

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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.

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Figure 1: Proposed structures of water oxidation catalysts containing redox-inactive metals (M) in the OEC (left, middle) and in heterogeneous cobalt oxide water oxidation catalysts (right)12,43.
Figure 2: Synthesis of tetrametallic trimanganese dioxido complexes.
Figure 3: Solid-state structures of reported complexes (thermal ellipsoids shown at 50% level).
Figure 4: The shift in the rising edge energy in the Mn XANES spectra.
Figure 5: The redox potentials of the [MMn3O2] complexes are correlated with the Lewis acidity of the redox-inactive metal.

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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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Authors and Affiliations

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

    Emily Y. Tsui & Theodor Agapie

  2. Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, 94720, California, 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.

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Correspondence to Theodor Agapie.

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Supplementary information

Supplementary information

Supplementary information (PDF 3845 kb)

Supplementary information

Crystallographic data for compound [1-Ca(DME)(OTf)](OTf)2 (CIF 42 kb)

Supplementary information

Crystallographic data for compound [1-Ca(H¬2O)3](OTf)3 (CIF 57 kb)

Supplementary information

Crystallographic data for compound [2-Ca(DME)(OTf)](OTf) (CIF 44 kb)

Supplementary information

Crystallographic data for compound [1-Sr(DME)(OTf)](OTf)2 (CIF 42 kb)

Supplementary information

Crystallographic data for compound [2-Sr(DME)(OTf)](OTf) (CIF 44 kb)

Supplementary information

Crystallographic data for compound [1-Zn(CH3CN)](OTf)3 (CIF 40 kb)

Supplementary information

Crystallographic data for compound [1-Na]2(OTf)4 (CIF 36 kb)

Supplementary information

Crystallographic data for compound [2-Y(DME)(OTf)](OTf)2 (CIF 63 kb)

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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

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