ELECTRONIC STRUCTURE AND BONDING IN THE $FeF_{s}$ SYSTEM$^{\ast}$

$^{\ast}$ Supported by the Advanced Research Projects Agency (SD-102).Author Institution: Department of Chemistry, Purdue UniversityDespite the tremendous success of semiempirical ligand (or crystal) field theory in interpreting the energy states of transition-metal compounds, the encompassing Molecular Orbital (MO) approach has long been recognized as a better conceptual basis for the general theory. It allows for experimentally detected electronic delocalization and for established correlations with chemical properties of the ligands. Because of the complexity of the system, however, direct theoretical calculation is difficult. The discrete complex $FeF_{s}$ has been treated according to conventional LCAO---MO---SCF theory based upon the 2s and 2p fluorine orbitals and the $3d, 4s, 4p$ and 4d metal orbitals, suitably orthogonal to inner orbitals on the same center. Inner-shell electrons are assumed to furnish a constant coulomb-exchange potential; multicentered integrals have been approximated. Despite the complexity of the calculation, the results are in reasonable accord with experiment. The following points will be discussed: energies of the ground and lower excited states; electron delocalization; nature of the participation of the fourth-quantum orbitals; and an assessment of the approximations made