Luminescent Binuclear Eu(III) and Tb(III) Complexes Based on 3,6-bis(Diphenylphosphinyl)Pyridazine

Isostructural binuclear complexes [Ln₂L₂(hfac)₆] (Ln = Eu, Tb; hfac^– = hexafluoroacetylacetonate ion) are synthesized by the interaction of [Ln(hfac)₃(H₂O)₂] with 3,6-bis(diphenylphosphinyl)pyridazine (L). According to the single-crystal XRD data, two Ln(hfac)₃ moieties in the complexes are connected by two O,O´-bidentate-bridging ligands L, and the coordination polyhedron Ln@O₈ has the geometry of a triangular dodecahedron. The Eu³⁺ and Tb³⁺ complexes exhibit characteristic lanthanide-centered photoluminescence in the solid state at 297 K with luminescence quantum yields of 31% and 2% and excited state lifetimes of 707 and 30 μs, respectively, thus indicating that luminescence sensitization by the ligand environment is more effective for Eu³⁺ than for Tb³⁺.