DIRECT CORRELATION BETWEEN LITHIUM CATION AND CARBOXYL ANION IN HIGHLY CONCENTRATED AQUEOUS-SOLUTION

Time-of-flight neutron diffraction measurements have been carried out for aqueous solutions at about 20 mol% CD3COOLi. The isotopic difference method has been used to determine the distribution functions G(Li)BAR(r) around Li+ by changing the isotopic composition of Li nuclei. A model for the environment around Li+ is proposed from analysis of the first and second peaks in G(Li)BAR(r). We propose direct correlations between Li+ and two oxygen atoms in CD3COO- on the grounds of a deficiency in water molecules hydrated around Li+. Three oxygen atoms of water molecules and two oxygen atoms of an acetate ion are located at 1.96 angstrom and at ca. 2.7 angstrom, respectively. Thus, the hydration number of Li+ is 3.0 +/- 0.3: an anion of CD3COO- is located across and over the first hydration shell.