Four New Three-Dimensional Polyoxometalate-Based Metal-Organic Frameworks Constructed From [Mo6O18(O3AsPh)2]4- Polyoxoanions and Copper(I)-Organic Fragments: Syntheses, Structures, Electrochemistry, and Photocatalysis Properties

Four novel polyoxometalate-based copper(1)organic frameworks, namely, [Cu-2(I)(cis-L1)(2)][Cu-2(I)(trans-L1)(2)Mo6O18(O3AsPh)(2)] (1), [Cu-4(I)(L2)(4)Mo6O18(O3AsPh)(2)] (2), [Cu-4(I)(L3)(4)Mo6O18(O3AsPh)(2)] (3), and [Cu-4(I)(L4)(2)Mo6O18(O3AsPh)(2)] (4) (L1 = 1,3-bis(1,2,4-triazol-1-yl)propane, L2 = 1,4-bis(1,2,4-triazol-1-yl)butane, L3 = 1,5-bis(1,2,4-triazol-1-yl)pentane, and L4 = 1,6-bis(1,2,4-triazol-1-yl)hexane), have been successfully synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, infrared spectra (IR), UV-vis spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Compound 1 is composed of two crystallographically independent and distinct polymeric motifs: one-dimensional (1D) S-shaped chain and two-dimensional (2D) undulated layer. The S-shaped chains penetrated into the 2D parallel layers to generate an unusual 1D + 2D --> three-dimensional (3D) polypseudo-rotaxane framework. In 2, the As2Mo6 polyoxoanions in tetradentate modes link four neighboring -L2-Cu-L2- chains to produce a rare 3D trinodal (3,4)-connected self-penetrated framework with Point Symbol of (8(3))(2)(8(2)center dot 12(4)). In 3, adjacent Cu-I atoms are linked by As2Mo6 polyoxoanions and L3 ligands into a 2D layer. The layers are further interlocked by the two nearest neighboring ones to form a 3D polycatenated framework. In 4, L4 ligands bridge four Cu-I atoms to yield 2D wavelike layers, which are further linked by the octadentate As2Mo6 polyoxoanions to form a 3D tetranodal (3,4,6)-connected framework with Point Symbol of (6(3))(4.6(3).8(2))(6(4).8(2))(4(2).6(2).8(10).10). In addition, the photocatalytic activities of compounds 1, 3, and 4 for decomposition of methylene blue (MB) under UV light have been investigated. Moreover, their electrochemical properties have also been studied in 1 M H2SO4 aqueous solution.