Di-iron(III) complex of a hexadentate ligand with inequivalent iron coordination sites

Abstract

A binuclear iron(III) complex [ClFe(N 6)FeCl 3]Cl 2·3H 2O has been synthesized, where N 6 is the N-ethyl derivative of the hexadentate ligand N,N,N′,N′-tetrakis[(2-benzimidazolyl) methyl-1,2-ethanediamine. Variable temperature magnetic susceptibility in the temperature range of 80 < T < 300 K was least squares fitted, with J = −7.0 cm −1, supporting weak exchange coupling between the iron atoms. Mo¨ssbauer spectra for the di-iron complex at room temperature consist of two quadruple doublets of nearly equal area. The isomer shifts lie within the range for high spin ferric ions, while the small quadruple splittings are not consistent with the presence of an oxo bridge. Mo¨ssbauer data support the presence of distinct coordination environments for the two iron atoms. Such coordination environment asymmetry is also found for iron sites in purple acid phosphatase.