Ab Initio Calculation of the Electronic Structure and Spectrum of Co(NH3)63+; Comparisons with Isoelectronic CoF63−

Hartree—Fock—Roothaan LCAO MO SCF calculations, with the fixed core approximation plus limited configuration interaction, are reported for the ground and some excited states of Co(NH3)63+. Results are discussed with respect to the effects of ligand—ligand interaction, varying the radial part of the Co 3d AO basis functions, maintaining orthogonality of ligand t1u and a1g symmetry orbitals to Co 3s and 3p orbitals, and including configuration interaction. The calculated d—d excitation energies agree very well with experiment, and a reasonable binding energy is estimated. These results are contrasted with previous calculations on CoF63− to analyze how the metal—ligand interaction differs between the so-called ``covant'' and ``ionic'' cases. An analysis of why 1A1g is the ground state for the NH3 complex and 5T2g is the ground state for the F− complex is given along with a discussion of the parameter 10Dq.