Synthesis And Gases Adsorption Properties Of Metal-Organic Frameworks Based Upon N-heterocyclic Carboxylates

In recent years,Metal-Organic Frameworks(MOFs)have attracted great attentions from chemists and materials scientists,because of their unique topologies and potential applications in gas storage and separation,optics,magnetics,chemical sensor,catalysis and biomedicine.With the development of the research,people begin to pay more attention to design MOFs to make the structure conform to the expectation and have excellent properties.On the basis of abundant research,scientists have summarized some effective synthetic strategies.In the early 1990s,Robson initially introduced the "node and spacer" approach.Later on,O'Keeffe and Yaghi proposed the '"secondary building units" approach.Under the guidance of these strategies,numerous MOFs have been synthesized and reported.In this article,we have synthesized four V-shaped ligands.Under the guidance of secondary building units,we used cupric paddle-wheel clusters to construct four MOFs.Through structural characterization and gas adsorption test of these MOFs,we can study the structure-activity relationship.Hence,the influence of different modified groups on gas adsorption can be investigated,which may provide some reference for the design and synthesis of MOFs materials with high separation efficiency and excellent storage performance.Firstly,we design V-shaped pyridyl-tetracarboxylic ligands by inserting triazolyl groups.Compound 1 were synthesized by assembly with cupric paddle-wheel clusters.And Compound 1 is(3,36)-connected MOFs,its surface area and pore volume are 2166 m2 g-1 and 0.98 cm3 g-1.Moderate surface area and large framework density make the Compound 1 behave well in methane storage.The value at 35 bar surpass the older DOE's target and achieve 86%of the new DOE's target.The working capacity at 65 bar is 168 cm3/cm3(STP).Secondly,we design V-shaped tetracarboxylic ligands by inserting tetrazoles group.Compound 2 were synthesized by assembly with cupric paddle-wheel clusters.And Compound 2 is(4,4)-connected MOFs,its surface area and pore volume are 1988 m2 g-1 and 0.86 cm3 g-1.The nitrogen atoms in the tetrazoles group do not coordinate,but are exposed to the pore in the form of Lewis base.Thus,the adsorption capacity of carbon dioxide was greatly improved,and the value at 273 K and 1 bar reached 208 cm3 g-1(29 wt%).This value is greatly improved compared with the prototype skeleton or amino modified skeleton compound.In addition,we got two V-shaped pyridyl-dicarboxylic ligands by extending the ligand in a novel way.Compound 3 and 4 is(3,6)-connected rtl-MOFs with high porosity.However,the gas adsorption results have not been satisfied after many attempts.So we chose the supercritical carbon dioxide extraction technique to activate the MOFs.Even so,the BET surface area of compound 4 is only 400 m2 g-1,which is far away from the theoretical value.Although we have not obtained the pore data of these two compound,this method still has some guiding significance for the construction of MOFs with high porosity.