The factors affecting on the assembly of Ag–H2biim system: size, charge or shape of polyanions?

Abstract

By introducing different polyoxotungstates into the Ag–H₂biim system, four new compounds with distinct architectures, Ag₂(H₂biim)₄(W₆O₁₉)·2H₂O (1), Ag₆(H₂biim)₆(SiW₁₂O₄₀)(OH)₂·2H₂O (2), Ag₆(H₂biim)₆(PW₁₂O₄₀)(OH)₃·H₂O (3) and Ag₆(H₂biim)₆(P₂W₁₈O₆₂)·12H₂O (4) (H₂biim = 2,2′-biimidazole), have been hydrothermally synthesized, and characterized by routine physical methods and single crystal X-ray diffraction. In compound 1, the Lindqvist type polyoxotungstate {W₆} combines with the chelate Ag–H₂biim complex forming a discrete “dumbbell-like” motif. Isostructural compounds 2 and 3 are obtained by introducing Keggin polyoxotungstates ({SiW₁₂} and {PW₁₂}, respectively), which show a 2D layer structure. The 2D layers parallel each other to form a 3D supramolecular framework. The larger Wells–Dawson polyoxotungstate {P₂W₁₈} directs the formation of compound 4, in which one 2D layer is the inversion of the neighboring ones. Furthermore, there exist infinite Ag chains in compounds 2–4, which are quite unusual in POM-based compounds. The distinction among the final four architectures is ascribed to the structure-directing effect of different polyanions. The electrochemical properties of compounds 1–4 are studied. In addition, the antibacterial properties of the four compounds against negative Escherichia coli (E. coli) and positive Staphylococcus aureus are investigated.