Molecular Ladders of Lanthanide-3-phenyl-4-benzoyl-5-isoxazolonate and Bis(2-(diphenylphosphino)phenyl) Ether Oxide Complexes: The Role of the Ancillary Ligand in the Sensitization of Eu3+ and Tb3+ Luminescence

Three new lanthanide heterocyclic β-diketonate complexes having the general formula Ln(PBI)3(DPEPO) [HPBI = 3-phenyl-4-benzoyl-5-isoxazolone, DPEPO = bis(2-(diphenylphosphino)phenyl) ether oxide and Ln3+ = Eu3+ (1), Tb3+ (2), and Gd3+ (3)] have been synthesized. Compounds 1 and 2 were characterized by single-crystal X-ray diffraction. The single-crystal X-ray diffraction analyses of 1 and 2 revealed that these complexes are mononuclear, and that the central Ln3+ ion is coordinated by six oxygen atoms furnished by three bidentate β-diketonate ligands and two oxygen atoms from the bidentate DPEPO ligand. The overall molecular geometry is distorted square prismatic. Examination of the packing diagrams for 1 and 2 revealed the presence of interesting molecular ladder structures held together by π···π and intermolecular hydrogen-bonding interactions. The effect of the chelating ancillary phosphine oxide ligand DPEPO on the sensitized luminescence of Eu3+ and Tb3+ luminescence in these heterocyclic β-diketonate complexes has been investigated. The ancillary ligand increases considerably the luminescence efficiency of [Eu(PBI)3(DPEPO)] (overall quantum yield 2−30%; 5D0 lifetime 250−1056 μs) compared to Eu(PBI)3(C2H5OH)(H2O), through the formation of intraligand states, while it is detrimental to Tb3+ luminescence in [Tb(PBI)3(DPEPO)] (overall quantum yield 11 to 0.5%; 5D4 lifetime 400 to 168 μs).