Dual emission from stoichiometrically mixed lanthanide complexes of 3-phenyl-4-benzoyl-5-isoxazolonate and 2,2′-bipyridine

Abstract

The luminescence properties of the three new stoichiometrically mixed lanthanide complexes, Sm_1/2Eu_1/2(PBI)₃·bpy·H₂O (1), Sm_1/2Tb_1/2(PBI)₃·bpy·H₂O (2) and Eu_1/2Tb_1/2(PBI)₃·bpy·H₂O (3) [HPBI = 3-phenyl-4-benzoyl-5-isoxazolone; bpy = 2,2′-bipyridine] have been compared with those of the analogous single lanthanide ion systems, Sm(PBI)₃·bpy·H₂O (4), Eu(PBI)₃·bpy·H₂O (5) and Tb(PBI)₃·bpy·H₂O (6). Compound 5 was structurally characterized by single-crystal X-ray diffraction, and crystallizes in the triclinic space groupP with a = 12.839(3) Å, b = 13.863(3) Å, c = 16.379(3) Å, α = 81.66(3)°, β = 73.32(3)°, γ = 89.26(3)° and V = 2762.0(10) ų. The crystal structure of 5 comprises an assembly of mononuclear species, each of which features a central Eu³⁺ cation coordinated to three bidentate PBI ligands, a bidentate bipy ligand, and a water molecule. The overall geometry of the nonacoordinate array is that of a distorted monocapped trigonal prism. The X-ray diffraction study of 5 also revealed many interesting π–π, interplanar and intermolecular hydrogen-bonding interactions. The mixed lanthanide complexes 1–3 exhibit interesting dual emissions in the visible region. The quantum yields and lifetime measurements for 1–3 support the premise that Ln → Ln energy transfer occurs in these mixed lanthanide systems, along with the usual ligand-to-metal triplet energy pathways.