Valence-states in titanium and vanadium
1958; Pergamon Press; Volume: 7; Issue: 1-2 Linguagem: Inglês
10.1016/0022-1902(58)80021-4
ISSN1878-1225
Autores Tópico(s)Crystallography and molecular interactions
ResumoThe energies of excitation from the ground-state to the valence-states deriving from the configurations d5, d4s, d4p, d3sp, d3p2, d2sp2, d2p3, and dsp3, of vanadium, and to the valence-states deriving from d4, d3s, d3p, d2sp, d2p2, dsp2, dp3, and sp3 of titanium, have been calculated on the basis of the Slater-Condon theory of atomic spectra, using empirically determined atomic spectral parameters. The relative suitability of each of these alternative valence-states towards the formation of compounds VX5, and TiX4, has been assessed from consideration of the excitation energies required, the “bonding-power” of the orbitals, and the geometric stability of the molecular structure formed. It is concluded that the favoured structures are the trigonal bipyramid for VX5 (deriving essentially from the d3sp configuration of V), and the tetrahedral structure for TiX4 (deriving essentially from the d3s configuration of Ti). However, it appears that a vanadium atom in an “isovalent hybrid” configuration, obtained by admixing d3sp with dsp3, has greater “bonding power” than either of the pure configurations. Similarly, the admixture of d3s with sp3 in titanium results in a tetrahedral atom of enhanced orbital bonding power. The mixing process requires a promotional energy, but substantial increases in orbital bonding power result from a small amount of isovalent hybridization, for which the cost in energy is comparatively minor. The variable dissociation energies in the stepwise disruption of TiCl4 are tentatively discussed in relation to proposed valence configurations of Ti in TiCl4, TiCl3, TiCl2, and TiCl. It is suggested that the excitation energies to reach the valence-states fall along the series TiCl4 → TiCl, and that, simultaneously, the effective electronegativity of the Ti atom decreases.
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