A theoretical study of the electronic structure and spectra of metalloporphine cations

A theoretical study is made of the electronic spectra of Mg(II), Zn(II), and Co(III) porphine and their π cations using the INDO/S-CI spectroscopic model. The calculated electronic spectra for the neutral compounds compare well with experiment. The two low-lying π cations, one of 2A1u and one of 2A2u symmetry are both examined for each of these systems. The 2A1u cations are calculated to lie lower in energy than the 2A2u cations by only 4 kcal/mol, consistent with the findings that both ions are found depending on substituents and solvent.The visible region of the spectrum of the 2A1u species is predicted to consist of three separate bands decreasing in intensity with increasing energy, while that of the 2A2u species is calculated to consist of three allowed transitions of near equal intensity, in agreement with experimental findings. In general the Soret region of the 2A1u ions is dominated by one transition, while at least three strong bands are calculated in the Soret region for the 2A2u ions, again in reasonable accord with experiment. Charges, ionization energies, and spin densities are reported and discussed for all compounds.