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 2 A 1u and one of 2 A 2u symmetry are both examined for each of these systems. The 2 A 1u cations are calculated to lie lower in energy than the 2 A 2u 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 2 A 1u species is predicted to consist of three separate bands decreasing in intensity with increasing energy, while that of the 2 A 2u 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 2 A 1u ions is dominated by one transition, while at least three strong bands are calculated in the Soret region for the 2 A 2u ions, again in reasonable accord with experiment. Charges, ionization energies, and spin densities are reported and discussed for all compounds.