Syntheses And Luminescence Of Diamine Bridged Bipicolinic Acids And Their Terbium Complexes

In this paper, three diamine bridged bipicolinic acids, which have N4O2co-ordination sites, were designed and synthesized. These three acids are as follows:1,2-bis（6-carboxypyridin-2-methylamino）ethane （H₂L¹）,1,3-bis（6-carboxypyridin-2-methylamino）propane （H₂L²）,1,2-bis（6-carboxypyridin-2-methylamino）cyclohexa-ne （H₂L³） and they were synthesized by using dimethyl pyridine-2,6-dicarboxylate as the initial raw material. The structures of target compounds were confirmed by infrared spectrum, nuclear magnetic resonance spectrum of¹H and¹³C, mass spectrometry and X-ray single crystal diffraction analysis et al.Binary complexes of Tb（Ⅲ） or Eu（Ⅲ） with H₂L¹-H₂L³and ternary complexes ofTb（Ⅲ） with H₂L¹-H₂L³and2,2’-bipyridine （or1,10-phenanthroline） were synthesized.The complexes were characterized by molar conductivity, IR spectrum,thermo-gravimetic analysis, elementary analysis and fluorescence spectrum. Theresults showed that all free ligands can emit fluorescence, all Eu（Ⅲ） complexes can’temit characteristic fluorescence of Eu（Ⅲ）, and all Tb（Ⅲ） complexes can emit strongcharacteristic fluorescence of Tb（Ⅲ） peaking at about545nm. These ligands areexcellent sensitizers to Tb（Ⅲ）, and they don’t change the positions of characteristicTb（Ⅲ） fluorescence emission. Different complexes have different luminescentproperty, which is probably caused duo to the difference of the plane rigid of theligands. Because the second ligands,2,2’-bipyridine or1,10-phenanthroline, have thestrong ability to absorb UV-light can replace the water molecules in complexes, thefluorescence intensities of the ternary complexes are much stronger than those of thebinary complexes. But they didn’t change the positions of characteristic fluorescenceemission of Tb（Ⅲ）.At last, Tb（Ⅲ） complexes doped with non-fluorescent rare earth ions (Y³⁺, Gd³⁺)or divalent metal ions (Zn²⁺, Mg²⁺, Cu²⁺) were synthesized. The complexes werecharacterized by IR spectrum, thermo-gravimetic analysis and fluorescence spectrum.By comparing of fluorescence spectra, it can be found that when mole ratio of centralTb（Ⅲ） ion and doping ions (Y³⁺, Gd³⁺) is7:3, the complexes have strongestfluorescence. Based on the previous research, an optimum ratio was presented. Aquaternary complex of terbium was synthesized by introducing yttrium as the dopingion and2,2’-bipyridine as the second ligand, and the properties of the complex were characterized. By comparison, we found that the fluorescence intensity of thequaternary complex was little larger than that of the ternary complex, but much largerthan that of the binary complex. In addition, it was also found that the complexesdoped with the divalent metal ions (Zn²⁺, Mg²⁺) also have the best ratio, and under thisratio the fluorescence intensity of the complex is the strongest. But when the transitionmetal ions (Cu²⁺) was doped, the fluorescence of the complexes was quenched.