[Study on synthesis, structure characterization and fluorescence of europium complexes of 2-(4-fluorobenzoyl) benzoic acid].

The present paper reports three new europium complexes, EuL3(H2O)6, EuL3Phen(H2O)4 and EuL3 (TPPO) (H2O)5, synthesized with Eu(NO3)3 x 6H2O, 2-(4-fluorobenzoyl) benzoic acid, Phen and TPPO(L = 2-(4-fluorobenzoyl) benzoic acid, Phen = 1, 10-phenanthroline, TPPO = triphenyl phosphine oxide). Their composition and chemical structures were characterized by elemental analysis, IR and 1H NMR spectroscopy. The IR spectra indicated that all complexes exhibited the characteristic peaks of carboxylate, asymmetric stretching vibration (vas (CO2(- and symmetric stretching vibration (vs (CO2(- peaks; the C = O stretching band at 1,692 cm(-1) of COOH and the O--H stretching band around 2,500-3,200 cm(-1) disappeared. All these complexes had a smaller Deltav(vas (CO2(-))-vs(CO2(- value than that of NaL, so the carboxylate groups coordinated with the europium ion in the form of bridging bidentate. In 1HNMR, the signals of hydrogen in 2-(4-fluorobenzoyl) benzoic acid became wide and shifted upfield, and those in Phen, TPPO shifted downfield. The excitation and emission spectra were recorded at room temperature. The excitation spectra showed that the optimum excitation peaks of these three complexes, EuL3 (H2O)6, EuL3Phen(H2O)5 and EuL3(TPPO)(H2O)5, were at 353.0, 355.0 and 357.0 nm, respectively. All these three complexes showed Eu3+ ion characteristic emission bands, the electron-dipole transition 5D0 --> 7F2 and magnetism dipole transition 5D0 --> 7F1; their emission peaks were at 596.0, 617.0; 596.0, 619.0; 595.0, 620.0 nm, and the relative intensities were 1.1, 8.6; 15.2, 100.0; 3.6, 23.2, respectively. The intensity of 5D0 --> 7F2 was stronger than that of 5D0 --> F1, which indicated that europium ions were at asymmetric center. The emission intensities of europium ions were greatly sensitized by Phen.