Quantum-chemical analysis of electronic structure of hemochromes and parameters of their Mössbauer spectra

Results are presented from quantum-chemical calculations of the electronic structure and parameters of the Mossbauer spectra of low-spin (S=1/2) six-coordinated ferriporphyrin complexes with axial ligands in which there are cyanide (CN) and/or pyridine (Py) ligands. On the basis of quantum-chemical calculations, a theoretical explanation has been obtained for the experimentally observed relationship of an anomalous decrease in values of quadruple splitting when the Py ligand is replaced by CN. It is tentatively concluded that2Eg is the ground term in these hemochromes. In this state, the unpaired electron occupies symmetrically the dπ (dxz, dyz) orbitals of the Fe iron.