Three Polyoxometalate-Based Coordination Polymers Constructed from the Same Dimetallic Cyclic Building Block

The reactions of silicotungstate, 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (3-bpo), and copper, cobalt, or nickel acetate under hydrothermal condition yield the three compounds [(SiW12O40)Cu-2(3-bpo)(2)(C5H4NCOOH)(2)]center dot H2O (1), [(SiW12O40)-Co-2(3-bpo)(2)(C5H4NCOOH)(2)(H2O)(2)]center dot 2H(2)O (2), and [(SiW12O40)-Ni-2(3-bpo)(2)(C5H4NCOOH)(2)(H2O)(2)]center dot 3H(2)O (3), respectively, in which the nicotinic acid ligands are generated from the in situ decomposition of 3-bpo during the hydrothermal process. In the three structures, the polyoxometalate (POM) serves as the center and is imbedded within the dimetallic cyclic [M-2(3-bpo)(2)(C5H4NCOOH)(2)](4+) moiety through coordination bonds to form infinite one-dimensional (1D) supramolecular snadwich-like structures. Owing to the difference in the metal ions, the packing style of [Cu-2(3-bpo)(2)(C5H4NCOOH)(2)](4+) is different from that of [M-2(3-bpo)(2)(C5H4NCOOH)(2)](4+) (M = Co, Ni). The electrochemical behaviors of compounds 1-3 were studied by cyclic voltammetry.