THE SHORT-RANGE STRUCTURE AROUND LI+ IN HIGHLY CONCENTRATED AQUEOUS LIBR SOLUTIONS

Neutron diffraction measurements have been carried out on aqueous 10, 25, and 33 mol% LiBr solutions. The Li-6/Li-7 isotopic substitution te chnique was applied to determine the local structure around Li+ in the se solutions. The least-squares fitting analysis was successfully adop ted both for the observed Li+ difference interference function, Delta( Li)(Q), and for the Li+ distribution function G(Li)(r). The nearest ne ighbor Li+... O distance in the solutions was obtained to be 1.96+/-0. 02 Angstrom, which agrees well with that reported in previous neutron diffraction studies. The average hydration number of Li+ decreases fro m ca. 6 for the 10 mol% LiBr solution to ca. 4 for the 25 mol% LiBr so lution. The tetrahedral hydration structure around Li+ appeared to sta y even in the 33 mol% LiBr solution. The Li+... Br- correlation was fo und at 3.4 Angstrom in the 33 mol% LiBr solution. This value rather su ggests the formation of the solvent-shared ion pair, Li+... D2O ... Br -.