Abstract
Critical biological electron-transfer processes involving high-valent oxometal chemistry occur widely, for example in haem proteins [oxoiron(IV); FeIV(O)] and in photosystem II. Photosystem II involves Ca2+ as well as high-valent oxomanganese cluster species. However, there is no example of an interaction between metal ions and oxoiron(IV) complexes. Here, we report new findings concerning the binding of the redox-inactive metal ions Ca2+ and Sc3+ to a non-haem oxoiron(IV) complex, [(TMC)FeIV(O)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). As determined by X-ray diffraction analysis, an oxo-Sc3+ interaction leads to a structural distortion of the oxoiron(IV) moiety. More importantly, this interaction facilitates a two-electron reduction by ferrocene, whereas only a one-electron reduction process occurs without the metal ions. This control of redox behaviour provides valuable mechanistic insights into oxometal redox chemistry, and suggests a possible key role that an auxiliary Lewis acid metal ion could play in nature, as in photosystem II.
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Acknowledgements
This work was supported by a Grant-in-Aid (no. 20108010 to S.F.) and a Global COE program, ‘the Global Education and Research Center for Bio-Environmental Chemistry’ from the Ministry of Education, Culture, Sports, Science and Technology, Japan (to S.F.), and NRF/MEST through a WCU project (R31-2008-000-10010-0) (to S.F. and W.N.) and the Creative Research Initiatives Program (to W.N.). Crystallographic data for [(TMC)FeIV(O)–Sc(OTf)4(OH)] have been deposited with the Cambridge Crystallographic Data Center under reference numbers CCDC-742067 (X-ray).
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S.F., Y.M., H.K. and W.N. conceived and designed the experiments. Y.M. and P.N. performed the experiments. Y.M., H.K. and P.N. analysed the data. P.N. and Y.M.L. contributed materials and analysis tools. S.F. and W.N. co-wrote the paper.
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Fukuzumi, S., Morimoto, Y., Kotani, H. et al. Crystal structure of a metal ion-bound oxoiron(IV) complex and implications for biological electron transfer. Nature Chem 2, 756–759 (2010). https://doi.org/10.1038/nchem.731
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DOI: https://doi.org/10.1038/nchem.731
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