2D and 3D Polymeric Wells−Dawson Polyoxometelates: Synthesis, Crystal Structures, and Cyclic Voltammetry of [(M(H2O)4)x][H6−2xP2W18−nMonO62] (M = CuII, CoII, NiII)

Abstract

The synthesis, X-ray crystal structures, cyclic voltammetry, and IR and (31)P NMR characterizations of five new Wells-Dawson-type polyoxometalates are reported, the formulas of which being [(Cu(H(2)O)(4))(2.5)][HP(2)W(18)O(62)].11.33H(2)O (4), [(Cu(H(2)O)(4))(2.4)][H(1.2)P(2)W(12)Mo(6)O(62)].11.4H(2)O (5), [(Cu(H(2)O)(4))(2.3)][H(1.4)P(2)W(15)Mo(3)O(62)].10.1H(2)O (6), [Co(H(2)O)(4))(2.3)][H(1.4)P(2)W(14)Mo(4)O(62)].18.8H(2)O (7), and [Ni(H(2)O)(4))(1.85)][H(2.3)P(2)W(15)Mo(3)O(62)].20.6H(2)O (8). These compounds are obtained as crystalline materials from the corresponding acids by substitution of a transition metal in aqueous solution. Compounds 4, 5, and 6 are isostructural; their crystal structure consists of 2D polymeric hexagonal layers where each Wells-Dawson anion is connected to six neighbors by [CuO(6)] octahedra. On the other hand, compounds 7 and 8, which are also isostructural, present a 3D structure where the Mo-substituted [P(2)W(14)Mo(4)O(62)] units are connected by [MO(6)] octahedra (M = Co(II), Ni(II)). Different types of substitution modes of Mo ions are observed within polyanions. Cyclic voltammetry shows that Cu(II) derivatives have similar behavior but different from that of the starting compounds. No electrochemical activity has been detected for the Ni-containing compound 8.