X-ray diffraction studies of alkali halide solutions

Alkali halide aqueous solutions (LiCl, LiBr, NaCl, NaBr) have been investigated by X-ray diffraction in order to clarify the structural features of these systems (the existence of ordered local structures, their stability, geometry, etc.). The cation-H₂O interaction is particularly evident for the Li⁺ ions, for which a well resolved peak at 2.1 Å is apparent in the correlation function. It is shown that the ions give rise to a considerable disturbance of the solvent structure, in fact the `order range' in the solutions appears to be shorter than in pure water. The high coordination numbers of the Cl^- and Br^- ions could be due to close packing of solvent molecules or hydrated cations around the anions.