Synthesis, crystal structure, and luminescence properties of rare-earth complexes with 2,2′-bis[(diethylcarbamoyl)- methoxy]-1,1′-biphenylene

Abstract

A new amide-based ligand derived from biphenyl, 2,2′-bis[(diethylcarbamoyl)-methoxy]-1,1′-biphenylene (L), and its complexes of rare-earth picrates were synthesized. Solid complexes of lanthanide picrates (Ln = La, Nd, Eu, Gd, Tb, and Y) with this new ligand were prepared and characterized by elemental analysis, conductivity measurements, X-ray powder diffraction, and infrared spectroscopies. The molecular structure of [Gd(pic)₃L] shows that the Gd(III) is eight-coordinate by four oxygen atoms from L and the other from one bidentate and two unidentate picrates. Furthermore, [Gd(pic)₃L] units are linked by intermolecular hydrogen bonds to generate a 2-D netlike supramolecule. Under excitation, the Eu(III) complex exhibited characteristic emissions of europium. The luminescence properties of the Eu(III) complex in solid state and in CHCl₃, acetone, acetonitrile, and DMF were investigated. The lifetime of the ⁵ D ₀ level of Eu(III) in the complex was 0.26 ms. The quantum yield Φ of the europium picrate complex was 6.67 × 10⁻³ with quinine sulfate as reference. The lowest triplet state energy level of the ligand indicates that the triplet state energy level of the ligand matches better to the resonance level of Eu(III) than Tb(III).

Keywords:

• Rare-earth picrate complexes
• Crystal structure
• Hydrogen bonds
• Luminescence properties

Acknowledgments

The authors acknowledge the National Natural Science Foundation of China Research (Grants 20771048 and 20621091) and the Fundamental Research Funds for the Central Universities (Grant Nos lzujbky-2010-27 and lzujbky-2010-29) for the financial support.