The ligand dependence of lanthanide 4f → 4f magnetic dipole transition moments

Publisher Website
Google Scholar
Abstract
The magnetic‐dipole moments associated with 4f → 4f radiative transitions in lanthanide complexes are usually calculated on the basis of a static crystal‐field model in which the ligands’ influence is confined to mixing (and splitting) the 4fN eigenstates of the ‘‘free’’ lanthanide ion. In this model the ligand charge distributions are assumed to be passive to the radiation field, with the latter acting only on the ligand‐perturbed 4fN states of the lanthanide ion. Here we consider another model in which the ligand charge distributions are assumed to be polarized by the radiation field and then coupled to 4f → 4f electric‐multipolar transition moments to effect a resonant magnetic‐dipole interaction with the radiation field. This model (or mechanism) is exactly analogous to the dynamic‐coupling (or ligand‐polarization) model described previously for lanthanide 4f → 4f electric‐dipole transition moments [see, for example, J. Phys. Chem. 8 8, 3579 (1984)]. It is shown that the dynamic‐coupling (DC) mechanism for 4f → 4f magnetic‐dipole transition moments will be competitive with the static‐coupling (SC) mechanism only for transitions with strong ‖ΔJ‖>1 character, and even for these transitions the DC contributions to total magnetic‐dipole strength are predicted to be small (−7 D2). However, it is also shown that the DC contributions to the electric‐ and magnetic‐dipole transition moments of 4f → 4f transitions in chiral lanthanide systems may be crucial to explaining (or rationalizing) the rotatory strengths of these transitions. The latter suggestion is especially applicable to transitions whose intensities are known to be hypersensitive to the ligand environment.