Low-Viscosity Concentrated Lithium Chloride Solution with Unsymmetrical Ditopic Receptors in Organic Solvents

Ditopic receptors with different terminal substituents on urea moieties linked with ether groups are prepared, and the solubilization of high-concentration LiCl by the receptors in acetonitrile is evaluated. The unsymmetrical receptors have higher solubility than the corresponding symmetrical receptors, and the complex solution of the receptor and LiCl shows reduced viscosity resulting in improved ionic conductivity, as well as suppression of solidification. In addition, selective solid-liquid extraction of LiCl by the receptors is demonstrated by the ¹H NMR spectra compared to other alkaline and alkali earth chlorides. Density functional theory calculations suggest that this selectivity is due to the shape complementarity of the cation recognition site and the cooperative anion recognition by the two urea groups. These properties suggest that the unsymmetrical ditopic receptors can be applied to an electrolyte and LiCl extractant.