Rate of water exchange between Al(C{sub 2}O{sub 4})(H{sub 2}O){sub 4}{sup +} (aq) complexes and aqueous solutions determined by {sup 17}O-NMR spectroscopy
- Univ. of California, Davis, CA (United States)
Substitution of an oxalate molecule for two inner-coordination-sphere waters of Al(H{sub 2}O){sub 6}{sup 3+} (aq) enhances, by a factor of {approx}10{sup 2}, the rate of exchange of water molecules from the inner-coordination sphere to the bulk solution. The rate parameters for chemical exchange are: k{sub ex}{sup 298} = 109 s{sup -1}, {delta}H{sup ++} = 68.9 {+-} 2.4 kJ/mol, and {delta}S{sup ++} = 25.3 {+-} 6.7 J/mol/K, measured via dynamic {sup 17}O-NMR. This reactivity enhancement of coordinated waters by oxalate results from a change in bonding between Al(III) and oxygens throughout the complex upon ligation by oxalate. A similar process has been proposed to explain ligand-enhanced dissolution of oxide minerals where a stable adsorbate increases the flux of metals from a surface. These new rate coefficients for aluminum-oxalate complexes, along with previous work on aluminum-fluoride complexes, show a correlation with the respective equilibrium constants similar to that obtained by Ludwig et al. 34 refs., 6 figs., 2 tabs.
- DOE Contract Number:
- FG03-96ER14629
- OSTI ID:
- 617824
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 61, Issue 23; Other Information: PBD: Dec 1997
- Country of Publication:
- United States
- Language:
- English
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