Systematic Behavior of Charge-Transfer Transitions and Energy Level Variation in Soft Donor Complexes of the Trivalent Lanthanides

The systematic behavior of the charge-transfer (CT) energies in mixed 2,2‘-bipyridyl (bipy), N,N-diethyldithiocarbamate (Et2dtc-) complexes of the trivalent lanthanides, Ln(Et2dtc)3(bipy), is investigated to
understand the electronic structure of f-element complexes containing soft donor ligands. The energies of
ligand to Ln3+ CT are extremely low in this system, an effect attributed to the presence of the soft donor
ligands. The lowest CT energy level for the Sm3+, Eu3+, and Yb3+ complexes falls into the visible range. In
Eu(Et2dtc)(bipy), the Eu3+ ion becomes nonluminescent because the CT energy stretches below the metastable
5D0 electronic state, whereas luminescence from the CT state and the 4f13 2F5/2 state are observed in the Yb
compound. The variation in the energy of the lowest level CT transition for the entire Ln(Et2dtc)3(bipy)
series has been evaluated using the experimentally determined CT levels of the Sm3+, Eu3+, and Yb3+
compounds based on the systematic behavior of the lanthanides, which is invariant with respect to the type
of ligand. The energy difference between the ground electronic states of the lanthanide ions and the ligand-centered valence band may also be calculated from these results.