EPR studies on the high spin Fe III tetraphenylporphine with rhombic character, determination of zero-field splitting parameters from the middle kramers transition

Abstract

Electron paramagnetic resonance transitions (EPR) in the middle Kramers doublet is observed for the first time in the 6A 1 ground state of Fe (III) complex of tetraphenylporphine (TPP) diluted in the polycrystalline free base tetraphenylporphine (THHP 2). The system shows the EPR spectra and resulting from several distinct species of high spin (Fe (III) TPP with various degress of rhombicity. The middle Kramers as absorptions are in general of much weaker intensity than the corresponding lowest Kramers absorptions, and their g values show marked systematic deviations from the calculated first order prediction. The deviation can be explained by carrying the Zeeman perturbation to the third order. The analysis also rendered it possible to determine the zero-field parameters D and E separately. The results indicate the similarity in the crystal field of the present system with that of cyctochrome P450.