Synthesis and characterization of mononuclear octahedral Fe(III) complex containing a biomimetic tripodal ligand, N-(benzimidazol-2-ylmethyl) iminodiacetic acid

Abstract

The mononuclear iron complex 1, FeIII(Hbida)Cl(H2O), was synthesized using a tripodal tetradentate ligand, N-(benzimidazol-2- ylmethyl)iminodiacetic acid (H3bida), which has two carboxylate groups, one benzimidazoyl group, and one tertiary amine where it serves as a tetradentate chelating ligand for the octahedral Fe(III) ion. The four equatorial positions of the octahedral complex are occupied by two monodentate carboxylates, a benzimidazole nitrogen, and an oxygen of a water molecule. One of the axial positions is occupied by an apical nitrogen of the Hbida and the other by a chloride anion. The mononuclear octahedral complex 1 mimics the geometry of the key intermediate structure of the catalytic reaction cycle proposed for the FeSODs, which is a distorted octahedral geometry with three histidyl imidazoles, an aspartyl carboxylate, a superoxide anion, and a water molecule. The redox potential of complex 1, E1/2 is -0.11V vs. Ag/AgCl (0.12 V vs. NHE), which is slightly lower than those reported for the most FeSODs. The magnetic susceptibility of complex 1 at room temperature is 5.83 μB which is close to that of the spin only value, 5.92 μB of high-spin d5 Fe(III).