X-ray Spectroscopy of CeBr6(2-) and Comparisons to the Corresponding Chloride and Fluoride Complexes

Recent studies of lanthanide bonding have shown that small amounts of metal--ligand covalency can impact bond energies and cause magnetic behavior to deviate from the free ion values. Quantifying covalent bonding parameters is necessary to support the rational design of these properties for applications in energy and information science. Here, two measurements of f-electron occupancy in CeBr6(2-) are reported based on X-ray spectra at the Ce L3- and Br K-edges and compared to the corresponding results for CeF6(2-) and CeCl6(2-). These values allow for the estimation of average metal-ligand overlap integrals and covalent bond stabilization energy. For this series of compounds, overlap integrals and bond covalency are found to have opposing trends as the halide is varied. Finally, correlations between Ce(IV) L3-edge doublet splitting, nf, and LMCT energies are identified that may indicate significant mixing between the 4f and 5d orbitals in other, noncentrosymmetric Ce(IV) complexes.