The Investigation Into Luminescence And Magnetocaloric Effect Of Lanthanide Complexes Based On Acylhydrazone Schiff-base

The lanthanide elements have attracted considerable investigative attention of scholars due to their special electronic structure.More and more lanthanide luminescent materials and magnetic refrigeration materials have been reported.Environmental influence caused by the emission of greenhouse gases especially carbon dioxide has become a major global concern.With the increase of CO₂concentration in atmospheric,trying to fix CO₂ under mild conditions by lanthanide metal complexes and convert it into practical compounds becomes a significant project.In this dissertation,ten lanthanide complexes based on flexible acylhydrazone Schiff-base ligand andβ-diketonate co-ligand have been synthesized successfully.Especially,thestructuresandluminescence/near-infraredluminescence/magnetocaloric effect of these complexes have been investigated.The main works of this thesis are as follows:1.Four lanthanide complexes with novel structures have been synthesized successfully,[Eu₄（L）₄（CO₃）（acac）₂（H₂O）₂（CH₃OH）₂]·5H₂O·2CH₃OH（1）,[Gd₄（L）₄（CO₃）（acac）₂（CH₃OH）₄]·2CH₃OH·CH₂Cl₂（2）,[Tb₄（L）₄（CO₃）（acac）₂（H₂O）₂（CH₃OH）₂]·3H₂O·CH₃OH（3）,[Er₄（L）₄（CO₃）（acac）₂（H₂O）₂（CH₃OH）（DMF）]·H₂O·CH₃OH（4）.For complexes 1-4,by absorbing and fixing CO₂ spontaneously under atmospheric condition,CO₃^2-as a bridging tetradentate ligand,the four Ln ^IIIII ions are bridged by twoμ₂-O oxygen atoms from CO₃^2-to form a Ln₄ cluster.X-ray diffraction data reveals that the non-centrosymmetric（1,3 and 4）or centrosymmetric（2）unit has two distinct Ln ^IIIII ions,nine-coordinated Ln ^IIIII ions in distorted spherical capped square antiprism geometry and eight-coordinated Ln^IIIII ions in distorted triangular dodecahedron geometry.The structural distinction is on account of the different coordinated solvent molecules.Magnetic study indicates that complex 2 can act as cryogenic magnetic refrigerant and the magnetocaloric effect（MCE）was detected with the magnetic entropy change of-ΔS_m=21.43 J·kg^-1·K^-11 atΔH=7 T and 5 K,which is much smaller than the theoretical value.By comparing with those Gd-based clusters without the coordinated CO₃^2-,we infer that the coordination of CO₃^2-can influence the MCE,it makes an enhancement of antiferromagnetic coupling and leads to the reduction of MCE.The fluorescence properties of complexes 1 and 3 were also investigated.The results prove that the complex 3 can show Tb^IIIII characteristic emission peaks,while for complex 1,it exhibits several major emission peaks which are consistent with the emission peaks of H₂L,which depends on whether the energy of triplet state of H₂L and acac^-is matched with the lowest excited energy level of Ln ^III.2.OnelanthanidecomplexbridgedbyAcO^-wassynthesized,[Nd₄（acac）₃（L）₄（CH₃OH）₄（CH₃COO）]（5）.The four Nd^IIIII ions are bridged by twoμ₂-O oxygen atoms from AcO^-to form a Nd₄ cluster.X-ray diffraction data reveals that all the Nd^IIIII ions are nine-coordinated,but they adopt three kinds of coordination modes and show three types of configurations.The result of near-infrared luminescence property of complex 5 demonstrates that it just shows one Nd^IIIII characteristic emission peak at 1066nm.3.Five dinuclear lanthanide complexes have been synthesized successfully,[Yb₂（L）₂（acac）₂（CH₃OH）₂]·CH₃OH·H₂O（6）,[Lu₂（L）₂（acac）₂（CH₃OH）₂]·2CH₃OH（7）,[Er₂（L）₂（dbm）₂（CH₃OH）₂]·CH₃OH（8）,[Yb₂（L）₂（dbm）₂（CH₃OH）₂]·CH₃OH（9）,[Lu₂（L）₂（dbm）₂（C₂H₅OH）₂]（10）.Single-crystal X-ray analysis reveals that all the Ln^IIIII ions of complexes 6–10 are eight-coordinated and show distorted triangular dodecahedron geometry.The fluorescence properties of complexes 7 and 10 were also investigated and both of them exhibit several major emission peaks which are consistent with the emission peaks of H₂L in methanol solution.The results of near-infrared luminescence properties of complex 6 and 9 demonstrate that they can show one Yb^IIIcharacteristic emission peak.