An Estimation Method of Metal-Ligand Orbital Mixing in Lanthanide(III) Complexes Using Magnetic Circular Dichroism

The photophysical properties of lanthanide(III) complexes depend on the magnitude of orbital mixing between the lanthanide(III) and ligands. Herein, an estimation method of orbital mixing in lanthanide(III) complexes is reported using LnCl(3)nH(2)O (Ln = Pr, Gd, Tb) and Ln(tfa)(3)(H2O)(2) (tfa: trifluoroacetylacetonate, Ln = Pr, Gd, and Tb) for the first time. The electronic state properties were assessed from the electronic absorption and magnetic circular dichroism (MCD) spectra. The MCD spectra revealed the energy levels of the spin-allowed and spin-forbidden 4f-5d transitions of the Tb(III) complex that is hidden by the intense pi-pi* transition of the ligands. This energy gap corresponds to the exchange splitting energy between the 5d and 4f(n-1) electrons, which provides information regarding the orbital mixing between the Tb(III) ion and the ligands.