Revisiting the Three Vanadium Sandwich-Type Polyoxometalates: Structures, Solution Behavior, and Redox Properties

• Published in: Inorganic chemistry Vol. 61; no. 21; pp. 8309 - 8319
• Main Authors: Bamba, Ibrahima Fa, Falaise, Clément, Marrot, Jérôme, Gbassi, Gildas K., Atheba, Patrick, Guillot, Régis, Haouas, Mohamed, Cadot, Emmanuel
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 30-05-2022
• Subjects: Chemical Sciences; Inorganic chemistry; Material chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.2c00776

It is well known that the trivacant anions α-B–[XW9O33]9– react with vanadyl ions to give the sandwich-type polyoxometalates [(VIVO)3(XW9O33)2]12– with X = AsIII or SbIII. Nevertheless, the oxidized derivatives have been obtained selectively by electrochemical oxidation from the fully reduced derivatives [(VIVO)3(XW9O33)2]12– allowing full characterization both in solution using UV–vis and multinuclear (17O, 51V, and 183W) NMR spectroscopies and in the solid state by single-crystal X-ray diffraction. Structural analysis of the oxidized [(VVO)3(XW9O33)2]9– polyanions is consistent with the idealized D 3h symmetry, while solution studies reveal a fair hydrolytic stability in a wide pH range from 0 to 6. Besides, the D 3h polyanions either as reduced or oxidized forms [(VO)3(AsW9O33)2]9/12– have been identified as the thermodynamic product that results from the conversion of the C 2v polyanion [(H2O)­(VO)3(AsW9O33)2]9/12– through moderate heating. Conversely, the SbIII-containing derivative gives exclusively the D 3h polyanion, probably either due to the extended lone pair of the trigonal SbIII heterogroup that prevents the formation of the C 2v arrangement or the lability of the oxo-metalate bonds that favor chemical exchange. The electrochemical studies of sandwich-type polyoxometalates revealed that each {VO} group gives rise to a one-electron transfer process. At last, the redox properties appear strongly altered in the 0.3–5 pH range, consistent with proton-coupled electron transfers.