A biologically relevant iron(III) phenoxyl radical complex: A thermodynamic investigation on the structure-radical stability relationship

A kind of new amine-chloro substituted phenol and its iron(III) complex has been prepared and characterized by spectroscopic, X-ray techniques and magnetic susceptibility studies. X-ray analysis revealed a binuclear complex, Fe2(LTHF)3 in which two Fe(III) centers were surrounded by three ligands. The magnetic susceptibility indicates antiferromagnetic coupling between two iron centers through phenolate bridges. Voltammetric study of ligand (H2LTHF) and complex Fe2(LTHF)3 revealed that the coordinated phenolate ligands undergo reversible two-electron oxidations with formation of coordinated phenoxyl radicals. It has seen that the oxidation of Fe2(LTHF)3 comparing to its analog, Fe2(LtBu)2 occurs at significantly higher potentials. It was attributed to the relationship between the radical stability with electronic and steric properties of ligands. Stability constants and thermodynamic parameters for the formation of Fe2(LTHF)3 complex and the role of ligand coordination to iron center in phenoxyl radical stabilization has been investigated using anodic peaks potentials.