NMR Determination of the Hydration Numbers of Cations in Aqueous Perchlorate Solution

摘要

In an aqueous solution of a paramagnetic ion which exchanges water rapidly between its first coordination sphere and the solvent, a single oxygenhyphen;17 NMR signal is observed shifted from its normal position in pure H2O. The magnitude of the shift is a measure of the ratio of the paramagnetic ion concentration to total (labile) water in the system. If a second ion for which the first coordination sphere water is sufficiently nonlabile (tgr;sim;10mdash;4sec) is added to the system, the decrease in the water available to interact with paramagnetic ions due to water retained in the nonlabile environment will produce an increase in the shift in the labile H217O resonance by the paramagnetic ion. The application of this ``molal shift'' method to the determination of the hydration numbers of certain diamagnetic and paramagnetic cations in aqueous solutions is demonstrated and discussed.