Synthesis And Luminescence Sensing Properties Of Metal-Organic Frameworks Based On Acetylenic Bond Conjugated Carboxylic Acid

Metal-organic frameworks（MOFs）are inorganic-organic hybrid materials with intramolecular pores or channels formed by self-assembly of metal ions or clusters and organic ligands through coordination bonds.By choosing organic ligands with different structures,or changing the synthesis strategy,the structure and size of MOFs pores can be adjusted,so that MOFs can be more widely used in gas storage,adsorption and separation,drug release,catalysis,optics,magnetism,etc.When using metal ions with characteristic emission to construct MOFs or introducing organic ligands with much conjugated systems into the MOFs structure,luminescent MOFs can be synthesized.The method of applying luminescent MOFs-based sensors to fluorescence recognition has a fast response speed,high sensitivity,good selectivity,and low detection limit.In this paper,two conjugated carboxylic acid ligands containing acetylenic bonds were selected,and seventeen MOFs materials were synthesized by solvothermal method.The single crystal structure was analyzed by X-ray single crystal diffraction,and further characterized by powder X-ray diffraction,thermogravimetric,infrared and elemental analysis.The solid-state fluorescence properties of the complexes were studied,and some of the complexes were used as fluorescent probes to sense metal ions,anions,nitroaromatic explosives,and antibiotics.The detailed work of this paper is as following:1.Using 3-amino-4,4’-ethynyl dibenzoic acid（H₂L1）as the ligand,four MOFs were synthesized by solvothermal method with Eu³⁺,Sm³⁺,Gd³⁺,and Zn²⁺:[Eu（L1）_1.5（H₂O）₂]_n（1）,[Sm（L1）_1.5（H₂O）₂]_n（2）,[Gd（L1）_1.5（H₂O）₂]_n（3）,[Zn₄O（L1）₃]_n（4）.X-ray single crystal diffraction shows that the secondary building units for complexes 1-3 are[RE₂（CO₂）₄];connecting completely deprotonated L1^2-form a three-dimensional network frame structure.Complex 4,centered on the[Zn₄O]⁶⁺metal cluster,is connected to the carboxyl group of the deprotonated carboxyl group L1^2-to form a secondary building unit Zn₄O（CO₂）₆,which is connected to a cubic pore through the ligand L1^2-,and further connected into a three-dimensional framework,the obtained complexes were tested for solid-state fluorescence,and complex 1 was used as a fluorescent probe to identify metal ions,anions,and nitro aromatic explosions.In the application of chemical compounds,it is found that complex 1can selectively recognize Cu²⁺,Cr₂O₇^2-,TNP.2.3-amino-4,4’-ethynyl dibenzoic acid（H₂L1）with Tb³⁺,Eu³⁺,Sm³⁺,Gd³⁺,Er³⁺,Ho³⁺,Y³⁺,Yb³⁺and 2-fluorobenzoic acid acts as a structure directing agent and modulator,eight MOFs were synthesized by solvothermal method:[Tb₆（μ₃-OH）₈（L1）₆]_n（5）,[Eu₆（μ₃-OH）₈（L1）₆]_n（6）,[Gd₆（μ₃-OH）₈（L1）₆]_n（7）,[Er₆（μ₃-OH）₈（L1）₆]_n（8）,[Sm₆（μ₃-OH）₈（L1）₆]_n（9）,[Ho₆（μ₃-OH）₈（L1）₆]_n（10）,[Y₆（μ₃-OH）₈（L1）₆]_n（11）,[Yb₆（μ₃-OH）₈（L1）₆]_n（12）.The single crystal structure analysis shows that the complexes 5-12 are isomorphic,and the rare earth metal ions are connected to L1^2-through the hexanuclear secondary building units[RE₆（μ₃-OH）₈（CO₂）₁₂]to form a regular tetrahedral cage.Two regular tetrahedral cages further form a regular octahedral cage,and the three-dimensional frame formed by orderly infinite extension can be simplified to the topology of fcu.The solid-state fluorescence of complexes5 and 6 showed characteristic emission peaks of Tb³⁺and Eu³⁺,respectively,and the sensing performance of complex 5 as a fluorescent probe was further studied.It was found that complex 5 has a good recognition performance for Ni²⁺,Cr₂O₇^2-,TNP,nitrofurantoin（NFZ）,nitrofurantoin（NFT）,and furazolidone（FZD）.3.Using 5-[（4-carboxy-2-aminophenyl）ethynyl]isophthalic acid（H₃L2）as the ligand,five MOFs were synthesized by solvothermal method with Eu³⁺,Tb³⁺,Sm³⁺,Gd³⁺,and Dy³⁺:[Eu（L2）（DMF）₂]_n（13）,[Tb（L2）（DMF）₂]_n（14）,[Sm（L2）（DMF）₂]_n（15）,[Dy（L2）（DMF）₂]_n（16）,[Gd（L2）（DMF）₂]_n（17）.The single crystal structure analysis shows that the complexes13-17 are isomorphic,and the two adjacent binuclear secondary building units RE₂（CO₂）₄are connected to form a chain through the same carboxyl group on the ligand,and further through the two ligands.The terminal carboxyl group obliquely penetrates into a three-dimensional frame,and there are two one-dimensional channels of different sizes along the crystallographic c axis direction.The solid-state fluorescence spectrum of complex 13 shows the characteristic peak of Eu³⁺.Through studying the fluorescence recognition performance,it is found that complex 13 can selectively recognize Fe³⁺,Cr₂O₇^2-,TNP.