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

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)Cu2(3-bpo)2(C5H4NCOOH)2]·H2O (1), [(SiW12O40)Co2(3-bpo)2(C5H4NCOOH)2(H2O)2]·2H2O (2), and [(SiW12O40)Ni2(3-bpo)2(C5H4NCOOH)2(H2O)2]·3H2O (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 [M2(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 [Cu2(3-bpo)2(C5H4NCOOH)2]4+ is different from that of [M2(3-bpo)2(C5H4NCOOH)2]4+ (M = Co, Ni). The electrochemical behaviors of compounds 1–3 were studied by cyclic voltammetry.