Iron(II) and iron(III) low and high spin complexes formed from p-nitrophenolatoiron(III) complex of protoporphyrin-IX-dimethylester in the presence of 1-methylimidazole: magnetic circular dichroism and 1 H nuclear magnetic resonance spectroscopic studies

Abstract

Addition of imidazole (1-methylimidazole) to the p-nitrophenolatoiron(III) complex of protoporphyrin-IX-dimethylester showed very interesting features dependent on the nature of solvent and the ratio of the ligand to heme. The complexes formed under various conditions were iron(III) complexes with a phenolate anion and an imidazole, iron(III) complexes with two imidazoles, and a reduced (iron(II)) complex with two imidazoles. Absorption, magnetic circular dichroism, and 1H NMR spectroscopies were employed to identify the complexes. The reduced complexes were formed only in the presence of l-MeIm and in nonpolar solvents (toluene and benzene). This indicates that the oxidation-reduction potential of Fe(III) low-spin complex is higher than that of Fe(III) high-spin-complex and that the potential is higher in nonpolar solvent than that in polar solvent.