Two hexa-TM-containing (TM = Co2+ and Ni2+) {P2W12}-based trimeric tungstophosphates

摘要

Reactions of hexavacant polyoxotungstates [H2P2W12O48](12-) ({P2W12}) with transition-metal (TM), and alkali-metal ions lead to the isolation of two hexa-TM-containing polyoxotungstates Na-15[Na-3 subset of{M(H2O)(4)}(6){WO(H2O)}(3)(P2W12O48)(3)]center dot xH(2)O (M = Co2+, x = 109 for 1; M = Ni2+, x = 110 for 2). Single-crystal X-ray diffraction analysis revealed that compounds 1 and 2 both crystallized in the orthorhombic system, space group Cmcm, with lattice constants a = 21.353(3) angstrom, b = 32.114(3) angstrom, c = 33.848(4) angstrom, for 1; a = 21.643(6) angstrom, b = 31.870(6) angstrom, c = 33.861(7) angstrom for 2. Polyoxoanions [Na-3 subset of{M(H2O)(4)}(6){WO(H2O)}(3)(P2W12O48)(3)](15-) in 1 and 2 exhibit a crown-type structure composed of a [{WO(H2O)}(3)(P2W12O48)(3)](18-) (abbreviated as {P6W39}) shell encapsulating six TM ions and three Na+ cations. Polyoxoanions 1 and 2 represent the. first hexa-TM-containing {P2W12}-based trimeric POMs, which offer new examples with the potentially aqua-ligand-induced capability of "trapping" metal ions in the {P6W39} shell. Electrocatalytic studies show that compounds 1 and 2 display electrocatalytic activity to reduce nitrite.