SYNTHESIS, STRUCTURE, SPECTRA AND REDOX CHEMISTRY OF IRON(III) COMPLEXES OF TRIDENTATE PYRIDYL AND BENZIMIDAZOLYL LIGANDS

A series of high-spin octahedral 1:2 iron(III) complexes of Schiff bas es 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 an d -thioether ligands have been isolated. The crystal structure of tric hloro[bis(pyridin-2-ylmethyl)amine]iron(III) has been determined. It c ontains two crystallographically independent molecules in the asymmetr ic unit cell. In each molecule iron(III) possesses a rhombically disto rted octahedral co-ordination, constituted by all the three nitrogens of the facial ligand and three chloride ions. The effects of stereoche mical and/or donor atom variations on the UV/VIS and EPR spectra and F e-III-Fe-II redox potentials and hence on the Lewis acidity of the iro n(III) centre are discussed. The phenolate-to-iron(III) charge-transfe r band energy of [FeL(2)(1)]Cl[HL(1) = N-(pyridin-2-ylmethyl)salicylid eneamine] is higher and its Fe-III-Fe-II redox potential more negative than those of the corresponding 1:1 complex.