Hydrothermal Synthesis, Crystal Structures and Electrochemical Properties of Two Phosphatotungstates Containing Keggin Clusters, [Cu(2,2′-bipy)2]5[PW12O40] • 2H2O and (Hpip)3[PW12O40]

Two new phosphatotungstates containing Keggin clusters, [Cu(2,2'-bipy)(2)](5)[PW12O40] center dot 2H(2)O (1) (2,2'-bipy = 2,2'-bipyridine) and (Hpip) 3[PW12O40] (2) (pip = piperazine) have been hydrothermally synthesized and characterized by IR, element analysis and cyclic voltammogram. Compound 1 consists of one discrete Keggin polyanion [PW12O40](5-), five isolated complex cations [Cu(2,2'-bipy)2](+) and two water molecules. The organic moieties exhibit regular packing with offset aromatic-aromatic interactions between the bipys, leading to a compact supramolecular framework structure. Compound 2 is made up of one discrete Keggin polyanion [PW12O40](3-) and three pip cations. Compounds 1 and 2 were employed to fabricate bulk-modified carbon paste electrode to research on their electrochemistry properties. Their electrochemical behaviors and electrocatalysis that 1- and 2-CPEs have electrocatalytic activities toward the oxidation of nitrite. Compound 1 is in the orthorhombic system, space group Pna2(1), with a = 28.1928(9), b = 21.5479(6), c = 19.9088(6) angstrom, V = 12,094.5(6) angstrom(3) and Z = 4. Compound 2 is in the rhombo-hedral system, space group R (3) over barc, with a = 17.9191(5), c = 23.7439(9) angstrom, V = 6,602.6(4) angstrom(3) and Z = 6.