Five polyoxometalate-based inorganic-organic hybrid compounds constructed by a multidentate N-donor ligand: syntheses, structures, electrochemistry, and photocatalysis properties

Five inorganic-organic hybrid compounds, namely, [Cu6Na2(Htrb)(4)(Mo6O19)(MoO4)(6)] (1), [Zn-3(Htrb)(Mo10O34)]center dot 8H(2)O (2), [Zn-2(Htrb)(beta-Mo8O26)(H2O)(2)]center dot 6H(2)O (3), [Co-2(Htrb)(beta-Mo8O26)(H2O)(2)]center dot 6H(2)O (4), and [Co-2(Htrb)(gamma-Mo8O26)(H2O)(6)]center dot 8H(2)O (5), have been synthesized under hydrothermal conditions, where Htrb = hexakis(1,2,4-triazol-ylmethy1) benzene. Their structures have been determined by single-crystal X-ray diffraction analyses and characterized by infrared spectra (IR), elemental analyses and powder X-ray diffraction (PXRD) patterns. In compound 1, eight Htrb ligands bridge six Cu(II) atoms to form a metal-organic Cu-6(Htrb)(8) cage. Neighboring cages are further linked by the arms of the Htrb ligands to generate a fascinating 3D framework. Interestingly, each inorganic [Mo6O19](2-) anion was incorporated into the Cu-6(Htrb)(8) cage. In 2, adjacent [Mo10O34](8-) anions are linked by the bridging oxygen atoms to form 1D inorganic molybdenum oxide chains, which are extended by Zn(II) atoms into a 2D layer. Adjacent layers are further linked by the Htrb ligands in hexadentate modes to yield a 3D framework. Compounds 3 and 4 are isostructural, where the [beta-Mo8O26](4-) anions are bridged by the metal atoms to yield an infinite chain. The chains are further joined together by the Htrb ligands to form a 3D (4,5,6)-connected net. In compound 5, the Co(II) atoms are bridged by the Htrb ligands to generate 1D chains, which are further extended through the Mo-N bond between the Htrb ligands and the [gamma-Mo8O26](4-) anions into a 3D (3,4,6)-connected net. Moreover, the optical band gaps, photoluminescence, electrochemistry and the photocatalytic properties for methylene blue (MB) degradation of 1-5 have also been investigated.