Electronic structure and bonding in metal porphyrins, metal=Fe, Co, Ni, Cu, Zn

A systematic theoretical study of the electronic structure and bonding in metal meso-tetraphenyl porphines MTPP, M=Fe, Co, Ni, Cu, Zn has been carried out using a density functional theory method. The calculations provide a clear elucidation of the ground states for the MTPPs and for a series of [MTPP]x ions (x=2+, 1+, 1−, 2−, 3−, 4−), which aids in understanding a number of observed electronic properties. The calculation supports the experimental assignment of unligated FeTPP as A2g3, which arises from the configuration (dxy)2(dz2)2(dxz)1(dyz)1. The calculated M–TPP binding energies, ionization potentials, and electron affinities are in good agreement with available experimental data. The influence of axial ligands and peripheral substitution by fluorine are in accord with the experimental observation that not only half-wave potentials (E1/2) of electrode reactions, but also the site of oxidation/reduction, may be dependent on the porphyrin basicity and the type of axial ligand coordination.