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 CuI 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.