| Metal-Organic Frameworks(MOFs)are constructed by forming coordination bonds between metal units(or secondary structural units)and organic ligands.MOFs have shown great application value in the fields of sensing,electrochemistry,catalysis,and energy storage due to their rich topological structure,large specific surface area,high porosity and tunable chemical composition,and at present,it has developed into one of the research directions of many chemical branches.In addition,it is worth noting that the choice of organic ligands plays a crucial role in the construction of MOFs,because the structure,size,coordination sites and coordination modes of organic ligands are directly related to the structure of MOFs.As a class of functional organic ligands,N-heterocyclic carboxylic acid ligands possess promising research prospects.This is because such ligands involve multidentate coordination sites(N,O),which retain strong chelating ability with metal ions,and can coordinate with metal ions through coordination bonds to form a structurally stable framework.Second,the carboxyl oxygen atoms in the ligands can be fully or partially deprotonated to form structures of different dimensions.At the same time,it can also be used as a proton donor or acceptor to form a hydrogen bond network with guest molecules(water molecules,etc.).In addition,the uncoordinated nitrogen atoms in the ligands can adjust the pore size and pore polarity,thereby obtaining porous materials with unique structures and properties.In this paper,based on the ligands 1-(4-Carboxyphenyl)-3-(pyridin-4-yl)-pyrazole and 5-(3-carboxyphenyl)picolinic acid,a variety of novel MOFs have been designed and synthesized,and series of characterizations were carried out,including single crystal X-ray diffraction,powder X-ray diffraction,elemental analysis and infrared spectroscopy.The luminescent properties of luminescent MOFs in terms of fluorescence were also investigated.The research content is mainly divided into the following two parts:1.Five isostructural 2D layered MOFs:[M(cppp)2]n[M=Co(1),Ni(2),Cu(3),Zn(4)and Cd(5)]and one 1D chain MOF:[Cd(cppp)Cl(H2O)]n(6)were successfully synthesized under hydro(solvo)thermal conditions by use 4-(3-(pyridin-4-yl)-1H-pyrazol-1-yl)benzoic acid(Hcppp)as an organic ligand.Their structures were resolved and basic characterization was performed,including single crystal X-ray diffraction,powder X-ray diffraction,elemental analysis,and infrared spectroscopy.The electrochemical properties of MOF-2 were tested.The results show that in the three-electrode system,MOF-2 exhibits high specific capacitance and long-term stability.In addition,the fluorescence properties of MOF-4 and MOF-5 were also tested.Fluorescence sensing experiments show that MOF-4 and MOF-5 express good luminescence properties and can detect nitrobenzene(NB)and dichloromethane(CH2Cl2)in aqueous solution.After the addition of NB,MOF-4 and MOF-5 exhibited obvious fluorescence quenching,the corresponding quenching coefficients were 5.53×10~3M-1and2.38×10~3M-1,respectively,and the detection limits were 6.38×10-6M and 6.13×10-6M,respectively.Cycling experiments for 5 cycles demonstrated the good reproducibility of MOF-4 and MOF-5.However,after the addition of CH2Cl2,MOF-4 and MOF-5 exhibited significant fluorescence enhancement,with enhancement coefficients of 3.70×10~3M-1and2.27×10~3M-1,respectively,the corresponding detection limits are 7.75×10-6M and 5.80×10-6M,respectively.2.Using 5-(3-carboxyphenyl)picolinic acid(H2cppca)as the organic ligand,four new Ln-MOFs:[Eu(cppca)(OH)]n(7),[Gd(cppca)(OH)(H2O)]n(8),[Dy(cppca)(OH)]n(9),[Nd O(cppca)]n(10)were synthesized under solvothermal conditions with a series of rare earth metals.Its structure was solved,and a series of basic characterizations were followed including single crystal X-ray diffraction,powder X-ray diffraction,elemental analysis and infrared spectroscopy.Fluorescence experiments confirmed that MOF-7 can effectively sense various organic amines,including aniline,dimethylamine,diethylamine,trimethylamine,triethylamine,ethylamine,ethylenediamine,n-propylamine.The calculated KSVis 1.14×10~4M-1,1.10×10~4M-1,8.67×10~3M-1,7.48×10~3M-1,9.72×10~3M-1,8.87×10~3M-1,6.66×10~3M-1,7.57×10~3M-1in order,and the corresponding detection limits are 3.01×10-6M,4.01×10-6M,3.02×10-6M,3.28×10-6M,3.00×10-6M,3.38×10-6M,3.05×10-6M,3.16×10-6M. |
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