Synthesis And Properties Of MOFs And HOFs Based On Tetrakis(4-carboxyphenyl) Ethylene Ligands

Porous frame materials are the hottest research area in recent years and have become one of the most challenging topics in the fields of chemistry,physics,and nanoscience.It contains metal-organic frameworks(MOFs),covalent organic frameworks(COFs)and Hydrogen-Bonded Organic Frameworks(HOFs).They are considered to have potentially important applications due to their high specific surface area,adjustable pore size,low density,and diverse structural functions.Metal-organic framework compounds possess a variety of skeletal structures and have potential applications in gas separation and storage,catalysis,sensing,and molecular magnetism.Hydrogen bonded organic framework materials,like traditional molecular sieves and porous carbon materials,have shown good application prospects in proton conduction,fluorescent probes and drug molecule delivery.MOFs and HOFs materials with specific physical and chemical properties can be purposefully assembled by rational selection of metal centers and organic ligands,donors and acceptors,and reaction conditions.The aromatic carboxylic acid organic ligands have various coordination modes,hydrogen bonding interactions and supramolecular interactions such as ????? stacking.And it is a class of multifunctional organic ligands and donors widely used in MOFs and HOFs materials.Based on this,tetrakis(4-carboxyphenyl)ethylene(H4TCPE)organic compounds was used as organic ligands for MOFs and donor materials for HOFs.Four kinds of MOFs materials coordinated with rare earth elements(Eu,Gd,Tb,Dy)and four kinds of HOFs materials under different reaction conditions were synthesized,and characterized and studied their structures and properties.The main contents include the following points:(1)Study on properties of tricarboxy-coordinated rare earth-based MOFs.Based on carboxy-coordinated rare earth MOFs,four kinds of three-dimensional MOFs containing rare earth element(Eu,Gd,Tb,Dy)coordination were synthesized,and only three carboxylic acids were involved in the coordination by adjusting the acid concentration in the synthesis reaction.The physical and chemical properties of the framework material itself can be altered by exchanging hydrogen ions on the free carboxylic acid with lithium ions.By measuring the p H values before and after the exchange,it was found that the p H values before and after the exchange were significantly changed.After detection by ICP,it is found that some hydrogenions are indeed exchanged by lithium ions.In later studies,it was found that MOFs before and after exchange have significant properties changes in gas adsorption and proton conduction.It is shown that the rare earth-based MOFs have good application prospects in gas selective adsorption and conduction.(2)Synthesis and properties of HOFs with different hydrogen bonding strengths.H4 TCPE was used as the donor,and zigzag bipyridines(4,4-bipy,azpy,bpa,bpe)were used as acceptors to synthesize four different hydrogen bond strengths and different morphology HOFs crystal materials under volatile and solvothermal methods.The aromatic carboxylic acid compound and the nitrogen atom on the pyridine ring easily form hydrogen bonds,and are connected end to end to form a crystalline HOFs material having a three-dimensional structure.The HOFs synthesized under the volatilization method are extremely unstable at high temperature and solvent,and are easy to collapse and dissolve.Therefore,other HOFs materials were synthesized by solvothermal method compared to the volatilization method,the HOFs synthesized by the solvothermal method have significantly improved thermal stability and stability in solvents.The main reason can be attributed to the increase in the shortening of the hydrogen bond distance and hydrogen bond energy.Then we performed fluorescence recognition and gas adsorption experiments on HOFs formed under solvothermal conditions.It is found that this kind of material has good fluorescence recognition effect on Fe3+(turn-off)and Al3+(turn-on).The above indicates that this kind of HOFs material has a very promising application prospect on fluorescent probes and drug carriers.