Excited State Properties of Lanthanide(III) Complexes with a Nonadentate Bispidine Ligand

Eu-III, Tb-III, Gd-III and Yb-III complexes of the non-adentate bispidine derivative L-2 (bispidine= 3,7-diazabicyclo [3.3.1]nonane) were successfully synthesized and their emission properties studied. The X-ray crystallography reveals full encapsulation by the nonadentate ligand L-2 that enforces to all Ln(III) cations a common highly symmetrical capped square antiprismatic (CSAPR) coordination geometry (pseudo C-4v symmetry). The well-resolved identical emission spectra in solid state and in solution confirm equal structures in both media. As therefore expected, this results in long-lived excited states and high emission quantum yields ([(EuL2)-L-III](+), H2O, 298 K, tau = 1.51 phi = 0.35; [(TbL2)-L-III](+), H2O, 298 K, tau = 1.95 phi = 0.68). Together with the very high kinetic and thermodynamic stabilities, these complexes are a possible basis for interesting biological probes.

Automated summary

Eu-III, Tb-III, Gd-III, and Yb-III complexes of the non-adentate bispidine derivative L-2 were successfully synthesized and their emission properties studied. X-ray crystallography revealed a common highly symmetrical coordination geometry enforced by the nonadentate ligand L-2, leading to long-lived excited states and high emission quantum yields. These complexes, with very high kinetic and thermodynamic stabilities, may serve as a basis for interesting biological probes.