Assembly Chemistry Of Keggin Polyoxometalates Decorated By Mixed-Valence Multinuclear Copper-Organonitrogen

Metal–organic frameworks （MOFs） have been paid intensive attention in recentyearsbecause of their applications in sorption, catalysis, electrical conductivity,magnetism and photochemistry. Multinuclear clusters are a kind of significantbuilding subunit in the crystal engineering of MOFs, as they have a larger size andmultiple coordination sites, which is in favor of forming high–connected andhigh–dimensional MOFs. Polyoxometalates （POMs）, one kind of multiple functionalmetal oxide clusters, have often been employed as inorganic building blocks forconstructing various MOFs due to their controllable shapes, large nanosizes, highelectronic density and oxo-riched surface. To date, a number of POM–based MOFshave been reported. However, reports on the POM–based MOFscontainingmultinuclear clusters, especially the high–dimensional mixed–valence frameworks areseldom.In this work we chose a system of Keggin POMs, Cu and Hptz to constructPOM–based MOFs containing multinuclear Cu clusters, and five new compoundswere obtained. Their structures were characterized by IR, elemental analyses, XPS,TG an d single crystal X-ray diffractions. And, the electrochemical properties wereinvestigated as well.The formulas of the five compoundsas below:[Cu^â… ₂Cu^â…¡₄（ptz）₆（OH）（H₂O）₂][PW₁₂O₄₀]·2H₂O （1）Cu^â… ₂Cu^â…¡₅（ptz）₆（OH）₂SiW₁₂O₄₀·6H₂O （2）[Cu^â… ₂Cu^â…¡₅（ptz）₆][PMoV3MoVI₉O₄₀]·8H₂O （3）[Cu^â… 5Cu^â…¡₃（ptz）₈（H2O）][HSiW₁₂O₄₀]（4）[Cu^â… ₁₀Cu^â…¡₂（ptz）₈（Cl）₃][PW¹²O₄₀]（5）Compound1exhibits a2D grid-like sheet which is composed of mixed–valencemultinuclear copper chains and PW12polyanions. Compounds2and3areisostructural, in which polyanions connect neighboring Cu–ptz layers to form a3DPOM–templated Cu–ptz framework. Compounds4and5show a3D POM–templatedCu–ptz framework, which features unprecedented multinuclear Cu double-chains in4and Cl–centered hexanuclear Cu clusters and Cl–bridged tetranuclear Cu units in5.To the best of our knowledge, Compounds1–5represent the first mixed–valenceCu–ptz frameworks based on Keggin POMs.