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

Abstract

Five inorganic–organic hybrid compounds, namely, [Cu6Na2(Htrb)4(Mo6O19)(MoO4)6] (1), [Zn3(Htrb)(Mo10O34)]·8H2O (2), [Zn2(Htrb)(β-Mo8O26)(H2O)2]·6H2O (3), [Co2(Htrb)(β-Mo8O26)(H2O)2]·6H2O (4), and [Co2(Htrb)(γ-Mo8O26)(H2O)6]·8H2O (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 Cu6(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 Cu6(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 [β-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 [γ-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.