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

Eu III , Tb III , Gd III and Yb III complexes of the nonadentate 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 the 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 ([Eu III L 2 ] + , H 2 O, 298 K, τ = 1.51ms, φ = 0.35; [Tb III L 2 ] + , H 2 O, 298 K, τ = 1.95ms, φ = 0.68). Together with the very high kinetic and thermodynamic stabilities, these complexes are a possible basis for interesting biological probes.