On the bonding to transition metal atoms in low oxidation states

Abstract

Ab initio spin-coupled calculations have been carried out on MH and MH+ species to investigate the electronic structure of systems containing transition metal atoms in low oxidation states; results are presented for VH, where the bonding can be understood in terms of the overlap between a 'bonding hybrid' on vanadium and a distorted Is function on hydrogen.

Bond formation in diatomic transition metal hydrides: Insights from the analysis of domain‐averaged fermi holes

“…A key factor in determining the ground state symmetries of the various MH + cations is the distribution of electrons in the various nonbonding transition metal d orbitals, so as to minimize the overall electron repulsion. SC calculations for MH + (M = Sc–Cr, Y–Mo) cations produced much the same description and, moreover, a very similar picture also emerged for the corresponding neutral species 63–65. In general, the additional electron in the neutral species near equilibrium geometry occupies a nonbonding σ‐symmetry orbital, directed away from the MH bond.…”

“…Our motivation for selecting the particular systems that we study here can be traced back to a series of generalized valence bond (GVB) studies,57–62 which provided a very appealing qualitative model of the chemical bonding in diatomic transition metal hydride cations MH + near equilibrium geometry. Spin‐coupled (SC) calculations, which relaxed certain orbital‐orthogonality and spin‐pairing restrictions in the GVB treatment, provided a very similar picture for the bonding in MH + cations (M = Sc–Cr, Y–Mo) near equilibrium geometry and, moreover, for the corresponding MH neutral species near equilibrium geometry 63–65. Additionally, and of particular relevance to this work, the SC calculations provided a useful qualitative description of the geometry dependence of the bonding in these MH neutral species 63–65…”

“…Spin‐coupled (SC) calculations, which relaxed certain orbital‐orthogonality and spin‐pairing restrictions in the GVB treatment, provided a very similar picture for the bonding in MH + cations (M = Sc–Cr, Y–Mo) near equilibrium geometry and, moreover, for the corresponding MH neutral species near equilibrium geometry 63–65. Additionally, and of particular relevance to this work, the SC calculations provided a useful qualitative description of the geometry dependence of the bonding in these MH neutral species 63–65…”

“…All of the CASSCF calculations were carried out in C 2 v symmetry, using state averaging of the two degenerate roots for the cases with spatially degenerate states (Δ or ϕ). For convenience, we chose to use the same Cartesian gaussian basis sets of TVZP quality (originally taken from GAMESS—UK77) as in the SC calculations on these various systems 63–65…”

“…The main purpose of this article is to examine the geometry dependence of the bonding in transition metal hydrides MH (M = Sc–Cr) from the perspective of DAFH analysis 44–49. So as to allow a proper comparison with the earlier GVB57–62 and SC calculations,63–65 we first apply DAFH analysis to the MH + cations (M = Sc–Cr) near equilibrium geometry. The same analysis was then applied to the description of the neutral hydrides ScH ( 1 Σ + ), TiH ( 4 ϕ), VH ( 5 Δ), and CrH ( 6 Σ + ), initially at the same geometry, but the main attention was then focused on the description of the geometry dependence of the bonding in each of these systems.…”