Synthesis, Structural Characterization and Chiroptical Studies of Bidentate Salen-Type Lanthanide (III) Complexes

The salen-type ligand prepared with (R,R) diphenylethan-1,2-diamine and salicylaldehyde provides stable and inert complexes KLnL2 upon simple reaction with lanthanide halides or pseudohalides LnX3 (Ln = Tb3+-Lu3+; X=Cl or TfO) of its potassium salt. All the complexes were completely characterized through nuclear magnetic resonance (NMR), electronic circular dichroism (ECD) in the UV and some (Er3+, Tm3+, Yb3+) also with Near-IR ECD (NIR-ECD) and luminescence (Tb3+, Tm3+). Careful analysis of the NMR shifts demonstrated that the complexes are isostructural in solution and afforded an accurate geometry. This was further confirmed by means of Density Functional Theory (DFT) optimization of the Lu3+ complex, and by comparing the ligand-centered experimental and time-dependent TD-DFT computed UV-ECD spectra. As final validation, we used the NIR-ECD spectrum of the Yb3+ derivative calculated by means of Richardson’s equations. The excellent match between calculated and experimental ECD spectra confirm the quality of the NMR structure.