Spin-coupling in ferric metalloporphyrin radical cation complexes: Mössbauer and susceptibility studies

Abstract

Articles you may be interested inStudy of the electronic states of the allyl radical using spin-coupled valence bond theory Susceptibility and Mössbauer study of coupled admixedspin state in [Fe(OEP) (3ClPy)]+ dimers J. Chem. Phys. 85, 5212 (1986); 10.1063/1.451686 Mössbauer and susceptibility study of interheme spin coupling in [Fe (OEP) (2MeHIm)]+ dimers J. Chem. Phys. 83, 5945 (1985); 10.1063/1.449626Mössbauer studies of lowsymmetry crystal fields in lowspin ferric heme complexesThe ferric metalloporphyrin1T-radical cation complexes Fe (III) (OCI0 3 lz (TPP') and [Fe(1I1) CI (TP~')] [SbC1 6 ] were examined in microcrystalline form by MOssbauer spectroscopy and magnetIc susceptometry over a range of temperatures and applied fields. All measurements on the six-coordinate Fe(OCI0 3 lz (TPP' ) were consistent with isolated molecules having an S = 5/2 iron site with zero field splitting (12 cm -I) S: that is ferromagnetically coupled to the S = 1/2 porphyrin radical by an energy term ( -110 cm -I) SOS. Thus the ground state is overall spin-3.In the five-coordinate [FeCI (TPP' )] [SbC~] the susceptibility is in reasonable agreement with the results of a calculation based on zero field splitting (12 cm -I) S: for the S = 5/2 iron and antiferromagnetic coupling (200 cm -I) SOS with the radical to give an overall spin-2 ground state.However, the MOssbauer measurements require a more complicated model having the same large intramolecular iron-radical coupling, a smaller zero field splitting (3 cm -I) S:, and weak intermolecular antiferromagnetic coupling between heme pairs given by (32 cm -I) S os or . al 1 1 1 2 , eqwv ent y, (0.65 cm-) SI"S2' A slightly improved correspondence with the measured susceptibility results. The intermolecular antiferromagnetic coupling probably results from crystallization of the [FeCI (TPP' )] + cations in face-to-face dimers as observed in other closely related five-coordinate iron (III) porphyrins.

Chemistry of iron oxophlorins. 2. Oxidation of the iron(III) octaethyloxophlorin dimer and observation of stepwise, two-electron oxidation of the oxophlorin macrocycle

“…NMR data for BrFeIH(OEPO") and related complexes are given in Table I. Figure 2 shows the NMR spectrum of the complex in chloroform-d at 24 °C. Individual resonances are readily identified on the basis of their intensity and the fact that, in general, the meso protons, which are closer to the iron than the methylene or methyl protons, give the broadest resonances.…”

Temperature dependence and electronic transition energies in the magnetic circular dichroism spectrum of horeseradish peroxidase compound I

“…Figure 2 shows the combined effect of reducing the temperature from 92 to 3.5 K and varying the magnetic field from 4. 56 Effect of temperture on the MCD spectrum of HRP compound I. The temperatures range between 3.5 and 92 K. The spectra, which are normalized to 1 T and lie within the linear limit of the saturation curve, were recorded with magnetic fields between 1.27 and 4.56 T. For presentation purposes, the spectra in this plot were smoothed by using a FFT digital filter.…”

[Fe(OEP•)(X)]+ π-Cation Radicals: Characterization and Spin−Spin Interactions

“…We have been able to produce acceptable fits to the data for the bromide and chloride complexes with two models that treat the coupling between the spins somewhat differently. The first model is that which we described previously 14 for [Fe(OEP • )(Cl)] 2 [SbCl 6 ] 2 and which had been developed by Lang et al for [Fe(TPP • )(Cl)][SbCl 6 ]. In this model, there are three terms in the total Hamiltonian: an axial zero-field splitting parameter D for the high-spin iron, an intramolecular magnetic coupling −2 J Fe - r ( S⃗ · s⃗ ) between the iron spin S = 5 / 2 and the π-cation radical s = 1 / 2 spin, and an intermolecular coupling −2 J R - R ( S⃗ + s⃗ )·( S⃗ ‘ + s⃗ ‘) between the total spins on each half of the dimer.…”