Magnetic and Spectroscopic Characterization of an Iron Porphyrin Peroxide Complex. Peroxoferrioctaethylporphyrin(1-)

Article abstract of DOI:10.1021/ja00213a009

A ferric porphyrin peroxide complex, which is possibly analogous to an oxygenated intermediate involved in reactions of cytochrome P450, has been isolated and characterized.The tetramethylammonium salt of peroxoferrioctaethylporphyrin, , was prepared by the reaction of Fe^III(OEP)Cl with 2 equiv of tetramethylammonium superoxide in acetonitrile and isolated by cooling to -30 deg C.An elemental analysis of the microcrystalline solid was consistent with the formulation above.Magnetic susceptibility measurements on the solid material gave a value of 5.75μ_B for the effective magnetic moment, confirming the high-spin ferric state of the iron atom in this complex.Moessbauer spectra, which exhibited an isomer shift of +0.67 mm/s, and ESR spectra, with g values of 4.2 and 9.5, were also consistent with a high-spin ferric iron.The data from the Moessbauer, magnetic susceptibility, and powder ESR measurements were succesfully simulated by a rhombic spin Hamiltonian.The magnitude of D was determined to be approximately 0.85 cm^-1 with λ = E/D = 0.29, close to the rhombic limit of 0.33.On the basis of these data, the energy difference between the two lowest Kramers' doublets is approximated at 2.9 cm^-1.