R. Zwaans et al., AB-INITIO CALCULATIONS ON FIRST-ROW TRANSITION-METAL PORPHYRINS .1. GEOMETRICAL DETAILS, CHARGE-DISTRIBUTIONS AND THE EFFECTS OF ADDITIONALCHARGE, Journal of molecular structure. Theochem, 339, 1995, pp. 153-160
Ab initio calculations were done on eight first-row transition-metal p
orphyrins and dihydrogen porphyrin. The metal ions situated in the cen
tre of the porphyrins were: chromium(III), manganese(III), iron(III),
cobalt(III), cobalt(II), nickel(II), copper(II) and zinc(II). A chlori
ne counter ion was included in order to keep the molecules containing
metal(III) ions neutral. The optimal geometries and charge distributio
ns were calculated with the restricted Hartree-Fock routines and distr
ibuted multipole analysis routines present in GAMESS-UK. The metal ato
ms, 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 ri
ngs of alternating sign. They provide the molecules with the ability t
o preserve a remarkably high charge on the central metal ion. This ena
bles the occurrence of stable metal ions in an apolar environment that
are still accessible because of the planar geometry of the porphyrin
moieties.