Ab initio molecular orbital calculations of the cobalt porphine complex. I. LCAO SCF MO calculation of low‐spin, high‐spin, and π‐ionized states of Co‐porphine

Ab initio LCAO SCF MO calculations are carried out on planar Co‐porphine with a basis set of roughly double zeta quality for Co and N and of single zeta quality for C and H. The net charge on Co and N and the overlap population between them are 1.78, −0.57, and 0.06, respectively, in the 2 A 1g , state, which is known to be the ground state by experiment. The bonding in this complex is thus largely ionic. The first and second calculated ionization potentials are 6.51 and 6.77 eV, respectively, and are in reasonable agreement with the observed ionization potentials of 6.44 and 6.62 eV for Ni‐tetraphenylporphine. CI calculations within the framework of the ligand field theory are also performed. The calculated order of the five lowest states is 4 B 2g ≈ 4 E g , 4 A 2g , 2 A 1g , 4 E g from below and is not in agreement with the semiempirical order of 2 A 1g ≈ 4 B 2G , 4 A 2g , 2 E g , 4 E g determined by Lin.