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Oxygen-Isotope Exchange Rates for Three Isostructural Polyoxometalate Ions
2010 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 14, 5264-5272 p.Article in journal (Refereed) Published
Abstract [en]

We compare oxygen-isotope exchange rates for all structural oxygens in three polyoxoniobate ions that differ by systematic metal substitutions of Ti(IV) -> Nb(V). The [H(x)Nb(10)O(28)]((6-x)-), [H(x)TiNb(9)O(28)]((7-x)-), and [H(x)Ti(2)Nb(8)O(28)]((8 -x)-) ions are all isostructural yet have different Bronsted properties. Rates for sites within a particular molecule in the series differ by at least similar to 10(4), but the relative reactivities of the oxygen sites rank in nearly the same relative order for all ions in the series. Within a single ion, most structural oxygens exhibit rates of isotopic exchange that vary similarly with pH, indicating that each structure responds as a whole to changes in pH. Across the series of molecules, however, the pH dependencies for isotope exchanges and dissociation are distinctly different, reflecting different contributions from proton- or base-enhanced pathways. The proton-enhanced pathway for isotope exchange dominates at most pH conditions for the [H(x)Ti(2)Nb(8)O(28)]((8 -x)-) ion, but the base-enhanced pathways are increasingly important for the [H(x)TiNb(9)O(28)]((7-x)-) and [H(x)Nb(10)O(28)]((6-x)-) structures at higher pH. The local effect of Ti(IV) substitution could be assessed by comparing rates for structurally similar oxygens on each side of the [H(x)TiNb(9)O(28)]((7-x)-) ion and is surprisingly small. Interestingly, these nanometer-size structures seem to manifest the same general averaged amphoteric chemistry that is familiar for other reactions affecting oxides in water, including interface dissolution by proton- and hydroxyl-enhanced pathways.

Place, publisher, year, edition, pages
2010. Vol. 132, no 14, 5264-5272 p.
National Category
Inorganic Chemistry Physical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-129139DOI: 10.1021/ja100490nISI: 000276553700056PubMedID: 20302304OAI: oai:DiVA.org:umu-129139DiVA: diva2:1058598
Available from: 2016-12-21 Created: 2016-12-21 Last updated: 2017-02-09Bibliographically approved

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Ohlin, C. Andre
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