Four New Three-Dimensional Polyoxometalate-Based Metal–Organic Frameworks Constructed From [Mo<sub>6</sub>O<sub>18</sub>(O<sub>3</sub>AsPh)<sub>2</sub>]<sup>4–</sup> Polyoxoanions and Copper(I)-Organic Fragments: Syntheses, Structures, Electrochemistry, and Photocatalysis Properties

Four novel polyoxometalate-based copper­(I)-organic frameworks, namely, [Cu<sup>I</sup><sub>2</sub>(<i>cis</i>-L1)<sub>2</sub>]­[Cu<sup>I</sup><sub>2</sub>(<i>trans</i>-L1)<sub>2</sub>Mo<sub>6</sub>O<sub>18</sub>(O<sub>3</sub>AsPh)<sub>2</sub>] (<b>1</b>), [Cu<sup>I</sup><sub>4</sub>(L2)<sub>4</sub>Mo<sub>6</sub>O<sub>18</sub>(O<sub>3</sub>AsPh)<sub>2</sub>] (<b>2</b>), [Cu<sup>I</sup><sub>4</sub>(L3)<sub>4</sub>Mo<sub>6</sub>O<sub>18</sub>(O<sub>3</sub>AsPh)<sub>2</sub>] (<b>3</b>), and [Cu<sup>I</sup><sub>4</sub>(L4)<sub>2</sub>Mo<sub>6</sub>O<sub>18</sub>(O<sub>3</sub>AsPh)<sub>2</sub>] (<b>4</b>) (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 <b>1</b> 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) poly<i>pseudo</i>-rotaxane framework. In <b>2</b>, the As<sub>2</sub>Mo<sub>6</sub> 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<sup>3</sup>)<sub>2</sub>(8<sup>2</sup>·12<sup>4</sup>). In <b>3</b>, adjacent Cu<sup>I</sup> atoms are linked by As<sub>2</sub>Mo<sub>6</sub> 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 <b>4</b>, L4 ligands bridge four Cu<sup>I</sup> atoms to yield 2D wavelike layers, which are further linked by the octadentate As<sub>2</sub>Mo<sub>6</sub> polyoxoanions to form a 3D tetranodal (3,4,6)-connected framework with Point Symbol of (6<sup>3</sup>)­(4·6<sup>3</sup>·8<sup>2</sup>)­(6<sup>4</sup>·8<sup>2</sup>)­(4<sup>2</sup>·6<sup>2</sup>·8<sup>10</sup>·10). In addition, the photocatalytic activities of compounds <b>1</b>, <b>3</b>, and <b>4</b> for decomposition of methylene blue (<b>MB</b>) under UV light have been investigated. Moreover, their electrochemical properties have also been studied in 1 M H<sub>2</sub>SO<sub>4</sub> aqueous solution.