Mössbauer effect study of tight spin coupling in oxidized chloro-5,10,15,20-tetra(mesityl)porphyrinatoiron(III)

Abstract

Mossbauer spectra of a polycrystalline form of oxidized chloro-S, 10, 15,20-tetra(mesityl)porphyrinatoiron(lIl) [Fe(TMP)Cl], compound A, were recorded over a range of temperatures (4,2-195 K) and magnetic fields (0-6 T), These spectra of compound A exhibit magnetic features which are markedly different from those of the analogous protein complexes, horse radish peroxidase compound I (HRP-I) and compound ES of cytochrome c peroxidase, even though chemical evidence and optical spectroscopy indicate that compound A is similar to the others in comprising a Fe(IY) complex within a porphyrin cation radicaL We interpret the data by employing a spin Hamiltonian model in which the central Fe(IY) complex, with S = 1, is tightly coupled to a S = 1/2 system of the oxidized porphyrin to yield a net S = 3/2 system as suggested by the susceptibility measurements. The theoretical treatment yields information on the d -electron energies which is similar to that more directly available in the peroxidase spectra. The strength of the axial crystal field is found to increase progressively in the series HRP-I, ES, compound A, while the spin coupling in A is the strongest of the three by several orders of magnitude. The good fits to experimental data confirm the efficacy of the theoretical treatment which may be applicable to a variety of other coupled systems.

Iron corrolates: Unambiguous chloroiron(III) (corrolate)2− π-cation radicals

“…[20] with permission from the American Chemical Society. chloroiron complex is in the range usually expected for Fe(III) [56][57][58][59], while that of the phenyliron complex is in the range usually expected for Fe(IV) [60,61] (however, see next-to-last paragraph of Section 6). The magnetic Mö ssbauer spectra of the chloroiron-and the phenyliron(7,13-dimethyl-hexaethylcorrolate) complexes are shown in Figs.…”

Transition Metal Complexes and the Activation of Dioxygen

“…Compound 23a (Figure 9) is the earliest and most studied examples of a Cpd I model, which was shown by Mössbauer and EPR studies to be an S ¼ 3/2 system, in which a triplet Fe(IV) center is ferromagnetically coupled (J ¼ 43 cm to an a 2u porphyrin radical [63,64]. Electron-withdrawing aryl rings (23b-e) have been shown to weaken ferromagnetic interaction and even result in a change in symmetry of the porphyrin radical (23e) from a 2u to a 1u as confirmed by 1 H NMR and EPR studies [65,66].…”

High-valent iron in chemical and biological oxidations

“…Another type of iron(IV) porphyrin isolated at that time was a dimethoxy derivative [65]. These compounds have been extensively studied and well characterized by various spectroscopic techniques, including visible spectroscopy, NMR, EPR (electron paramagnetic resonance), Mö ssbauer and EXAFS [65][66][67][68][69][70][71][72][73].…”