Construction And Property Studies Of Metal-organic Frameworks Assembled By Nitrogen Heterocyclic Carboxylate

Metal-Organic Frameworks,also named as MOFs,are constructed withdiverse metallic ions and various organic ligands.For the flexible tunability and designability of the above two part,MOFs who armoured with multiple functional sites are highlighted in an extended field such as gas storage and separation,heterogeneous catalysis,fluorescent sensing,drug loading and sustained release and pollutant adsorption and degradation.Since the first outcome of MOFs,discovering the relationship between structures and properties,further designing ordered structures to some targeted applications are the soul of MOFs development.N-heterocyclic carboxylic ligand,as one of the bifunctional ligand,is superproforming in directing assembly of MOFs structure and its inner active sites.On the one hand,N and O site of the ligand can induce a metallic ion to construct different secondary building units,and on the other,different metallic ions can be induced to coordinate with different binding sites to construct heterometal-organic frameworks.Furthermore,some metallic may only coordinate with one kind of binding sites and remain the other as exposed active sites.For the advantages above,we choose pyridinic carboxylic acid and azolic carboxylic acid as two kinds of N-heterocyclic carboxylic ligands to study its impact on building MOFs and its inner functional sites with various metallic ions of different coordinating peculiarities.First,wechoosedpyridiniccarboxylicligand,L¹=5-?5-Carboxy-pyridin-3-yl?-isophthalic acid,and p-block element–indium constructed compound 1-3.In there frameworks,N-coordinated monomeric indium ions and O-coordinated trimeric indium clusters are coexistence,which is rare in reported literatures.Through adding different halide ions into synthetic system,we harvested compound 1-3 modified with coordinated Cl,Br and I ions.In the experiment of catalyzing CO₂ with epoxides into cyclic carbonates,three compounds revealed highly and good ordered efficiencies,which is of great values for the synthesis of catalysts with multiple active sites and studing the order for various sites.Second,we choosed Cu and In as metallic sources to study their differences in constructingMOFswithpydriniccarboxylaticligand–L²=5-?3-Carboxy-phenyl?-nicotinic acid and L³=2-?5-carboxypyridin-2-yl?terephthalic acid.Three Cu based MOFs with same metallic source and ligand but different structures were maded.In their frameworks,both N and O of the ligand are coordinated.While in the structure of two indium based MOFs–compound 7 and 8,which were assembled by L² and L³,respectively,only carboxylic O are coordinated.The exposed pydrinic N were as Lewis base site in frameworks for functionalization of fluorescent sensing,organic dyes removal and cycloaddition of CO₂ with epoxides.Third,we altered the organic ligand to azolic carboxylic acid,L⁴=2,2'-methylenebis?1H-imidazole-4,5-dicarboxylicacid?andL⁵=3,5-bis?4'-carboxy-phenyl?-1,2,4-triazole,and constructed Zn based MOFs–compound 9,Co based MOFs–compound10 and In based MOFs–compound11.Similarly,in the transition metal based MOFs,N and O site are co-coordinated,while in the p-block element indium organic frameworks,only O atom coordinated with metal center.Carboxylate-O and azolic-N existed in compound9?10 and 11,respectively,which provide possibilities for CO₂ chemical fixation.In summary,we studied the performance of pydrinic carboxylic acid and azolic carboxylic acid in“bifunctional ligand directing strategy”and concluded the features of structures and properties of the assembled MOFs.