Pulsed EPR Characterization of the Low-Spin Iron(III) Porphyrinate Complexes with Phenyl Isocyanide Ligands Having the dxy Orbital Ground State

Abstract

Pulsed electron−nuclear double resonance and electron spin−echo envelope modulation spectroscopies have been used to characterize the bis(phenyl isocyanide) complexes of iron(III)-tetraphenylporphyrin ([TPPFe(PhNC)2]+) and iron(III)-octaethylporphyrin ([OEPFe(PhNC)2]+) that have the dxy orbital configuration. The spin density distribution in the porphyrin π system was obtained, with major spin density (∼0.06) being delocalized to each meso carbon atom. The spin density on the pyrrole β carbons was found to be negligible. The upper limit for spin density on Fe3+ was estimated to be about 0.63. The hyperfine interaction constants on the pyrrole nitrogens (on average, ∼3.3 MHz) were also evaluated. The overall spin density distribution obtained was found to be in agreement with that estimated theoretically (Ghosh, A.; Gonzalez, E.; Vangberg, T. J. Phys. Chem. B 1999, 103, 1363) using density functional theory.