Rates of oxygen exchange between the [HxNb6O 19]8-x(aq) Lindqvist ion and aqueous solutions

Abstract

Oxygen-isotope-exchange rates were measured between sites in the Lindqvist-type [HxNb6O19]8-x) (aq) polyoxoanion and aqueous solution as a function of pH and temperature. The ion has a central μ6-O that is inert to exchange, 12 μ2-O(H), and 6 η-O. The potassium salt of this ion is recrystallized in 17O-enriched water to 17O-label the anion, which is then redissolved into isotopically normal water so that the 17O NMR signals from structural oxygens can be followed as a function of time. Because the central μ6-O retains its 17O signal throughout the experiments, it is clear that the polyoxoanion remains intact during isotopic equilibration of the other structural oxygens. At pH conditions wher..