MOF Materials Based On N And O Ligands

MOF materials（as known as porous coordination polymers）are self-assembled from metal ions（or metal ion clusters）and organic ligands through coordination bonds.Therefore,it means that MOF materials are composed of an inorganic structural unit and an organic structural unit.Just as different with traditional porous materials such as zeolite and activated carbon,MOF materials have the characteristics of large specific surface area and large porosity.Furthermore,ideal MOF materials can be constructed through target design.As a research object in the intersection of coordination chemistry and material chemistry,MOF materials are becoming more and more well-known.Their specific structures show unique properties,and their application prospects are quite wide,including but not being limited to chemical probes,supercapacitors,catalysis,etc.As a branch of its application,the storage and separation of gases have attracted widespread attention from scientific researchers in recent years.In this dissertation,two types of N and O-containing ligands were designed and synthesized,including hybrid isophthalic acid（H₂L1,H₂L2,and H₂L3）and pyridine-N,and its oxide-functionalized polycarboxylic acid（H₃L1,H₄L1,H₄L2,H₄L3,and H₄L4）,and then their corresponding copper and cobalt-based metal organic framework compounds were solvothermally constructed.Firstly,the structure and gas adsorption performance of cobalt（II）-based metal organic framework compounds were regulated by changing the solvothermal reaction conditions;and then the application values of target framework compounds in natural gas purification,one-step ethylene purification and acetylene capture were explored.Finally,the effects of positional isomerization and N-oxidation functionalization on selective gas adsorption performance were investigated.Details were listed as follows:1.Structural regulation of MOFs:With 5-（3-aminopyridin-4-yl）isophthalic acid（H₂L1）as a ligand,two Co（II）-based structures were constructed by controlling the reaction variables,that is,only changing the identity of inorganic acid under the other same solvothermal conditions.The novel Co（II）-based MOFs are termed ZJNU-16 and ZJNU-17.Single-crystal X-ray diffraction studies and analyses showed that both ZJNU-16 and ZJNU-17 are three-dimensional networks,but they display different inorganic SBUs,organic ligand conformations and network topologies.ZJNU-16 is an anionic network composed of discrete trinuclear Co₃-based clusters as inorganic SBUs,while ZJNU-17 is an electrically neutral network featuring a nanotubular helical Co-carboxylate chains as an inorganic SBU,thus representing a rare nanotubular helical chain-based MOF.Gas adsorption studies have found that ZJNU-16 has almost no adsorption,while ZJNU-17 can preferentially adsorb C₂H₂ over CO₂and CH₄,indicating its potential for C₂H₂ separation and purification.This work revealed that the structural regulation of MOFs by changing the inorganic acid is an effective method for synthesizing MOFs with diverse structures.2.Functional exploration of MOFs:Natural gas purification,C₂H₄purification and C₂H₂ capturation are three important but very challenging separation processes in the chemical industry.Three N and O-containing ligands were designed and synthesized,and their copper（II）-based MOFs（ZJNU-15,ZJNU-7 and ZJNU-14）were constructed by solvothermal reactions,and their structural characterizations and gas adsorption studies were carried out.ZJNU-15 is a three-dimensional network,which is composed of5-（3-aminopyridin-5-yl）isophthalic acid as the ligand and tetranuclear copper cluster Cu₄O（COO）₆（Py-N）₃（H₂O）as the inorganic SBU.This inorganic SBU has never been reported in the literature.This MOF not only has good water stability,but also display the potential to separate and purify natural gas and C₂H₂.ZJNU-7 is a three-dimensional network constructed with5-（pyrimidin-5-yl）isophthalic acid as the ligand.The cage surface of ZJNU-7 is enriched with electronegative chloride ions,so it can preferentially adsorb C₂H₂and C₂H₆ from a C₂ hydrocarbon mixture at the same time,and thus can be used for one-step adsorption-phase purification of C₂H₄.ZJNU-14 is a three-dimensional network constructed by a N-oxide functionalized tricarboxylate.There is a dense C₂H₂ molecular binding environment in the framework,which can capture trace amounts of C₂H₂ molecules from C₂H₄ and recover C₂H₂ from CO₂ and CH₄,indicating its potential for the purification of C₂H₄ and the recovery of C₂H₂.3.Research on the structure-property relationship of MOFs:A series of bis（isophthalic acid）ligands were designed and synthesized through the strategies of positional isomerization and N-oxide functionalization,and then Nb O-type copper（II）-based MOFs（ZJNU-1,ZJNU-2,ZJNU-3 and ZJNU-4）were constructed.Afterwards,the structural characterization and gas adsorption of them were studied.The results showed that positional isomerization can modulate the gas adsorption performance of MOFs,while N-oxide functionalization can significantly boost the gas adsorption performance.Particularly,gas adsorption studies have found that the adsorption capacity and selectivity of the N-oxide functionalized MOFs ZJNU-3 and ZJNU-4 are much better than those of the non-oxidized MOFs ZJNU-1 and ZJNU-2.Among them,the C₂H₂/CH₄ adsorption selectivity of ZJNU-3 and ZJNU-4 was increased by25.7%and 45.4%,respectively.It shows that N-oxide functionalization MOFs not only have excellent uptake capacity of C₂H₂,but also have excellent adsorption selectivity towards C₂H₂,which overcomes the trade-off problem associated with uptake capacity and adsorption selectivity.This work revealed that the positional isomerization and the N-oxide functionalization are effective methods to synthesize MOFs with improved performance.