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.