Bonding in the monochlorides and dichlorides of iron and cobalt

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 (5) Delta(g) and that of CoCl2 to be (4) Sigma(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 (6) Delta and (3) Sigma(-) 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.