Synthesis And Properties Of Metal-Organic Framework Materials Based On 3-substituted Imidazo[1,2-a]Pyridine Ligand

The research content of this thesis is based on the preliminary work of our laboratory and is based on MOFs materials.Firstly,a new 3-position substituted imidazo[1,2-a]pyridine ligand,namely,5-(2-chloroimidazo[1,2-a]pyridine-3-carboxamido)isophthalic acid(H2L)was synthesized and characterized by 1H-NMR spectroscopy.Based on this ligand,three isostructural one-dimensional coordination polymers,[ML(H2O)2]n(M=Zn(1),Ni(2)and Co(3))were synthesized under the solvothermal conditions,and structurally characterized by single crystal X-ray diffraction,infrared spectroscopy,powder X-ray diffraction and elemental analyses.The coordination polymer 1 reveals similar photoluminescent spectrum to H2L ligand,but possesses the enhanced phosphorescent emission and higher phosphorescent quantum yield,compared to H2L ligand.Furthermore,the magnetic properties of coordination polymers 2 and 3 have been investigated,the results show there are antiferromagnetic interactions between the Ni? ions or Co? ions in 2 or 3.This work opens up new possibilities to construct new coordination polymers or metal-organic frameworks by using 3-position substituted imidazo[1,2-a]pyridine derivatives as ligand.The reasons for generation of one-dimensional structures are that the coordination points of metal ions were occupied by water molecules,and/or the non-coordination of N in the ligand also leads to the generation of low-dimensional structures.So we changed the reaction conditions and a novel flexible metal-organic frameworks(MOFs),[ZnL]·H2O·DMA(USTC-1),with interesting topology has been constructed based on H2L.This MOFs was characterized by IR spectroscopy,thermogravimetry,single-crystal,and powder X-ray diffraction methods.The single crystal analysis reveals four carboxylate groups connect two zinc ions to generate a paddlewheel secondary building unit(SBU).Each paddlewheel SBU is six-connected to six L2-ligands,and each L2-is three-connected to three SBUs,thus,the framework can be described as a binodal(3,6)-connected three-dimensional(3D)flexible network.The low N2 and CO2 gas uptake should be attributed to the flexible vibration of amide chains at ligands that close the pore window,however,the closed pore window can be opened by dye molecules,such as Rhodamine B(RB),Methyl Orange(MO)or Methylene Blue(MB).Two methods for dye encapsulation were investigated:soaking and in situ encapsulation.PXRD data showed that the framework in USTC-1 was unchanged after encapsulation of dyes.Interestingly,RB@USTC-1 simultaneously displayed the characteristic emissions of both the RB dye and the MOFs,resulting in red/blue two-color luminescence with intensity ratio of 4.5 and tunable phosphorescence color.Moreover,RB@USTC-1 and MO@USTC-1 could undergo protonation upon exposure to HCl vapor,and reveal reversible phosphorescent color switching in the response to acid-base vapor stimuli.The present work provides a promising approach for synthesizing novel flexible MOFs and a new access to develop the phosphorescent and stimuli-responsive MOFs materials via encapsulation of various guests.