Nuclear Magnetic Resonance Studies on Hydration of Cations

Abstract

A preliminary study of the O¹⁷ NMR spectra of aqueous solutions has shown that it is possible to distinguish solvent water from water in the hydration sphere of certain cations. For certain ions the hydration water of which is sufficiently nonlabile (lifetime for exchange >10^—4 sec), it is possible to display the hydration water as a separate NMR peak when the solvent peak is shifted by addition of a paramagnetic ion. A method is suggested for determining the hydration number of such cations by measuring the change in the water available to interact with the paramagnetic ions due to water retained in the hydration sphere of the cations. The enrichment level of the O¹⁷ at present available does not permit precise determination of the hydration number, but the results are not incompatible with reasonable values.