NMR relaxation and microstructure of aqueous electrolyte solutions

A method is presented for determining microstructural parameters (coordination numbers of ions, mobilities of solvent molecules) of diamagnetic aqueous solutions from NMR relaxation data; it is based on the analysis of the concentration and temperature dependence of the relaxation rates of various nuclei belonging to solvent molecules and ions. The results, obtained for some 20 different ions, make it possibile to formulate several laws which govern the formation of ion hydration shells: (i) monatomic ions are surrounded by the highly symmetrical shells; (ii) multiatomic ions form the hydration shells in accordance with the number of possible intermolecular bonds; and (iii) hydration shells of cations usually have second layers, but there are no distinguishable second layers near the anions.