Structures of the n-alkylpolyoxyethylene complexes of alkali metal ion and their ion pairs in 1,2-dichloroethane

Abstract

The structures of the alkali metal ion complexes of polyoxyethylene (POE) compounds and their ion-pairs with picrate ion (pic⁻ ) in water saturated (0.131 mol dm⁻³) and low water concentration (0.01 mol dm⁻³) 1,2-dichloroethane (1,2-DCE) were studied by means of electric conductivity, where POE compounds were linear hexa- (DEO6) and octa-oxyethylenemonododecylether (DEO8) and 18-crown-6 (18C6). The ion-pair formation constants and limiting molar conductivity of the complex ions were evaluated by the analysis of the concentration dependence of the molar conductivity. The interionic distance between the cationic complex and the picrate ion estimated from the ion-pair formation constants indicates that the metal–polyoxyethylene (POE) moiety of the DEO6 complexes has a similar structure to that of 18C6 complexes. The large interionic distances of the ion pair of the DEO8 complexes compared with those of DEO6 indicate that metal ion of DEO8 complex is spherically wrapped by the ethyleneoxide chain. The Stokes radius of the POE–metal moiety of the cationic complex was estimated from the limiting molar conductivity by correcting the effect of the dodecyl group on the conductivity. The peculiar behavior of the conductivities of the lithium complexes suggests that the structures of these complex cations are considerably distorted in both the water saturated and the low water solvents.