Design,Synthesis And Properties Of Sulfonic Acid Based Metal-Organic Frameworks

Metal-organic frameworks（MOFs）are coordination polymers formed by the self-assembly of metal or metal clusters and organic ligands through coordination bonds.Because of its high porosity,high surface area,easy modification and other advantages,it is widely used in gas storage,separation,catalysis,sensing and other fields.Among them,sulfonic acid is an organic framework material,because of the strong acidity and high electronegativity of-SO₃H,it is easy to form hydrogen bond grid with adjacent free water molecules and coordination water molecules,so that the functional groups of sulfonic acid groups have great advantages in proton conduction and other aspects.Based on this,the following aspects of metallic organic framework materials containing sulfonic acid groups were studied in this paper:By regulating small organic molecules containing sulfonic acid as guest molecules,we obtained two novel MOFs containing sulfonic acid Cu₂PZA₄1,6-NDS（Compound 1,PZA=pyrazine,1,6-NDS=1,6-naphthalene disulfonate）and CuPZA_1.51,5-NDS_0.5（compound 2,PZA=pyrazine,1,5-NDS=1,5-naphthalene disulfonate）.The framework of these two compounds is composed of Cu（I）and pyrazine connection.We change the hydrogen bond network density of the two MOFs materials by changing the sulfonic acid group position of the guest molecule,and thus improve the proton conductivity.This study shows that the proper design of organic guest small molecules containing sulfonic acid groups can effectively regulate the proton conductivity of MOFs.In order to further improve the proton conductivity of MOFs,we introduced two organic guest small molecule strategies to obtain a MOF material CuPZA₂2,7-NDS containing two organic guest small molecules of sulfonic acid group（compound 3,PZA=pyrazine,2,7-NDS=2,7-naphthodisulfonate Acid）.Two small organic molecules,2,7-naphthalene disulfonic acid and pyrazine,were selected and introduced into one-dimensional Cupric MOFs pore as guest molecules.Due to the strongπ…πinteraction between naphthalene ring and pyrazine,pyrazine and 2,7-naphthalene disulfonate are stacked in parallel to maintain the stability of the MOF pore,and abundant hydrogen bond grids are obtained through hydrogen bonding between sulfonic acid groups and water molecules in one-dimensional chains.We investigated the intrinsic proton conductivity of the material,and found that the material showed a wide temperature range of proton conductivity suitable for working in sub-zero environment,among which the proton conductivity at 323 K reached 9.27×10^-3S·cm^-1,better than most MOFs materials.Then,by using different lanthanide metal salts and sulfonic acid organic ligands,two novel bimetallic lanthanide clusters of MOFs,EuMOF and SmMOF,were obtained.The two MOFs form a helical one-dimensional chain structure through the bimetallic sodium lanthanide cluster,and form a 3D structure through the connection of two carboxylic acid groups on 5-sulfonic acid m-phthalic acid,in which the uncoordinated sulfonic acid group is exposed in the pores of MOFs,and can be used as proton carriers.Since the porosity of EuMOF is greater than that of SmMOF,the number of free water molecules and DMA molecules in the pores is increased（DMA=N,N-dimethylacetamide）,more free solvent molecules and sulfonic acid groups form more favorable channels for proton transmission,resulting in higher proton conductivity of EuMOF.In addition,the fluorescence sensing performance of EuMOF was tested,and it was found that EuMOF had sensitive detection ability for Fe³⁺ions.