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

摘要

Six polyoxometalate-based (POM) hybrid materials based on octamolybdate building blocks and metal-organic fragments with flexible multidentate ligand, namely [Cu~(II)_2(ttb)_2(β-Mo_8O _(26))(H_2O)_2]·2H_2O (1), Cu ~I_4(ttb)_2(β-Mo_8O _(26))(H_2O) (2), [Cu~I_4(ttb) _3(β-Mo_8O_(26))] (3), [Ni_2(ttb) _2(β-Mo_8O_(26))(H_2O) _6]·2H_2O (4), [Zn_2(ttb) _2(α-Mo_8O_(26))(H_2O)_2] (5), and [Ag_4(ttb)_2(β-Mo_8O_(26))] (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 (4~1·6~2)(4 ~2·6~(10)·10~3) and (3, 4)-connected (6~2·8~1)2(6~2·8 ~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 (β-Mo_8O_(26))~(4-) polyanions and the Ni-ttb double layers, in which the guest (β-Mo_8O_(26)) ~(4-) anions are included. If Zn?O interactions are considered, the structure of 5 is a 3D (3, 4)-connected framework with (4·8 ~2)(4·8~2·10~3) 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.