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

Abstract

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 Na₁₅[Na₃⊂{M(H₂O)₄}₆{WO(H₂O)}₃(P₂W₁₂O₄₈)₃]·xH₂O (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) Å, b = 32.114(3) Å, c = 33.848(4) Å, for 1; a = 21.643(6) Å, b = 31.870(6) Å, c = 33.861(7) Å for 2. Polyoxoanions [Na₃⊂{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.