Oxygen-exchange reactions in nanometer-size hexaniobate clusters

GEOC 103

Jay R. Black1, May Nyman, mdnyman@sandia.gov2, and William H. Casey1. (1) Department of Chemistry and Department of Geology, University of California, 350 Chemistry Bldg, Shields Avenue, Davis, CA 95616, (2) Geochemistry Department, Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185
Nanometer-sized clusters are proving useful in unraveling pathways for oxygen exchanges at the aqueous interface because they are small enough to determine reactions at specific sites, yet large enough to resemble fragments of larger structures. Toward this end, the reactivity of the hexaniobate polyoxoanion ([HxNb6O19](8-x)-, x = 0-3) was investigated using a number of techniques to determine its reactivity and stability over the pH range 8-14. 17O-NMR was employed to determine the rates of exchange of the bridging, terminal and the central oxygen sites as a function of pH and temperature. Besides the rate data, with decreasing pH, fractions of the hexaniobate ion polymerize to form larger clusters, one of which has been tentatively identified as a decaniobate ion. Capillary electrophoresis chromatography confirms that larger clusters form with time and the 17O-NMR indicates that the smaller molecule does not fully dissociate as polymerization proceeds.
 

The Structure and Reactivity of Nanoparticles in the Environment
8:50 AM-11:55 AM, Wednesday, 13 September 2006 Moscone Center -- Room 262, Oral

Division of Geochemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006