Diffraction pattern and structure of aqueous lithium chloride solutions

Abstract

We present the first extensive study of an ionic solution by both neutron and x-ray diffraction. Pure water and aqueous LiCl at concentrations to saturation (mole ratio D2O:LiCl=3) have been examined at room temperature by both methods. This extensive study reduces greatly the nonuniqueness of interpretation usually associated with diffraction data from liquids. All data are shown to be consistent with a simple model involving only nearest neighbor interactions. In the pure liquid and in dilute solutions, the molecular structure is observed to be close to that found for the gas molecule. The tetrahedral coordination of oxygen atoms around each water is clearly shown, with deuterium atoms located near the O–O lines. This basic water structure gradually diminishes with increasing LiCl concentration, and is unobserved at mole ratios of 10 or lower. The coordination of oxygen atoms about Cl− appears to be octahedral on the average, with a deuterium atom near each connecting line. The coordination around Li+ appears to be tetrahedral; the orientation of the coordinated water molecule is such that Li and 2D occupy three tetrahedral positions about oxygen.