[Synthesis and fluorescence properties of europium complexes with 4-(4-pyridyl formoyl) benzoic acid].

Three new europium complexes, Eu(PFBA)3 (H2O)4, Eu(PFBA)3 Phen (H2O)3 and Eu(PFBA)3 TPPO (H2O)3, were synthesized using 4-(4-pyridyl formoxyl) benzoic acid (HPFBA), 1,10-phenanthroline (phen) and triphenyl phosphine oxide (TPPO) as the ligands. In the complexes, two characteristic absorption bands of HPFBA due to vO-H (3 000-2 200 cm(-1)) and v c=o (1 697 cm(-1)) disappear, the asymmetry stretching vibration v(as)(coo-) and symmetry stretching vibration v(s)(coo-) of carboxyl appear, and the deltav(v(as)(coo)) - v(s)(coo-)) values are all smaller than that of NaPFBA. The carboxyl group of the ligand HPFBA is dehydrogenated and coordinated to Eu3+ with a bidentate chelating mode. The fluorescence properties of the complexes were studied. Each complex shows five emission bands at about 583, 596, 618, 655 and 703 nm, which are assigned to the characteristic emission 5D0 --> -F(j) (J = 0, 1, 2, 3, 4) transitions of Eu3+, respectively. The fluorescence intensity becomes stronger after the addition of phen and TPPO, and TPPO is better, which is due to synergistic effect of the second ligands.