Syntheses,Structures And Properties Of Coordination Compounds Constructed From Carboxylic Acids And N-containing Heterocyclic Ligands

In this paper,our following synthetic strategy includes using organic carboxylic acid ligand as the main ligand and N-donor as the ancillary ligand reacting with metal ions based on the self-assembly under hydrothermal/solvothermal conditions.The crystal structure and other related properties of all compounds were analyzed.Coordination polymers with novel structure and excellent properties were obtained by adjusting the flexibility of organic carboxylic acid ligands,types of metal salts,solvents,reaction temperature and pH value to achieve self-assembly control of the structure,dimension,pore size and shape of coordination polymers.On the basis of the above work,the compounds were characterized by single-crystal X-ray diffraction,elemental analysis,FT-IR,UV-Vis spectroscopy,powder X-ray diffraction and thermogravimetric analyses.The fluorescence properties of coordination polymers were emphatically analyzed.The structural characteristics of coordination polymers and the selective response of coordination modes to nitrobenzene explosives were studied.At the same time,the mechanism of fluorescence quenching and dye adsorption of MOFs by the interaction between the small organic molecules and coordination polymers was investigated.The specific work is carried out as follows:1.Five new coordination polymers[Cd₂（oba）₂（phen）₂]_n（1）,[Mn₃（oba）₃（phen）₂]_n（2）,[Zn（oba）（phen）]_n（3）,[Mn（oba）（dmphen）]_n（4）and[Zn（oba）（dmphen）]_n（5）（H₂oba=4,4′-oxybis benzoic acid,phen=1,10-phenanthroline,dmphen=2,9-dimethyl-1,10-phen anthroline）have been synthesized by solvothermal method.The photoluminescent properties of compounds 1,3 and 5 in solid state were studied.Comound 2 are regarded as good candidates for adsorption of organic dyes,owing to their high surface area and tunable pore size.Four kinds of typical organic dyes with different sizes and charges were chosen as adsorption models.According to the change of color intensity and the determination result of ultraviolet visible spectrum,compound 2 exhibits high performance in the selective adsorption of Congo Red（CR）.The calculation results indicates that 2 can adsorb 64.4 mg.g^-1 of CR.This fast and high-capacity adsorption process is also very important for adsorbents in practical wastewater treatment.2.Three coordination polymers derived from the 3-（3’,5’-dicarboxylphen oxy）phthalic acid（H₄L）ligand have been constructed under solvothermal conditions with Zn（II）,Cd（II）ions,namely[Zn（H₂L）（2,2-bipy）]_n（6）,[Cd（H₂L）（phen）（H₂O）]_n（7）,[Cd（H₂L）（4,4-bipy）]_n（8）（2,2’-bipy=2,2’-bipyridine,phen=1,10-phenanthroline hydrate,4,4’-bipy=4,4’-bipyridine）.Compounds 6 and 7 are driven mainly by hydrogen bonding andπ???πstacking interactions to form 3D supramolecular networks,respectively.Compound 8 exhibits 2D layer network,and then shows2D→3D structure through C-H???O hydrogen bonds.The photoluminescent properties of compounds 6-8 in solid state has been investigated.Detailed property investigation shows that 6 could serve as the promising platform for luminescent sensing,which exhibits high selectivity and sensitivity toward Fe³⁺ions in the solution mixtures of metal ions and high detection for the trace content of 2,4-dinitrophenol with a high K_sv value of 1.83×10⁴ M^-1 and a low detection limit of 7.08×10^-44 mM.3.Five Ln-MOFs containing the uncoordinated-COOH based on3-（3’,5’-dicarboxyphenoxy）phthalic acid（H₄L）have been constructed under solvothermal conditions with Ln（III）ions,namely[Ln（HL）（H₂O）₂]_n（Ln=Eu（9）,Sm（10）,Gd（11）,Tb（12）,Tb（13））.The solid state fluorescence properties and structural characteristics of Ln-MOFs were studied.The pore channels of compound 9 contained uncoordinated-COOH and emitted the red fluorescence characteristic peaks of Eu³⁺.It was found that compound 9 could selectively response to Fe³⁺and CrO₄^2-ions in aqueous solutions with other ions co-existing by fluorescence quenching.The detection limits of compound9 on Fe³⁺and CrO₄^2-were 8.843×10^-3 mM and 4.552×10^-3 mM,respectively,indicating that compound 9 had extremely high sensitivity to detect Fe³⁺and CrO₄^2-.In addition,compound 9 showed a good linear correlation with fluorescence quenching when combined with a little acetone,so it can be used as a fluorescent sensor to efficiently response to acetone.