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

• Published in: Nature chemistry Vol. 2; no. 9; pp. 756 - 759
• Main Authors: Fukuzumi, Shunichi, Morimoto, Yuma, Kotani, Hiroaki, Naumov, Pance, Lee, Yong-Min, Nam, Wonwoo
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 01.09.2010
• Subjects: Alkanes - chemistry; Calcium - chemistry; Chemistry; Crystal structure; Electrons; Iron - chemistry; Models, Molecular; Oxidation-Reduction; Samarium - chemistry; Science; Japan
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/nchem.731

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.