Synthesis,Structure And Properties Of Cd-MOFs Based On Phenyl-Imidazole Dicarboxylic Acids

Metal-organic framework complexes formed by cadmium ions(Cd-MOFs)have attracted much attention due to their diverse structures and easy functionalization.They have potential application value in many directions such as adsorption and separation,catalysis and sensing.In view of the lack of in-depth researches on the pore structure of Cd-MOFs in the literatures,the thesis selected three different phenyl-imidazole dicarboxylic acid ligands to construct new Cd-MOFs and studied the pore structure and control methods.Further explored the properties of the solid-state fluorescence and Cd-MOFs heterogeneous explosives molecular recognition properties for applications ideas.It reads as follows:1.Phenyl-imidazole dicarboxylic acid(H3PhIDC)ligand,p-methoxyphenyl-imidazole dicarboxylic acid(p-H3MOPhIDC)ligand,m-methoxyphenyl-imidazole dicarboxylic acid(m-H3MOPhIDC)ligand and monodentate auxiliary ligand like pyridine(Py),benzimidazole(Biz),bidentate ligand 4.4'-Bipyridine(4.4'-Bpy)were chosen to construct 9 new Cd-MOFs through hydrothermal and solvothermal methods.Through structural characterization,the molecular formulas were determined:[Cd4(HPhIDC)4(C2H5OH)(H2O)]n(1),[Cd4(HPhIDC)4(CH3CN)(H2O)]n(2),[Cd(p-HMOPhIDC)(C2H5OH)]n(3),[Cd2(p-HMOPhIDC)2(H2O)2·DMF]n(4),[Cd2(p-HMOPhIDC)2(NH3)(H2O)]n(5),[Cd2(p-HMOPhIDC)2(Py)(C2H5OH)]n(6),[Cd8(p-HMOPhIDC)8(Biz)]n(7),{Na2[Cd2(p-MOPhIDC)2(4.4'-Bpy]}n(8)and[Cd4(m-HMOPhIDC)4(4.4'-Bpy)4]}n(9).Structural analysis shows that the nine Cd-MOFs present four different pore structure units:Channel ? is a quadrilateral channel containing six Cd²⁺ions(MOF 1 and 2),and Channel ? is a double channel containing ten Cd²⁺ions quadrilaterals staggered.(MOF 3-7),Channel ? is a rectangular channel(MOF 8)containing eight Cd²⁺,and the Channel ? is a dual channel(MOF 9)with eight Cd²⁺ions in a staggered arrangement.Channels ? and ? are constructed by the ligand H3PhIDC,p-H3MOPhIDC and monodentate auxiliary ligands,respectively.Channel ? uses the bidentate bridging ligand4.4'-Bpy instead of the monodentate ligand of ?.M-H3MOPhIDC replaces p-H3MOPhIDC of ? in Channel ?.Among the MOFs,the bridging modes of phenyl-imidazole dicarboxylic acid ligands are?₃ and?₄(I),?₃(?),?₄(?)and?₂(?),respectively.By the above analysis,the structure and size of the pores of the Cd-MOFs are mainly affected by ligand-linking bridge modes.2.The solid-state fluorescence properties shows that the peaks of the nine Cd-MOFs have different degrees of displacement compared with the corresponding ligands.In terms of strength change,MOF 1 showed partial quenching,Cd²⁺heavy atom effect was the main reason.MOF 3-8 showed different degrees of enhancement,which was attributed to the fact that after ligand coordination,the molecular skeleton was fixed to reduce the energy loss of thermal vibration.MOF 9 showed complete quenching,which may be related to its pore structure.3.MOF 6 and 8 showed good fluorescence recognition performance for 2,4-dinitrotoluene(DNP)and 2,4,6-trinitrophenol(TNP).Under the same concentration of explosives,the quenching rates of MOF 6 for DNP and TNP were 94%and 97%,respectively.The quenching rates of MOF 8 for DNP and TNP were 98%and 99%,respectively.The quenching rates of other explosives were lower than 20%.The change of fluorescence intensity in the range of 4.98×10^-6?1.94×10^-4M has a good linear relationship with the concentration of DNP and TNP.MOF 6 and 8 could be reused more than four times.The above results indicate that MOF 6 and 8 can be used for quantitative detection of DNP and TNP.