Crystal structure and properties of a new sandwich heteropolytungstate Na6(C5N2H7){[Na(H2O)2]3Co(H2O)5[CO(H2O)]3(AsW9O33)2}•27H2O

A new sandwich heteropolytungstate Na-6(C5N2H7){[Na(H2O)(2)](3)Co(H2O)(5)[Co(H2O)](3)(ASW(9)O(33))(2)}center dot 27H(2)O was synthesized by the reaction of Na2WO4 center dot 2H(2)O, NaAsO2, CoCl2 center dot 6H(2)O and p-aminopyridine (C5H7N2) in pH=7.5 aqueous solution. The single crystal X-ray diffraction study shows that the crystal belongs to triclinic system, space group P (1) over bar, with a=1.3276(8) nm, b=1.7581(10) nm, c=2.4381(14) nm, alpha=70.954(9)degrees, beta=86.663(9)degrees, gamma=72.885(9)degrees, V=5.136(5) nm(3), Z=2, R-1=0.0608, wR(2)= 0.0848 [1>2 sigma(I)]. The structure of anion {[Na(H2O)(2)](3)Co(H2O)(5)[Co(H2O)](3)(ASW(9)O(33))(2)}(7-) reveals a sandwich arrangement of two {alpha-B-AsW9} moieties enclosing three Co(H2O)(2+) and three Na(H2O)(2)(+), and another Co(H2O)(5)(2+) connects with one terminal oxygen of {[Na(H2O)(2)](3)[Co(H2O)](3)(AsW9O33)(2)}(9-). There are two kinds of coordination numbers of Co2+ in the polyanion, 5 and 6. The title compound was also characterized by IR, UV-Vis and TG-DSC. The formation condition of the the title compound was discussed. It was shown that the title compound was much more effective than Na2WO4 center dot 2H(2)O or CoCl2 center dot 6H(2)O for the catalytic oxidation of acetaldehyde with hydrogen peroxide in an aqueous solution.