Design,Synthesis And Application Of Metal Organic Frameworks Based On Tetra-Carboxylic Ligands

The metal-organic frameworks(MOFs)are inorganic-organic hybrid materials with structural diversity,designability,and adjustability,which also generally have high porosity and specific surface area.Since the concept of MOFs was put forward,the research field of MOFs has experienced considerable development,and a large amount of MOFs with distinctive structural characteristics have been reported.MOFs have been widely used in gas adsorption and separation,catalysis,and substance detection.By adjusting the substituent groups in organic ligands,the structures and properties of the MOFs can be changed.Focusing on the in-depth exploration of the relationship between the structure and property differences brought by different substituent groups,it mainly carried out the following researches in this dissertation.(1)Compounds 1-3 were successfully prepared through the solvothermal reaction of In Cl₃ and three ligands with different substituent groups(H₄L-H,H₄L-OCH₃,and H₄L-NH₂).They were all anionic frameworks.However,different substituent groups caused them to have completely different frameworks and pore structures,which in turn leads to their different adsorption and separation capabilities for organic dyes and rare-earth ions.Both compounds 1 and 3 could adsorb cationic methylene blue(MB)with good capacity and a high rate.In particular,compound 1 exhibited great selectivity for cationic MB in the mixtures of MB and methyl orange(MO).However,the adsorption capacities of compounds 1 and 3 for rare-earth ions(Eu³⁺and Tb³⁺)were completely different.The adsorption capacity of 1 for Eu³⁺or Tb³⁺was equivalent.By adjusting the adsorption ratio of Eu³⁺and Tb³⁺,a series of white light materials could be obtained.The adsorption capacity of 3 for Eu³⁺was much higher than that for Tb³⁺,and therefore compound 3 could be used to purify and separate rare-earth ions.The different adsorption and separation capabilities of compounds 1 and 3 were caused by the difference in the ability of the host-guest interaction and the difference in pore sizes of the frameworks caused by the different substituent groups.(2)Compounds 4-6 were successfully prepared through the solvothermal reaction of Cu(NO₃)₂ and three ligands with different substituent groups(H₄L-H,H₄L-OCH₃,and H₄L-NH₂).They all had similar paddlewheel secondary building units[Cu₂(COO)₄].Among them,the structure formed by the ligand H₄L-H without special substituent groups was different from those formed by the ligands H₄L-OCH₃ and H₄L-NH₂ with special substituent groups.However,their stability was too poor to be further researched.After carefully studying the structures of compounds 4-6,compounds 7-9were obtained by directional introduction of nitrogen-containing ligands.The stability of compounds 7-9 was greatly improved,while they were maintaining the flexibility.The flexible frameworks of compounds 7 and 8 allowed them to undergo structural transformations in response to temperature and solvent changes,while the substituent group-OCH₃ would affect the response time of the structural transformations.(3)Compounds 10-17 were successfully prepared through the solvothermal reaction of Co(NO₃)₂,ligands H₄L-H,and different functionalized auxiliary N-based ligands.They all had similar pillar-layered structures,however,the different functionalized N-based ligands caused structural nuances.Compounds 10-17 had different CO₂ adsorption capacities caused by these structural nuances,such as the disordered ligands H₄L-H or not,the active sites for adsorption,the different sizes of the pores,the different polarities of the N-based ligands,the different host-guest interaction,etc.Significantly,compound 15 which contained pyridazinyl had the relatively highest CO₂ adsorption capacity among these compounds,which is 91.6cm³·g^-1(under the conditions of 273 K and 850 mm Hg).Compared with compound 10without special substituent groups,its adsorption capacity increased by 30.9%.(4)Compounds 18-20 were successfully prepared through the solvothermal reaction of Ni(NO₃)₂,4,4-bipyridine(BPY),and three ligands with different substituent groups(H₄L-H,H₄L-OCH₃,and H₄L-NH₂).Using the ligands H₄L-OCH₃ and H₄L-NH₂with special substituent groups could synthesize chiral MOFs through the substituent-inducing effect without adding any chiral inducers.However,the ligand H₄L-H without special substituent groups could only form the achiral MOFs.Substituent groups-NH₂had a stronger inducing effect than-OCH₃,which made the chiral information easier to transmit between the building units and less likely to be lost or changed.Therefore,compound 20 based on the ligand(L-NH₂)^4-could form the single chiral crystals,while compound 19 based on the ligand(L-OCH₃)^4-could only form the racemic twinning.Subsequently,the pre-synthesis method using the cheap chiral inducer D-camphoric acid was further designed to control the chiral growth direction of compound 20 and realized the controlled synthesis of a large quantity of single chiral compound 20-P4₁2₁2.