Crystal structure of a metal ion-bound oxoiron(IV) complex and implications for biological electron transfer
Shunichi Fukuzumi1, Yuma Morimoto, Hiroaki Kotani
1Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, SORST, Japan Science and Technology Agency, Suita, Osaka 565-0871, Japan. fukuzumi@chem.eng.osaka-u.ac.jp
Abstract:
Critical biological electron-transfer processes involving high-valent oxometal chemistry occur widely, for example in haem proteins [oxoiron(IV); Fe(IV)(O)] and in photosystem II. Photosystem II involves Ca(2+) 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 Ca(2+) and Sc(3+) to a non-haem oxoiron(IV) complex, [(TMC)Fe(IV)(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). As determined by X-ray diffraction analysis, an oxo-Sc(3+) 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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