NMR study of lithium ion in nitrobenzene/water system

Abstract

The goal of this project has been to elucidate the solvation states and kinetics involved in the transfer of Li ions between nitrobenzene and water. A large interface area has been realized by confining one phase in polymer beads and suspending them in the other phase. A 2D ⁷Li-NMR spectroscopic result of such a system obtained on a 400 MHz instrument has shown that the rate of the Li ion transfer exchange between nitrobenzene and water is too fast to resolve individual solvatomers. A pair of well-resolved ⁷Li-NMR peaks corresponding to different solvation environments of Li⁺ in “wet” nitrobenzene has been observed. The most surprising result is that the ratio of those two peaks and their separation changes over a period of days, but it can be reversibly changed by mechanical disturbance, such as ultrasonication. This effect is reproducible and suggests spontaneous but slow formation of metastable solvatomers of Li⁺. Another surprising observation has been slow and irreversible incorporation of lithium ion from wet nitrobenzene into the walls of the silica-containing vessels.