Five Keggin-based compounds modified by bis- and mono-[1,3,4]triazole ligands: characterization, and selective photocatalytic and electrochemical properties

Abstract

By adjusting three different bis- and mono-[1,3,4]triazole ligands, five Keggin-based compounds modified by Cu and triazole derivatives were hydrothermally synthesized, [Cu(BBYT)_2.5(HPMo₁₂O₄₀)]·2H₂O (1), [Cu(BBYT)_2.5(HPW₁₂O₄₀)]·3H₂O (2), [Cu₃(OH)Cl(BBYT)₃(SiW₁₂O₄₀)]·2H₂O (3), [Cu(Tybz)₂(HPMo₁₂O₄₀)]·H₂O (4) and [Cu₄(Tbz)₄(OH)₆(H₂SiW₁₂O₄₀)] (5) (BBYT = 1,4-bis(1,3,4-triazole-1-methyl)benzene, Tybz = 4-[1,3,4]triazol-4-ylmethyl-benzylamine, Tbz = 4-benzyl-4H-[1,3,4]triazole). Compounds 1 and 2 are isostructural, showing a two-dimensional (2D) grid-like metal–organic network. The Keggin anions provide O atoms to connect the two adjacent 2D metal–organic networks, constructing a three-dimensional (3D) framework. In compound 3, all four N atoms of BBYT connect Cu atoms to form a one-dimensional (1D) chain, assisted by hydroxyl groups. Some BBYT in this chain extend the structure to a 3D framework with Keggin anions in the structural gap. Instead of the bis(triazole) ligands in 1–3, compounds 4 and 5 use mono(triazole) ligands Tybz and Tbz to construct Keggin structures. Compound 4 includes mono-nuclear clusters [Cu(Tybz)₂]²⁺, which are linked by Keggin anions to form a 2D structure. Compound 5 has a 1D copper chain with Tbz ligands fused by Cu atoms. Tbz molecules alternate up and down the chain. The Keggin anions are connected to the chain alternately above and below. The 1-, 2- and 3-CPEs exhibit excellent multifunctional electrocatalytic activities. Compounds 1–3 show selective photocatalytic activity for the degradation of methylene blue under ultraviolet irradiation.