Lanthanide(III) Complexes Based on Tris(2-pyridyl)phosphine Oxide: First Examples

A series of mononuclear complexes [Ln(Py₃PO)₂(NO₃)₃]·1.5Me₂CO (Ln = Sm, Eu, Gd, Tb, Dy) and [Ln(Py₃PO)(TTA)₃] (Ln = Eu, Tb; TTA^‒ is thenoyltrifluoroacetonate ion) based on tris(2-pyridyl)phosphine oxide (Py₃PO) is synthesized and studied. In the synthesized compounds, Py₃PO acts as a N,O-chelating ligand resulting in the formation of coordination polyhedra N₂O₈ and NO₇ of the Ln atom in complexes [Ln(Py₃PO)₂(NO₃)₃]·1.5Me₂CO and [Ln(Py₃PO)(TTA)₃], respectively. The complexes of Sm³⁺, Eu³⁺, Tb³⁺, and Dy³⁺ ions exhibit lanthanide-centered photoluminescence in the solid phase at 300 K. The energy of the T₁ triplet level of Py₃PO is determined to be 21 900 cm^‒1 from the ligand-centered phosphorescence spectrum of the Gd(III) complex at 77 K. Among the complexes with the \({\text{NO}}_{3}^{ - }\) ions, Py₃PO exhibits the highest sensitizing ability toward Tb³⁺, whereas the ligand environment in the complexes with the TTA^‒ ions most efficiently sensitizes the Eu³⁺ ion luminescence.