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

Abstract

The peroxo-bridged di-cerium(IV)-di-lithium-containing polyoxometalate [(CeIV2O2)Li2(P2W16O59)2]16 (Ce2Li2P4W32) is synthesized in a one-pot aqueous synthetic procedure and isolated as a hydrated mixed alkali salt, K13.6Na1.4Li[(CeIV2O2)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 peroxogroup 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.