Research Of The Synthetic Method And Catalytic Capacities Of Solvent Template Induced MOFs

Metal-organic frameworks(MOFs) have emerged as a swift increasing research field in recent years, for their applications in hydrogen storage, magnetic materials, heterogeneous catalysis, drug delivery and sensor. The various applications should be attributed to their versatile topologies of MOFs and the ability to be purposedly controlled and adjusted. For example, MOFs generally need permanently porous structure and catalytically active sites to meet the demand as heterogeneous catalysts. Whereupon, an proper way to introduce metal sites and organic linkers that have catalytic activity and construct porous frameworks is of importance in synthesizing efficient MOF-based catalysts, and still needs further study.In this paper, by introducing different concentrations of solvent template(1,4-dioxane or THF) as structure-directing agent, the assemblies of 5,5’-(pentane-1,2-diyl)-bis(oxy)diisophthalic acid(H4pdpa) and transition metals(Zn2+ or Co2+) afford two series of complexes, namely, {[Zn2(pdpa)(H2O)2]·2H2O}n(1), {[Zn4(pdpa)2(H2O)8]·H2O}n(2), {[Zn5(pdpa)2(μ3-OH)2(H2O)3]·6H2O·CH3OH}n(3), {[Co2(pdpa)(CH3CN)(H2O)3]·CH3OH·H2O}n(4), {[Co2(pdpa)(CH3CN)(H2O)3]}n(5), and {[Co5(pdpa)2(μ3-OH)2(H2O)6]·2H2O}n(6). Interestingly, Zn-MOFs(1-3) have been synthesized under the same solvothermal conditions but only increasing the concentration of 1,4-dioxane, and they exhibit obviously structural conversions, from nonporous 1 to porous 2, and back to nonporous 3. This phenomenon is originated from the anion-π interactions between the oxygen atoms of 1,4-dioxane and the electron-deficient dicarboxylic acid aromatic rings of H4 pdpa, which could affect the configuration of the ligand and further controll the frameworks of 1-3. Similar template effect has been successfully observed in Co-MOFs(4-6). To further study the mechanism of this template effect, a systematic investigation has been taken to explore how different concentrations or kinds of structure-directing agents affected the structure of these MOFs.At last, the Zn/Co MOFs have been shown as available heterogeneous catalysts for tandem acylation-Nazarov cyclization reaction(for Zn-based MOFs) and the cascade cycloaddition reactions of aromatic nitriles with diamines(for Co-based MOFs), respectively. We summarized their catalytic activities and compared them to the structural features of these MOF-catalysts, by which the structure-activity relationship was clarified.