Assembly of Three Ni^II–Bis(triazole) Complexes by Exerting the Linkage and Template Roles of Keggin Anions

Three inorganic–organic hybrid compounds based on Keggin-type polyoxometalate (POM) and Ni^II-bis(triazole) complexes, namely, [Ni₂(L¹)₄(SiW₁₂O₄₀)]·H₂O (1), [Ni₂(H₂O)₄(L²)₄(HL²)₂][PMo₁₂O₄₀]₂·2H₂O (2), and [Ni₃(L¹)₅][PMo₁₂O₄₀]₂·14H₂O (3) (L¹ = 1,4-bis(1,2,4-triazol-1-yl)butane, L² = 1,6-bis(1,2,4-triazol-1-yl)hexane), have been obtained under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction analyses, elemental analyses, IR spectra, and thermogravimetric (TG) analyses. Compound 1 exhibits a (6⁶) three-dimensional (3D) Ni-L¹ framework with hexagonal channels, in which [SiW₁₂O₄₀]^4– anions have been accommodated as tetradentate linkages. In compound 2, the Ni-L² motif exhibits a 3D supramolecular network templated by [PMo₁₂O₄₀]^3– (PMo₁₂) anions. In compound 3, the Ni-L¹ motif is a two-dimensional (2D) layer, which is linked by PMo₁₂^a anions to construct a 3D framework. The 3D frameworks interpenetrate with each other to form a 2-fold interpenetrating structure, which exhibits two kinds of channels. The other discrete PMo₁₂^b anions, acting as inorganic templates, are embedded in the larger channels. The Keggin anions in 3 exert not only linkage but also template roles. In addition, electrochemical properties of 1-bulk modified carbon paste electrode (1–CPE) and 3–CPE have been studied in 1 M H₂SO₄ aqueous solution.