Inorganic-organic hybrid compounds based on octamolybdates and metal-organic fragments with flexible multidentate ligand: syntheses, structures and characterization

Six polyoxometalate-based (POM) hybrid materials based on octamolybdate building blocks and metal-organic fragments with flexible multidentate ligand, namely [Cu-2(II)(ttb)(2)(beta-Mo8O26)(H2O)(2)]center dot 2H(2)O (1), Cu-4(I)(ttb)(2)(beta-Mo8O26)(H2O) (2), [Cu-4(I)(ttb)(3)(beta-Mo8O26)] (3), [Ni-2(ttb)(2)(beta-Mo8O26)(H2O)(6)]center dot 2H(2)O (4), [Zn-2(ttb)(2)(alpha-Mo8O26)(H2O)(2)] (5), and [Ag-4(ttb)(2)(beta-Mo8O26)] (6), where ttb = 1,3,5-tris(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethyl benzene, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, TGA, IR spectra, and electrochemistry. Compounds 1 and 2 exhibit three-dimensional (3D) 2-fold interpenetrating frameworks with (3,6)-connected (4(1)center dot 6(2))(4(2)center dot 6(10)center dot 10(3)) and (3,4)-connected (6(2)center dot 8(1))(2)(6(2)center dot 8(4)) topologies, respectively. We are not aware of any other examples of interpenetrating (3,6)- and (3,4)-connected frameworks which involves the octamolybdates. Compound 3 shows a rare two-dimensional (2D) 2-fold interpenetrating network structure. In compound 4, a 3D supramolecular framework with the channels is constructed by the hydrogen-bonding interactions between (beta-Mo8O26)(4-) polyanions and the Ni-ttb double layers, in which the guest (beta-Mo8O26)(4-) anions are included. If Zn center dot center dot center dot O interactions are considered, the structure of 5 is a 3D (3,4)-connected framework with (4 center dot 8(2))(4 center dot 8(2)center dot 10(3)) topology. In 6, the ttb ligand as a tetradentate ligand links the Ag atoms to yield a 2D POM-based network. By careful inspection of the structures of 1-6, it can be seen that the ttb ligand, the metal ion and the coordination mode of the octamolybdate anion play important roles in the formation of the POM-based MOFs.