A Conductance Study of 1 : 1 Complexes of 1,2-Bis[2-(2-methoxyethoxy)ethoxy]benzene (Noncyclic Polyether) with Alkali Metal Ions in Nonaqueous Solvents

Conductivities of alkali metal salts in the presence of 1,2-bis[2-(2-methoxyethoxy)ethoxy]benzene (AC·B18C6), which is a linear counterpart of benzo-18-crown-6 (B18C6), were measured at 25 °C in acetonitrile, propylene carbonate, and methanol. Formation constants and limiting ionic molar conductivities of the 1 : 1 AC·B18C6–alkali metal ion complexes were determined. Selectivity of AC·B18C6 for alkali metal ions is lower than that of B18C6. The selectivity order of AC·B18C6 for K+, Rb+, and Cs+ is consistent entirely with that of B18C6 (K+>Rb+>Cs+), but the selectivity order of AC·B18C6 for Na+ differs from that of B18C6. The AC·B18C6–alkali metal ion complex is less stable than the corresponding B18C6 complex. The AC·B18C6 complex may be entropy-destabilized due to the two flexible arms. The AC·B18C6–alkali metal ion complex is more mobile than the corresponding B18C6 complex; the mobility of the AC·B18C6 complex is less sensitive to a variety of the alkali metal ions in the complexes than that of the B18C6 complex. This indicates that the alkali metal ion in the AC·B18C6 complex is coordinated with the two arms and the surface charge of the alkali metal ion in the AC·B18C6 complex is more effectively shielded than that in the B18C6 complex.