Isomeric organic ligand dominating polyoxometalate-based hybrid compounds: synthesis and as electrocatalysts and pH-sensitive probes

By introducing isomeric organic ligands into polyoxometalate (POM) systems, two new POM-based hybrid compounds, [Cu₆(m-pyttz)₂(H₂O)][HPMo₁₂O₄₀] (1) and [Ag₃(p-H₂pyttz)(p-Hpyttz)Cl][H₂PMo₁₂O₄₀]·6H₂O (2) (m-/p-H₂pyttz = 3-(pyrid-3/4-yl)-5(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), have been hydrothermally synthesized and characterized. Single-crystal structural analysis shows the m-pyttz ligands link Cu^I ions to generate a two-dimensional layer with hanger-like rhombus, which is pillared by the PMo₁₂ anions in 1. Compound 2 exhibits a three-dimensional supramolecular framework, in which PMo₁₂ anions are building blocks facilitating the extension of the whole structure. The influence of the coordination modes of m-/p-H₂pyttz on the structures is discussed in detail. Furthermore, electrochemical properties of 1 and 2 have been studied and they display excellent electrocatalytic activities toward the reduction of nitrite and hydrogen peroxide and pH-dependent electrochemical behaviors.