Syntheses, crystal structure and properties of the dimeric [(CH<sub>3</sub>)<sub>4</sub>N]<sub>4</sub>[PW<sub>11</sub>O<sub>39</sub>H<sub>2</sub>La(H<sub>2</sub>O)<sub>4</sub>]<sub>2</sub> · 3H<sub>2</sub>O

Abstract

2:2-type dimeric [(CH₃)₄N]₄[PW₁₁O₃₉H₂La(H₂O)₄]₂·3H₂O was successfully synthesized by reaction of the monovacant Keggin structure α-Na₇PW₁₁O₃₉·<italic>n</italic>H₂O with LaCl₃·7H₂O and (CH₃)₄NCl in aqueous solution. Single crystals of this compound were analyzed by X-ray crystallography and found to be in the triclinic space group <italic>P</italic>1 with the following parameters: <italic>a</italic> = 1.35383(10) nm, <italic>b</italic> = 1.60687(12) nm, <italic>c</italic>= 1.86958(13) nm, α= 65.9630(10)°, β = 83.1650(10)°, γ= 83.6780(10)°, <italic>Z</italic> = 1, <italic>R</italic>1 = 0.0589, <italic>wR</italic>2 = 0.1447. The dimeric polyoxoanion [{(α-PW₁₁O₃₉H₂)La(H₂O)₄}₂]^4– consisted of two [α-PW₁₁O₃₉]^7- subunits linked together by two [La(H₂O)₄]³⁺ cations. The nine-coordinate La³⁺ cation was incorporated in the vacant site of the [α-PW₁₁O₃₉]^7- subunit, which adopted monocapped square antiprismatic coordination geometry. Thermogravimetric analysis exhibited two weight loss steps between 25 and 600°C; cyclic voltammetry indicated that two reversible single-electron reductions of the synthesized compound occurred in aqueous solution at pH 4.3.