Calculation of the electronic structure of metalloporphyrin dianions by the restricted Hartree-Fock method

Abstract

The metalloporphine dianions (Me-P)2− with D4h symmetry for the nuclear skeleton have an eg2 electronic configuration, which generates the triplet state 3A2g and the three single states 1B1g, 1B2g, and 1A1g. With the aid of projection operators of the symmetry group, SCF equations have been formulated for such systems with open shells of degenerate orbitals, where the Roothaan method is not directly applicable. Calculations of the individual states of (Me-P)2− and its analogs have been performed by the proposed method in the π-electronic approximation. In accordance with Hund's rule, it has been found that the lowest level in the multiplet is the triplet level and that the subsequent singlet levels of (Me-P)2− are 340 (1B1g), 2560 (1B2g), and 3010 (1A1g cm−1 above it. A comparison of the π-electron densities of (Me-P)2− and Me-P has revealed, first, that the additional charge is distributed along the periphery of the macrocycle (the maximum increase takes place at the bridging atoms) and, second, that a number of bonds are strengthened, rather than weakened. The results obtained correlate well with the data on the reactivity and vibrational spectra of the dianions of porphyrins.