Solvent Templates Induced Porous Metal-Organic Materials: Conformational Isomerism and Catalytic Activity

Solvent templates induced Co-based metalorganic materials; conformational isomers {[Co-2(pdpa)(CH3CN)(H2O)(3)].CH3OH.H2O}(n) (<bold>1</bold>) and {[Co-2(pdpa)(CH3CN)(H2O)(3)]}(n) (<bold>2</bold>) and {[Co-5(pdpa)(2)(mu(3)-OH)(2)(H2O)(6)].2H(2)O}(n) (<bold>3</bold>) [H(4)pdpa = 5,5'-(pentane-1,2-diyl)-bis(oxy)diisophthalic acid] were synthesized under the same solvothermal conditions except with different concentrations of cyclic ethers (1,4-dioxane or tetrahydrofuran) as structure-directing agents. Structural transformations from a three-dimensional (3D) framework of <bold>1</bold> containing channels with dimensions of similar to 6 angstrom x 6 angstrom to a two-dimensional layer structure of <bold>2</bold> consisting of large open channels with a size of similar to 15 angstrom x 8 angstrom and then to a 3D nonporous framework of <bold>3</bold>, resulting from the different concentrations of cyclic ethers, were observed. The anion-pi interactions between electron-efficient oxygen atoms of cyclic ethers and electron-deficient dicarboxylic acid aromatic cores in H(4)pdpa imported into the synthetic process accounted for the conformational change of the ligand H(4)pdpa and the following structural variations. A systematic investigation was conducted to explore how different concentrations of structure-directing agents affected the frameworks of resultant metalorganic frameworks. Furthermore, <bold>1-</bold>3 were shown to be available heterogeneous catalysts for the synthesis of 2-imidazoline and 1,4,5,6-tetrahydropyrimidine derivatives by the cascade cycloaddition reactions of aromatic nitriles with diamines. The results showed that the catalytic activity of <bold>2</bold> was much higher than that of <bold>1</bold> and <bold>3</bold>, because of its unique structural features, including accessible catalytic sites and suitable channel size and shape. In addition, a plausible mechanism for these catalytic reactions was proposed, and the reactivitystructure relationship was further clarified.