A series of metal-organic loops templated by [SiMo12O40]4- and [β-Mo8O26]4- anions by using double chelate ligands: amperometric sensoring and selective photocatalytic properties

By using the double chelating ligands 2,3-di-pyridin-2-yl-pyrazine (L1) and 2,3-di-pyridin-2-yl-quinoxaline (L2), six new polyoxometalate-based compounds, namely [AgI4(L1)4(SiMo12O40)] (1), [CuII6(L1)6(H2O)6(SiMo12O40)3]·6H2O (2), [CuII(L1)(H2O)(β-Mo8O26)0.5] (3), [AgI2(L2)(β-Mo8O26)0.5] (4), [CuII(L2)(β-Mo8O26)0.5] (5) and [ZnII(L2)(β-Mo8O26)0.5] (6), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis, IR spectra and elemental analyses. Using the double chelating ligand L1, compounds 1–3 were obtained. In compound 1, there is a tetra-nuclear Ag loop with four Ag atoms linked by four L1 ligands. The [SiMo12O40]4− anions are sandwiched by these loops alternately. Compound 2 has a hexa-nuclear shield-like Cu cluster, in which six Cu atoms are connected by six L1 ligands. The channel formed by the packing hexa-nuclear loops accommodates the [SiMo12O40]4− anions. By using [β-Mo8O26]4− instead of [SiMo12O40]4−, compound 3 was obtained containing a zigzag metal–organic chain. The chains are linked by [β-Mo8O26]4− anions to construct a layer. By changing L1 to L2, compounds 4–6 containing metal–organic loops were built. In compound 4, two L2 ligands are linked by two Ag atoms to form a bi-nuclear loop. The [β-Mo8O26]4− anions as tetra-dentate inorganic subunits link bi-nuclear loops to build a 2D layer. Compounds 5 and 6 are isostructural, with bi-nuclear Cu/Zn–L2 loops connected by [β-Mo8O26]4− anions alternately to construct a 1D chain. In addition, we also studied the electrochemical properties and selective photocatalytic properties of compounds 1–6.