Microporous Metal-Organic Frameworks: Structures, in Situ Formation of Ligand, and Crystal-to-Crystal Transformations

Among these new microporous metal-organic frameworks (MOFs) {[Cu-17(I)(L1)(12)X-2]X-3(H2O)(n)}(infinity) (1, X = Cl, 1a, n = 6; 1b, 1c, n = 5, 1d, n = 3; 2,X = Br, 2a, n = 5; 2b, n = 3; L1 = 3,5-bis(4-aminophenyl)-1,2,4-triazolate), 1a and 2a were obtained through in situ copper-mediated ring conversion of 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole into L1 under hydrothermal conditions, while the others were generated through interesting single-crystal-to-single-crystal transformations with an accompanying color change from red to black. In the process of synthesis, when Cu-II salt was used as starting reactant, the Cu-I complex la was obtained; so the redox reaction clearly took place under this condition. The fascinating features of these structures are the double-stranded helical chains and the largest metallamacrocycle based on triazolate ever reported. These isomorphous complexes adopt the rare binodal six-connected networks. In the solid state at low temperature (similar to 273 K), the red crystal sample 1b displays an emission band at similar to 585 nm upon photoexcitation at 467 nm.