Comparison of calculated and experimental 4f → 4f intensity parameters for lanthanide complexes with isotropic ligands

Calculations of 4f → 4f electric dipole intensity parameters are reported for six different lanthanide (III) systems whose solid-state structures and optical spectra have been well characterized. In each case, the ligands are considered to have isotropic electronic charge distributions, and the 4f → 4f intensity parametrization is expressed in terms of the parameters Aλλ±1,p(λ=2, 4, and 6), which have been defined in a previous paper (see paper I). The calculations include contributions to these parameters from both the static-coupling and dynamic-coupling intensity mechanisms. Comparisons between the calculated and empirically determined signs of the Aλλ±1,p parameters suggest that, in most cases, the dynamic-coupling mechanism makes the dominant contributions to the Aλλ+1,p parameters. The empirically determined signs of the Aλλ−1,p parameters correlate with those calculated on the basis of the static-coupling mechanism. For isotropic ligands, the dynamic-coupling mechanism cannot contribute to the Aλλ−1,p parameters. Intrinsic intensity parameters, defined within the context of the mechanism-independent superposition model for lanthanide-ligand interactions, are also derived for each of the six systems examined here. These parameters, denoted herein as Āλλ±1, are defined to be independent of coordination number, coordination geometry, and lanthanide site symmetry.