Nuclear magnetic relaxation studies of preferential solvation in electrolyte solutions. Another indirect method using only solvent magnetic interactions

Abstract

In the mixture ROH/H₂O (R = C_nD_2n+1) an intramolecular proton relaxation contribution due to magnetic dipole interaction only occurs in the water molecule. If the water molecules are preferentially bound to a hydrated cation undergoing relatively slow molecular motions, then only this intramolecular part reflects the slow motion. This principle was used to study preferential solvation of ions in MeOH + H₂O mixtures. From the experimental results reported, it is deduced that Mg²⁺ is preferentially hydrated whereas, in agreement with the theory, for K⁺ and Rb⁺ the dynamical effect of preferential solvation is so small that it cannot be detected with the present method.