A BIS(MU-ALKOXO)DIIRON COMPLEX WITH NOVEL TERMINALLY LIGATED CARBOXYLATES

The diferric complex [Fe2(DBE)2(OBz)2](C104)2(DBE = 2-[bis(2-benzimidazolylmethyl)amino]ethanol) was synthesized and characterized by NMR, IR, magnetic susceptibility, and X-ray crystallography methods. The title complex crystallizes in the space group C2/c with Z = 4 (a = 14.889 (3), b = 18.055 (4), c = 24.728 (5) Å; β = 101.67 (2)°). The structure contains dimeric units where the two iron atoms are bridged by the oxygen atoms of the two DBE ligands, forming an Fe2(OR)2 core, and the two benzimidazoles on each tripod are coordinated trans to each other in planes perpendicular to the Fe202 core. The carboxylates are each ligated trans to one of the alkoxo bridges in an unusual coordination mode. The carbonyl oxygen is 2.89 (1) Å away from the iron center and appears to occupy a position in the coordination sphere. The iron(III) centers are antiferromagnetically coupled via the alkoxo bridges with J = −20.5 cm−1. Chemical reduction of the complex leads to the formation of a mixed-valence species, with EPR features at g = 1.94 and 1.79. The relevance of this complex to the active sites of the iron-oxo proteins is discussed. © 1990, American Chemical Society. All rights reserved.