Synthesis,Crystal Structure And Fluorescence Sensing Properties Of A Series Of Metal-Organic Frameworks Based On Aromatic Carboxylic Acids And Linear Polypyridine Ligands

Metal-Organic Frameworks（MOFs）have attracted much attention due to their advantages of structural design,easy modification and good stability.It has been widely used in catalysis,luminescence,gas adsorption and separation,drug transport,and sensing.MOFs have broad application prospects in the fields of ion recognition,temperature sensing,humidity sensing and small molecule recognition due to their diverse luminescence forms and the ability to change the luminescence effect of materials by adsorbing different guest molecules.MOFs with novel structure,high performance and multi-functionality can be constructed by using multi-carboxyl and nitrogen heterocyclic ligands with various coordination modes,which is of great significance.In this paper,aromatic carboxylic acids（thiophene dicarboxylic acid（H₂TDA）,Hemimellitic acid（H₃btc）,1,2,4-benzene tricarboxylic acid（H₃TLA）,2,6-naphthalenedicarboxylic acid（2,6–H₂NDC）,（carbonylbis（azanediyl））dibenzoic acid（H₂cbada）,（E）-4,4’-（ethene-1,2-diyl）dibenzoic acid（H₂SDC）,terephthalic acid（H₂TPA）,isophthalic acid（H₂IPA））were used as the main ingredients,and nitrogen heterocyclic ligands(4-amino-3,5-bis（4-pyridyl）-1,2,4-triazole（abpt）,1,3-di（pyridin-4-yl）urea（dpu）,1H-3,5-bis-（4-pyridyl）-1,2,4-triazole（bpt）,3-methyl-5-（pyridin-4-yl）-4H-1,2,4-triazol-4-amine（ampt）and 2,2’-（（（2-hydroxyphenyl）methylene）bis（5-amino-2,3-dihydro-1H-pyrazole-4,1-diyl））bis（ethan-1-ol）（hmadpe）were used as auxiliary ligands to react with a series of Zn（II）/Cd（II）and other metal salts to synthesize 26 unreported complexes.The main research results of this paper are as follows:1.Based on thiophene dicarboxylic acid and nitrogen heterocyclic ligands,nine complexes were synthesized by solvothermal method with transition metals such as Zn（II）and Cd（II）:[Zn₅（μ₃-OH）₂（TDA）₄（bpt）₂]_n（1）,{[Zn₃（TDA）₃（dpu）₃]·3DMF}_n（2）、{[Zn₅（μ₃-OH）₂（TDA）₄（abpt）₂]·CH₃OH·H₂O}_n（3）、[Cd₂（TDA）₂（bpt）₂]_n（4）、[Zn（TDA）（abpt）]_n（5）、[Co₅（μ₃-OH）₂（SO₄）₂（TDA）₂（bpt）₂（H₂O）₂]_n（6）、{[Co₂（TDA）₂（bpt）₂（H₂O）₂]·H₂O}_n（7）、[Zn₂（TDA）₂（bpt）]_n（8）、[Cd（TDA）（dpu）（DMF）]_n（9）.Among them,complexes（1）–（8）belong to the cylindrical 3D structure,and complex（9）belong to the 2D layered structure.Interestingly,complex（2）have a double-intercalation structure.The fluorescence sensing of complexes（1）and（2）were studied.The results showed that in solution,complex（1）has high selectivity and high sensitivity for Ag⁺,Cr₂O₇^2-and TNP（trinitrophenol）,complex（2）has high selectivity and high sensitivity for Fe³⁺,Ru³⁺,Cr₂O₇^2-,TNP and LVX（levofloxacin）,respectively.The possible sensing mechanism of complexes（1）and（2）to cations is attributed to the charge transfer from ligand to metal;the possible sensing mechanisms for Cr₂O₇^2-,TNP and LVX are attributed to effective energy resonance transfer or/and electron transfer.2.Eight unreported complexes with Zn（II）and Cd（II）have been synthesized by solvothermal method based on terephthalic acid,biphenyl tricarboxylic acid and heterocyclic ligands:{[Zn₃（TLA）₂（dpu）₂（H₂O）₂]·CH₃COCH₃}（10）,{[Zn₃（TLA）₂（dpu）₂（H₂O）₂]·CH₃COCH₃}_n（11）,{[Zn（btc）（dpu）]·0.5H₂O}_n（12）,{[Zn₃（btc）₂（bpt）₂（H₂O）₂]·8H₂O}_n（13）,[Cd₃（btc）₂（ampt）（H₂O）]_n（14）,{[Zn（Hbtc）（dpu）₂]·H₂O}_n（15）,{[Cd₄（Cl）₂（btc）₂（abpt）₃]·2H₂O}_n（16）,{[Ag₃（H₂btc）（Hbtc）（abpt）₂]·（H₂O）}_n（17）,and their crystal structures were elucidated.Among them,（10）-（13）,（16）-（17）are pillared 3D structures.Interestingly,complex（10）are 3-fold interpenetrated structures,（14）-（15）are 1D structures,and（15）are adjacent Zn（II）linked by btc^3-to form a’z’-shaped 1D chains.Complex（10）has high selectivity and sensitivity for TNP,LVX and L-Cys（L-cysteine）.Spectral studies have shown that there may be effective energy resonance transfer and/or photoinduced electron transfer between complex（10）and TNP;there is an effective fluorescence filtering effect between LVX and L-Cys.3.Nine unreported complexes with transition metals such as Zn（II）and Cd（II）were synthesized by solvothermal method based on aromatic diacids and nitrogen heterocyclic ligands:{[Zn₂（2,6-NDC）₂（dpu）]·2DMF}_n（18）,{[Zn₂（2,6-NDC）₂（dpu）]·1.5DMF}_n（19）,{[Zn₄（μ₄-O）（cbada）₂（dpu）₂]·2DMF}_n（20）,{[Zn（TPA）（dpu）]·DMF}_n（21）,{[Zn₂（SDC）₂（dpu）]·5DMF}_n（22）,{[Zn（SDC）（dpu）]·3DMF}_n（23）,[Zn（IPA）（dpu）]_n（24）,[Cd（OAc）₂（dpu）]_n（25）,{[Zn（TPA）（hmadpe）]·H₂O}_n（26）and their crystal structures were elucidated.Among them,（18）-（23）is 3D structure,（24）,（26）is 2D structure,（25）is 1D structure.Interestingly,complex（20）has large cavity,and the maximum cavity diameter is 22.8（?）.The fluorescence sensing properties of complexes（18）and（20）were investigated.Complex（18）with high selectivity and sensitivity for Ru³⁺,Cr₂O₇^2-,Mn O₄^-,TNP and LVX;complex（20）can identify Cu²⁺,Cr₂O₇^2-,TNP and LVX with high selectivity and sensitivity in solution.The spectra show that the fluorescence quenching mechanism of metal ions with complexes（18）and（20）may be attributed to the charge transfer from ligand to metal.There may be effective energy resonance transfer between Cr₂O₇^2-,Mn O₄^-and TNP;in addition,photoinduced electron transfer is also one of the reasons for TNP quenching complexes（18）and（20）;in addition,there may be effective fluorescence filtering effect between complexes（18）and（20）between LVX.