Design,Synthesis And Properties Of Zirconium-based Metal-Organic Frameworks

Metal-organic Frameworks（MOFs）,as a class of structurally highly ordered crystalline porous materials,have always been the focus of research in materials science because of ultra-high specific surface area,low density and controllable adjustment of the framework structure.In metal-organic framework materials,Zr-MOFs exhibit far more stability than other MOFs due to the high coordination mode between the secondary structural units（SBUs）and ligands in the structure.Zr-MOFs with ultra-high stability have demonstrated wide application potential in gas adsorption separation,heterogeneous catalytic reaction,drug delivery,degradation of toxic substances and chemical sensors.Designing organic ligands with specific functions to construct Zr-MOFs structures can achieve specific applications.In this paper,eight highly conjugated carboxylic acid ligands were designed and synthesized,and a series of Zr-MOFs were constructed by combining high-valent metal Zr.The specific research content is as follows:（1）Three bidentate carboxylic acid ligands as 4,4’-（（1E,1’E）-1,4-phenylenebis（ethylene-2,1-Diradical））Dibenzoic acid（L1）,4,4’-（（1E,1’E）-naphthalene-1,4-diylbis（ethylene-2,1-diyl））dibenzoicacid（L2）,4,4’-（（1E,1’E）anthracene-9,10-diylbis（ethylene-2,1-diyl））dibenzoic acid（L3）were successfully synthesized.And nuclear magnetic resonance spectroscopy and X-ray single crystal diffraction analysis were used to confirm the structure.Two microporous Zr-based and Hf-based metal organic frameworks MOF-1 and MOF-2 were synthesized by solvothermal reaction of ligand L3 with metal salts ZlCl₄ and HfCl₄,respectively.And the X-ray single crystal diffraction,powder diffraction analysis,thermogravimetric analysis,scanning electron microscopy,N₂ adsorption at77K,CO₂ adsorption at 298K,infrared spectra,UV spectra and fluorescence spectra were used to characterize the structure.X-ray single crystal diffraction analysis shows that MOF-1 and MOF-2 are isomorphous highly symmetric cubic systems with a space group of Fd-3m and a network topology of fcu-c.MOF-1 exhibits excellent thermal stability,chemical stability,high N₂ adsorption of 1470 m²/g and CO₂ adsorption of 43 cm³/g.In addition,MOF-1 also exhibits a pronounced solvatochromic behavior that can show macroscopic color changes in different solvents.The special nature of lyotropic discoloration makes MOF-1 as a chemical sensor for rapid detection of solvent molecules.（2）Tetradentate carboxylic acid ligand 1,2,4,5-tetrakis（（1E）-2’-（4’’-benzoic acid）vinyl）]benzene（L4）,tridentate carboxylic acid ligands 4,4’,4’’-（（1E,1’E,1’’E）-benzene-1,3,5-trisyltris（ethylene-2,1-Diradical））tribenzoic acid（L5）,tridentate carboxylic acid ligands 4,4’,4"-（（1E,1’E,1’’E）-Triphenylbenzene-1,3,5-trisyltris（ethylene-2,1-diyl））tribenzoic acid（L6）,hexadentatecarboxylicacidligand4,4’,4’’,4’’’,4’’’’,4’’’’’-（（1E,1’E,1’’E,1’’’E,1’’’’E,1’’’’’E）-benzene-1,2,3,4,5,6-hexahydrohexyl（ethylene-2,1-diyl））hexabenzoic acid（L7）and 4,4’,4’’-（（1E,1’E,1’’E）-（（（benzene-1,3,5-tricarbonyl）tris（azanediyl））tris（benzene-4,1-diyl））tris（diazene-2,1-diyl））tribenzoic acid（L8）were successfully designed and synthesized.The structure were determined by ¹H NMR and ¹³C-NMR.A highly porous Zr-based metal organic framework was constructed by using solvothermal reaction of ligand L4 and metal salt ZlCl₄.And the x-ray single crystal diffraction,powder diffraction analysis,thermogravimetric analysis,scanning electron microscopy,N₂ adsorption at 77K,CO₂ adsorption at298K,infrared spectra,UV spectra,and fluorescence spectra were used to characterize the structure.X-ray single crystal diffraction analysis showed that the MOF-4 crystals was a highly symmetrical cubic system with space group Pm-3m for ftw-a topology.In addition,MOF-4 exhibits excellent thermal stability,1050 m²/g N₂ adsorption and 27 cm³/g CO₂ adsorption.