Electronic structure and spatial arrangement of C2v-coordinated ferric iron in metmyoglobin, metmyoglobin fluoride, and methemoglobin.

The electronic term scheme of ferric iron in metmyoglobin, metmyoglobin fluoride, and methemoglobin is evaluated by a Hamiltonian which involves the Coulomb repulsion of the 3d electrons, their interaction with the C2v-coordinated ligands, and spin-orbit coupling. The adjustable parameters of the theory were determined by a least squares fit to experimental EPR, susceptibility, and far-infrared data reported in the literature. According to these results, the structural properties of the ferric ion and its neighboring ligands were discussed by means of group theoretical arguments: An increasing out of plane position of the ferric ion is found in the sequence metHb--metMb--MbF which corresponds to an increasing binding strength with the axial ligands.