Synthesis, structure, spectra and redox chemistry of iron(III) complexes of tridentate pyridyl and benzimidazolyl ligands

Abstract

A series of high-spin octahedral 1 : 2 iron(III) complexes of Schiff bases derived from salicylaldehyde and aromatic amines and the 1 : 1 and 1 : 2 complexes of bis(pyridin-2-yl)-aza and bis(benzimidazol-2-yl)-aza and -thioether ligands have been isolated. The crystal structure of trichloro[bis(pyridin-2-ylmethyl)amine]iron(III) has been determined. It contains two crystallographically independent molecules in the asymmetric unit cell. In each molecule iron(III) possesses a rhombically distorted octahedral co-ordination, constituted by all the three nitrogens of the facial ligand and three chloride ions. The effects of stereochemical and/or donor atom variations on the UV/VIS and EPR spectra and Fe^III–Fe^II redox potentials and hence on the Lewis acidity of the iron(III) centre are discussed. The phenolate-to-iron(III) charge-transfer band energy of [FeL¹₂]Cl [HL¹=N-(pyridin-2-ylmethyl)salicylideneamine] is higher and its Fe^III–Fe^II redox potential more negative than those of the corresponding 1 : 1 complex.