Bonding in the monochlorides and dichlorides of iron and cobalt

Abstract

The geometries, ground and low-lying excited states of FeCl₂, CoCl₂, FeCl and CoCl have been studied using local density functional calculations within the linear combination of Gaussian-type orbitals framework. The ground state of FeCl₂ is predicted to be ⁵Δ_g and that of CoCl₂ to be ⁴Σ_g^–. These ground states and the predicted order of the excited states require reassignments of the electronic spectra of these molecules. Cellular ligand-field analyses have been performed resulting in excellent agreement with the experimental transition energies. The ground states of FeCl and CoCl are predicted to be ⁶Δ and ³Σ^– respectively. The dissociation energies of these species have been determined and a comparison of the bonding in these electronically related molecules is presented. These lead to the prediction that the second chloride is bonded more strongly than the first in the dichlorides.