A new Fe-III (mu-OCH3)(2)(mu-OAc)Fe-III complex containing phenolate and imidazole ligands as a structural model for the active site of non-heme diiron enzymes

摘要

A new tridentate ligand [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine (HBHA) and its first dinuclear Fe-III complex have been synthesized. The crystal structures of HBHA and of the complex [Fe-2(III)(BHA)(2)(mu -OCH3)(2)(mu -OAc)]- (ClO4) (1) have been solved by X-ray crystallography. In the cation of complex 1, each BHA(-) anion is arranged in a facial mode while one acetate and two methoxo groups as bridging ligands complete the coordination spheres of the Fe-III centres. The Fe-III ions are weakly antiferromagnetically coupled (J = -10.1 cm(-1)) and undergo a quasi-reversible one-electron redox process attributed to the Fe-2(III)/(FeFeIII)-Fe-II couple. Complex 1 also displays an intense phenolate-to-Fe-III charge transfer transition at 517 nm (epsilon = 5560 dm(3) mol(-1) cm(-1)/Fe-2(III)). The Mossbauer spectrum of 1 at 115 K shows only one quadrupole doublet, with delta = 0.47 and DeltaE(Q) = 0.80 mm s(-1). A comparison of the structural, magnetic and spectroscopic properties of 1 and those detected in the Fe-2(III) form of purple acid phosphatases suggests that this compound is a potential structural model for the active site of these metalloenzymes. In addition, complex 1 also mimics some structural features found in methane monooxygenase. [References: 60]