Oxygen-17 NMR study of aqueous peroxotungstates.
Aqueous peroxotungstates have been studied from pH 0.5 to 9.0, over a range of peroxide concentrations. Although equilibria are not always established, many anions can be identified by 17O NMR because the ratio of deltaO(W anion)/deltaO(known Mo anion) is consistently 79 +/- 3%. They are [WO3(HO2)]-; [WO(OH)(O2)2]-; [WO(OH2)(O2)2]0; [W2O3(O2)4]2-; [W2O3(OH)(O2)4]3-; [W4O12(O2)2]4-; [W7O23(O2)]6- and [W7O22(O2)2]6-. Their pKa values, where measurable, are about 2 units lower than the corresponding peroxomolybdates, e.g. 0.0 for [WO(OH2)(O2)2]0 and 8.0 for [W2O3(O2)4]2-. Other peroxotungstate species are also present but can only be broadly identified. These include Keggin structures with relatively low peroxo content, and a very unsymmetrical anion appearing at pH ca. 7 that bears no obvious structural relationship to any species previously reported. The main product from the reaction of powdered W metal with 30% aqueous peroxide is provisionally identified as the symmetrical anion [W6O13(OH)2(OH2)2(O2)5]2-, although other minor species are also formed, probably having fewer peroxo substituents.
Howarth
Oliver W
OW
Department of Chemistry, University of Warwick, Coventry, UKCV4 7AL.
D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D015394:Molecular Structure; D010103:Oxygen Isotopes; D010545:Peroxides / Q000737:chemistry; D017973:Tungsten Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D010103:Oxygen Isotopes; D010545:Peroxides; D017973:Tungsten Compounds; D014867:Water