Zero-Field Splitting, Magnetic-Field Energies, Effective Magnetic Moments, and Electric-Field Gradients in High-Spin Ferric Porphyrin Compounds

Recently, the lowest electronic energy intervals in a series of 10 related high‐spin ferric porphyrin compounds have been measured directly by far‐infrared spectroscopy. The zero‐field splitting obtained ranged from 9.3 to 33⁻¹. In the calculations described here, we have successfully explained all 10 of these observed values, using a strong crystal‐field model with tetragonal symmetry and spin‐orbit coupling of the sextet ground state to excited quartet and doublet states to all orders. To do this, we have used what we considered to be a physically reasonable and internally consistent variation of three crystal‐field parameters. The corresponding eigenfunctions of the three ${}^6{A}_1$ doublets were also calculated for all 10 compounds and very little spin mixing obtained. We have used these eigenfunctions for each compound to calculate the effective magnetic moments of the ferric ion as a function of temperature, the magnetic‐field energies of the three doublets both to first order and also allowing magnetic‐field mixing of all six ${}^{6}A$ states, and finally the electric‐field gradient at the ferric ion nucleus including both a lattice and valence electron contribution. All of these properties are discussed and the calculated results compared with experiments whenever possible. In most cases, the agreement with existing experimental data is quite good.