Crystal structure of a metal ion-bound oxoiron(IV) complex and implications for biological electron

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. The interactions of metal ions with metaloxo species are crucial in many important biological processes, such as the oxygen-evolving complex (OEC) in photosystem II, but their exact function remains elusive. Now, the binding of metal ions to a non-haem oxoiron complex has been studied and the observed changes to its electron-transfer properties provide insights into the active site of the OEC.

Cite this article

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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