Highly Shielded Peroxo-Cerium(IV)-Containing Polyoxometalate: Synthesis, Structure, and Oxidative Studies

Abstract

The peroxo-bridged di-cerium(IV)-di-lithium-containing polyoxometalate [(Ce^IV₂O₂)Li₂(P₂W₁₆O₅₉)₂]¹⁶⁻ (Ce₂Li₂P₄W₃₂) is synthesized in a one-pot aqueous synthetic procedure and isolated as a hydrated mixed alkali salt, K_13.6Na_1.4Li[(Ce^IV₂O₂)Li₂(P₂W₁₆O₅₉)₂]·32H₂O (KNaLi-Ce₂Li₂P₄W₃₂). The novel polyanion Ce₂Li₂P₄W₃₂ comprises a side-on peroxo-group bridging two cerium(IV) and two lithium ions, which are encapsulated between two dilacunary, face-on {P₂W₁₆} Wells–Dawson units, with a vacant site in each of the two belts. The polyanion Ce₂Li₂P₄W₃₂ is characterized in the solid state by single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and Raman spectroscopy and in solution by ³¹P NMR and Raman spectroscopy, respectively. Ce₂Li₂P₄W₃₂ and the peroxo-group are shown to be highly stable in a large pH range and up to almost boiling temperatures, but at the same time the polyanion is reactive toward oxidation of triphenylphosphine, involving the peroxo group and the cerium(IV) centers.