Pulsed EPR characterization of the low-spin iron(III) porphyrinate complexes with phenyl isocyanide ligands having the dxy orbital ground state

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 d(xy) orbital configuration. The spin density distribution in the porphyrin pi system was obtained, with major spin density (similar to0.06) being delocalized to each meso carbon atom. The spin density on the pyrrole beta 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, similar to3.3 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.