The Construction And Properties Of Metal-Organic Frameworks Based On N-Containing Carboxylic Ligands

In the past few decades,metal-organic frameworks（MOFs）as crystalline materials,have attracted increasing attention due to their special and diverse porous structures and functional performances.They have shown fascinating applications in various fields such as gas storage and separation,heterogeneous catalysis,sensors,drug delivery and so forth.The components of secondary building units（SBUs）of metal nodes and organic linkers in MOFs exhibits flexible tunability and modification,allowing for the special structure and performance of MOFs to be designed and synthesized.However,there are still some barriers that currently hinder the real world application of these MOFs-based materials in the areas mentioned above.For example,many of the current MOFs suffer from poor stability.The construction of MOFs with specific functional sites is still facing great challenges.Therefore,giving full play to the unique advantages of MOFs in structural modulation to design and synthesize stable MOFs with special functional sites is still problem to be solved.To resolve the above two issues,the existing work focuses on introducing azoles into the MOFs skeleton by means of nitrogen heterocyclic carboxylic acid ligand modulation,which can not only improve the stability of its skeleton,but also give rich functional characteristics.Through the corresponding structure and property characterization,the influence of specific sites in the structure of MOFs on the relevant functional properties can be analyzed and summarized.The corresponding research contents are summarized as follows:（1）Two distinct self-interpenetrating MOFs,[Cu₂（L1）₂]（1,L1=4-（bis（4-benzoic）amino）-4H-1,2,4-triazole）and[Cu₂（L2）₂]（2,L2=4,4’-（1H-1,2,4-triazol-1-ylmethylene）bis-benzoic acid）,have been constructed based on two similar di-carboxylic acid containing triazole unit and Cu（Ⅱ）ions under solvothermal environments.Their structural analysis indicate that two MOFs are highly porous structure with 3,6T18 and Flu topological networks.Compounds 1 and 2 keep good stability in a certain concentration of acidic and alkaline aqueous solutions.In addition,gas sorption studies and theoretical calculations reveal their different porous structure.The results would provide help for the construction of MOFs with high porosity and stability.（2）Three MOFs with diversity of secondary structural units,[（NH2Me2）][Zn3（L3）（bentz）]（3）,[（NH₂Me₂）₂][Zn_6.5（L3）_1.5（tz）₆（H₂O）₆]（4）and[（NH₂Me₂）₆][Zn₉（L3）₃（H₂O）₂（ade）₂（μ-O）₂]（5）,（bentz=benzotriazole,Htz=1H-1,2,3-triazole,ade=adenine）,have been synthesized by using porphyrin tetracarboxylic acid ligand with Zn（Ⅱ）ions in the presence of different azoles-containing as auxiliary ligands under solvothermal environments.Compounds 3-5 are anionic frameworks and exhibit the distinct selective adsorption capacity toward various cationic dyes.Among them,compound 5 has the fastest adsorption rate.It is worth noting that the pore surface of compound 5 exposes the open Watson-Crick site,which may serve as a potential action site to enhance the interaction with guest molecules.（3）A water-stable Tb-MOF,[Tb₄（L1）₆（H₂O）₈]（6,L1=4-（bis（4-benzoic）amino）-4H-1,2,4-triazole）,has been constructed by using triazole dicarboxylic acid ligands and Tb（Ⅲ）ions.By anchoring the triazole empty coordination group onto the skeleton of Tb-MOF,not only the water stability of the material is improved,but also the luminescent sensing properties to a variety of substrates could be efficiently enhanced.Compound 6 can be used for the detection of metal cations,anions and organic small molecules.In addition,it shows high selectivity and sensitivity to detect trace nitro explosives in water and gas phase.（4）By utilizing the V-shaped di-carboxylic acid containing triazole unit and Zr（IV）ions,a new Zr-MOF,[Zr₆O₄（OH）₈（H₂O）₄（L4）₄]_n（7,L4=4,4’-（4-Amino-4H-1,2,4-triazole-3,5-diyl）dibenzoic acid）,has been fabricated.Compound 7 has both rigid framework and flexible coordination environment,exhibiting high chemical stability.It can adsorb and fix different Ni cluster units（seven core and three core nickel clusters）in solution to obtain new compounds 8 and 9.More importantly,the definite configuration could be detected via the normal SCXRD technology to realize the crystallographic visualization of postsynthetic metal clusters for the first time.In addition,the catalytic properties show that the trinuclear nickel clusters in compound 9 have more open metal sites and ordered structures,which greatly enhance the catalytic activity of ethylene dimerization.