Syntheses, Structures And Electro-optical Properties Of Coordination Polymers Based On Flexible Multi-carboxylate Ligand

As a new type of porous solid material, metal-organic frameworks(MOFs) have attracted many researchers’ attention because of their diversified structures and unique structure–property relationship. Particularly, the MOFs based on flexible aromatic carboxylate ligands are appealing because they could possesse versatile structures and have excellent performance in applications. which benefit their good potentials to gas separation, storage, magnetic, luminescent, electrical materials, etc. Recently, scientists’ attention on proton conducting materials is on the rise because of the inceasing requirement for energy. The proton conducting material is one of the most critical compoment in the fuel cell. Metal-organic frameworks compounds are found to be new candidaes for proton conducting materials because of its unique designed molecular structure and the tailored tunnel walls. In addition, the rare earth metal ions coordination polymers have strong luminescence, it gradually shows the attractive practical prospect in fluorescent probe combined with the advantages of the metal-organic framework materials with porous structures.In this thesis, our work mainly includes the following two parts:1. A flexible aromatic carboxylic acid ligand H4 L [H4L = 5-(3, 5-dicarboxybenzyloxy) isophthalic acid)] was synthesized. Then we got two different compounds [Cd3(L)2(DMAc)2(H2O)2]n(1),[Cd2(L)(H2O)3]n(2) with the ligand H4 L and cadmium nitrate by solvothermal method. The X-ray single crystal diffraction analyses reveal that the compound 1 crystallizes in the triclinic space group Pī, three Cd atoms linked by oxygen atoms of carboxy groups forms a trinucleaer Cd-O cluster, the clusters are linked by ligands each other to form a 2D plane, which generate a 3D supermolecular through hydrogen-bond. The compound 2 crystallizes in the monoclinic chrial space group P21, two Cd atoms linked by oxygen atom of carboxy group forms a binucleaer Cd-O cluster, the clusters are linked by ligands each other to form a 3D network. This result indicates that the different solvent have influenced the forming of coordination polymer, in this proceeding the flexible ligand twist itself to acclimatize the different environment. The fluorescence test shows that the fluorescence indisity of compound 1 and 2 is stronger than the ligand and the slight red-shift had taken place.2. A series of homeomorphism rare earth coordination polymers{[Ln2(L)2]·(H2O)3·(Me2NH2)2}n(Ln = La(3), Ce(4), Pr(5), Nd(6), Sm(7), Eu(8), Gd(9), Tb(10), Ho(11), Er(12)) are obtained by solvothermal method based on this flexible aromatic carboxylic acid ligands and different rare earth nitrates. Due to the unique properties of strong luminescence of Eu complexes and the super water stability and host-guest structure of this series structure of rare earth coordination polymer, we choose the compound 8(Eu-MOF) for sensing of metal ion and the result reveal that the Eu-MOF could selectively sense the Cu2+ and Fe3+ with naked eyes through the fluorescence quench. To further understand the process of cation exchange and the quenching mechanism, we performed time-dependent luminescence intensity, PXRD patterns, IR spectra, and elemental analysis(EA) and ICP-MS of the solid sample Fe3+/Cu2+@Eu-MOF as well as their filtrate after ‘‘ion-exchange’’. Combined with these above experimental results, we proposed that the luminescence quenching for Fe3+@Eu-MOF is attributed to the collapse of the original crystal structure and the loss of Eu3+. On the contrary, Cu2+ ions exchanged with [(CH3)2NH2]+ might interact with the carboxylate on the backbone in Cu2+@Eu-MOF, which reduces the energy transfer efficiency from ligands to Eu3+ ions, thus leading to the quenching effect. In addition, the dimethylammonium cations as the rich proton source present the same chiral distribution reside in the second larger helical channel and the largest helical channels are occupied by the rare helical water chain that form a hydrogen-bond network, which provide a potential proton pathway. So we evaluate its proton conduction and herein Eu-MOF is proved to be an excellent proton conducting material with high proton conductivity(1.1×10-3 S cm-1) at low relative humidity(68% RH).