Abstract:
The luminescence properties of the three new stoichiometrically mixed lanthanide complexes, Sm(1/2)Eu(1/2)(PBI)(3)center dot bpy center dot H(2)O (1), Sm(1/2)Tb(1/2)(PBI)(3)center dot bpy center dot H(2)O (2) and Eu(1/2)Tb(1/2)(PBI)(3)center dot bpy center dot H(2)O (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)center dot bpy center dot H(2)O (4), Eu(PBI)(3)center dot bpy center dot H(2)O (5) and Tb(PBI)(3)center dot bpy center dot H(2)O (6). Compound 5 was structurally characterized by single-crystal X-ray diffraction, and crystallizes in the triclinic space group P (1) over bar with a = 12.839(3) angstrom, b = 13.863(3) angstrom, c = 16.379(3) angstrom, alpha = 81.66(3)degrees angstrom, beta = 73.32(3)degrees , gamma = 89.26(3)degrees and V = 2762.0(10) angstrom(3). The crystal structure of 5 comprises an assembly of mononuclear species, each of which features a central Eu(3+) 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 pi-pi, 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.
