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

<p>By introducing isomeric organic ligands into polyoxometalate (POM) systems, two new POM-based hybrid compounds, [Cu₆(<i>m</i>-pyttz)₂(H₂O)][HPMo₁₂O₄₀] (<b>1</b>) and [Ag₃(<i>p</i>-H₂pyttz)(<i>p</i>-Hpyttz)Cl][H₂PMo₁₂O₄₀]·6H₂O (<b>2</b>) (<i>m</i>-/<i>p</i>-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 <i>m</i>-pyttz ligands link Cu^I ions to generate a two-dimensional layer with hanger-like rhombus, which is pillared by the PMo₁₂ anions in <b>1</b>. Compound <b>2</b> 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 <i>m</i>-/<i>p</i>-H₂pyttz on the structures is discussed in detail. Furthermore, electrochemical properties of <b>1</b> and <b>2</b> have been studied and they display excellent electrocatalytic activities toward the reduction of nitrite and hydrogen peroxide and pH-dependent electrochemical behaviors.