Although the optical spectra of LnCl₆⁹– systems are complex, only two crystal field parameters, B₄₀ and B₆₀, are required to model the J-multiplet crystal field splittings in octahedral symmetry. It is found that these parameters exhibit R–⁵ and R–⁷ dependence, respectively, upon the ionic radius Ln³+(VI), but not upon the Ln–Cl distance. More generally, the crystal field strengths of LnX₆ systems (X = Br, Cl, F, O) exhibit linear relationships with ligand electronegativity, charge transfer energy, and fractional ionic character of the Ln–X bond. Copyright © 2013 American Chemical Society.
crystal field theory