Synthesis, Structure And Properties Of Rare Earth Carboxylic Acid Complexes

The binary and the ternary Sm(III) complexes, NaSm(Sal)4(H2O)2 and NaSm(Sal)4(Phen)2, with the salicylic acid (HSal) and o-phenanthroline (Phen) have been prepared, respectively. They are confirmed by elemental analysis and the spectra of IR, and UV-vis and the thermal analysis. The photoluminescence intensity of the complex NaSm(Sal)4(Phen)2 is enhanced by more than two hundred times with respect to that of the binary complex NaSm(Sal)4(H2O)2. The second ligand Phen shows enhancement effect on the fluorescence of the complex NaSm(Sal)4(Phen)2. This is due to the reasons of both the presence of O-H vibrations in the complex NaSm(Sal)4(H2O)2, which contribute to non-radiative deactivation of the 4G5/2 emitting state of the Sm3+ ion and the increase in molecular rigidity through the introduction of Phen in the complex NaSm(Sal)4(Phen). On the other hand, the introduction of Phen into the coordination sphere may result in a more asymmetric coordination geometry than that of the NaSm(Sal)4(H2O)2 composite. The formation of an unique asymmetric environment surrounding the Sm 3+ ion leads to an increased transition probability for the fluorescence, and results in greatly enhanced fluorescence of the Sm3+ ion. The TG curves of the complexes NaSm(Sal)4(Phen) and NaSm(Sal)4(H2O)2 present weight losses in temperature 239.2 and 177.6 ℃ , respectively, indicating that the thermal stability of the former is higher than that of the latter.The crystal structure of NaSm(Sal)4(Phen)2 was determined by X-ray diffraction. The crystal is monoclinic, space group C2/c with cell dimensions of a = 28.4989 (7) A, b = 9.3347 (2) A, c = 22.7954 (5) A, p = 132.4010 (8)° ,V= 4478.1(2) A3, Z = 4,μ (Mo Kα) = 13.97 cm-1, Dc = 1.605 g/cm3. The structure was solved by direct methods and refined on F2 by full-matrix least-squares methods using DIRDIF-99 program. The refinement converged at R = 0.021 and wR = 0.045 for 3612 observed reflections with I > 2σ(I). Each carboxylate group acts as a bridging ligand between the Na ionand Sm, via the carboxylate O atoms. Each Sm atom is coordinated by four N atoms of two phenanthroline (phen) ligands and four O atoms of four carboxylate groups, which further coordinate to two neighboring Na atoms, forming a one-dimensional chain structure.A series of dinuclear complexes of salicylic acid (HSal) and o-phenanthroline (Phen) with different molar ratios of Eu3+ to Y3+ have been synthesized. They are confirmed by elemental analysis and the spectra of IR, and UV-vis and the thermal analysis. Their compositions are Eu xY1-x (Sal)3(Phen) (x=0.1-1.0). Enhancement of Eu3+ fluorescence in Eu-complexes has been observed by the addition of Y3+ and the luminescence intensity reaches maximum which is nearly eight times as high as that of the complex Eu (Sal)3(Phen) when the molar ratio of Eu3+: Y3+ = 0.6 : 0.4. The fluorescence enhancement is concerned with both the structure of the complexes and the intramolecular energy transfer. When the excitation energy is absorbed by the ligands, the energy is transferred to the 5D0 energy level of the Eu3+ ion, and the photons are emitted when the ions relax from the 5Do level to the 7F J (where J = 1, 2 and 4) level, which accounts for the bands observed. While the Y-complexes do not show any luminescence at all owing to the fact that the yttrium ion has no 4f electrons and its emitting level is at higher energy than the triplet level of the ligands. As a result, the energy absorbed by the ligands which coordinate with the yttrium ions is transferred to the europium ions and therefore the luminescence intensity of the Eu-complexes enhances due to cofluorescence.Through the introduction of the complexes Eu(Sal)3(Phen) and Eu(TTA)3(Phen) with the mass percent of 0.2% into the PE resin, the light conversion films PEa and PEb have been synthesized respectively. It is observed that the complexes still possess fluorescence when they were processed in films, though the mechanical properties of the light conversion films have been decreased slightly compared to the checked film. The ligh...