DENSITY DISTRIBUTIONS AND CHEMICAL BONDING IN DIATOMIC MOLECULES OF TRANSITION METALS

Electronic charge density distributions calculated from truncated-matrix Hartree-Fock wave functions for isoelectronic TiO and ScF are analyzed in terms of the interpretive concepts of chemical bonding. The analyses are based on an examination of the spatial characteristics of the orbital charge density contour maps, the features of density difference diagrams which compare the molecular orbitale with covalent and lone-pair charge distributions, and on a study of charge-transfer populations and charge moments. An important aspect is the transformation of the canonical orbital basis to the intrinsic localized basis defined by Edmiston and Ruedenberg. With this transformation, the complicated shell structures are simplified to well-defined hybrid lone-pair functions and to bonding orbitale which involve hybrid combinations of the usual valence orbitale of the atoms. It is shown that both TiO and ScF may be considered to be molecules with triple bonds (σ2π4) of strong ionic character. The oxide, however, is about equally intermediate to a covalent or ionic molecule, whereas the fluoride is predominantly ionic.