Theoretical Study of the Molecular Properties of Cerium Trihalides and Tetrahalides CeXn (n = 3, 4; X = F, Cl)

Abstract

Relativistic effective core potential quantum chemical investigations of molecular geometries, vibrational frequencies, and bond dissociation energies of cerium tri- and tetrahalides CeX3 and CeX4 (X = F, Cl) are presented. At RHF, MP2, and CASSCF levels of theory, CeF4 and CeCl4 possess stable tetrahedral (Td) geometries, and the calculated bond distances and vibrational frequencies lie very close to available electron diffraction and vibrational spectroscopy data. There is evidence of different stabilities of present tetrahalides toward the reductive elimination to CeX3. Thus, the very strong CeF3−F bond can be contrasted with the easier chlorine elimination to CeCl3. Five possible lower-lying electronic states are associated with open-shell CeX3 halides, depending on the 4f orbital occupancy. The (4fz3)1 configuration represents the ground state, mostly due to the nonbonding nature of the corresponding atomic orbital whose electron density, perpendicular to the molecular plane, minimizes the electrosta...