Ab initio calculations on first-row transition metal porphyrins. Part 1. Geometrical details, charge distributions and the effects of additional charge

Abstract

Ab initio calculations were done on eight first-row transition-metal porphyrins and dihydrogen porphyrin. The metal ions situated in the centre of the porphyrins were: chromium(III), manganese(III), iron(III), cobalt(III), cobalt(II), nickel(II), copper(II) and zinc(II). A chlorine counter ion was included in order to keep the molecules containing metal(III) ions neutral. The optimal geometries and charge distributions were calculated with the restricted Hartree-Fock routines and distributed multipole analysis routines present in gamess-uk. The metal atoms, the nitrogen atoms and the chlorine atoms were described using the SV-3-21G basis set and the carbon and hydrogen atoms with STO3G. The effect of additional charge on the molecules was estimated by removing one electron from the HOMO or adding one to the LUMO of each compound. The porphyrin charge distributions assume the shape of concentric rings of alternating sign. They provide the molecules with the ability to preserve a remarkably high charge on the central metal ion. This enables the occurrence of stable metal ions in an apolar environment that are still accessible because of the planar geometry of the porphyrin moieties.