Electronic structure of homoleptic transition metal hydrides: TiH4, VH4, CrH4, MnH4, FeH4, CoH4, and NiH4

Abstract

A b initio molecular electronic structure theory has been applied to the family of transition metal tetrahydrides TiH4 through NiH4. For the TiH4 molecule a wide range of contracted Gaussian basis sets has been tested at the self-consistent-field (SCF) level of theory. The largest basis, labeled M(14s 11p 6d/10s 8p 3d), H(5s 1p/3s 1p), was used for all members of the series and should yield wave functions approaching true Hartree-Fock quality. Predicted SCF dissociation energies (relative to M+4H) and M–H bond distances are TiH4 132 kcal, 1.70 Å; VH4 86 kcal, 1.64 Å; CrH4 65 kcal, 1.59 Å; MnH4 – 36 kcal, 1.58 Å; FeH4 0 kcal, 1.58 Å; CoH4 27 kcal, 1.61 Å; and NiH4 18 kcal, 1.75 Å. It should be noted immediately that each of these SCF dissociation energies will be increased by electron correlation effects by perhaps as much as 90 kcal. For all of these molecules except TiH4 excited states have also been studied. One of the most interesting trends seen for these excited states is the shortening of the M–H bond as electrons are transferred from the antibonding 4t2 orbital to the nonbonding 1e orbitals.