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