Subtly tuning one N site of benzyl-1H-triazole ligands to build mono-nuclear subunits and tri-nuclear clusters to modify polyoxometalates

Abstract

By using two kinds of organic ligands (1-benzyl-1H-(1,2,4)triazole (2-btz) and 1-benzyl-1H-(1,3,4)triazole (3-btz)), six polyoxometalate (POM)-based compounds were hydrothermally synthesized and structurally characterized, [Ag₄(2-btz)₄(HPMo₂^VMo₁₀^VIO₄₀)] (1), [Ag₄(2-btz)₄(SiW₁₂O₄₀)] (2), [Ag₄(2-btz)₅K(SiW^VW₁₁^VIO₄₀)]·13H₂O (3), [Cu₄(2-btz)₁₆(Mo₈O₂₆)₂] (4), [Cu₃(3-btz)₈(H₂O)₄](PMo₁₂O₄₀)₂·4H₂O (5) and [Cu₇(3-btz)₁₆(OH)₂(H₂O)₄(P₂W₁₈O₆₂)₂]·16H₂O (6). Compounds 1 and 2 are isostructural with two sets of Ag–(2-btz) chains linked by Keggin anions to construct a “ladder”. Adjacent “ladders” are further connected by Ag1–O13 bonds to build a 3D framework. In compound 3, the anion dimers are linked by Ag5–O9 bonds to form a 1D chain. The chains are fused by Ag3 and K ions and a 3D framework of 3 is built. In compound 4, the Mo₈ anions are linked by [Cu(2-btz)₄]²⁺ subunits to construct a 3D structure. By changing 2-btz to 3-btz, we obtained a linear tri-nuclear cluster [Cu₃(3-btz)₈(H₂O)₄]⁶⁺ in compound 5. The discrete PMo₁₂ anions combine with tri-nuclear clusters through hydrogen bonding interactions to construct a 2D supramolecular layer. Compound 6 contains a cycle tri-nuclear cluster-supporting anion [Cu₃(3-btz)₆(OH)(H₂O)₂(P₂W₁₈O₆₂)]⁻, which is further connected by one [Cu(3-btz)₄]²⁺ subunit to construct a discrete anion dimer. The title compounds show good electrocatalytic activities for reducing nitrite, hydrogen peroxide and bromate. These compounds also exhibit excellent photocatalytic activities for the degradation of methylene blue (MB, 1–6 as catalysts) and Rhodamine B (RhB, 5 and 6 as catalysts). Additionally, the magnetic properties of compounds 5 and 6 have been investigated.