The aggregation of dichlorobis(N-hexylethylenediamine)zinc(II) in water and water/chloroform mixed solvents

The aggregation of a surfactant metal complex, dichlorobis(N-hexylethylenediamine)zinc(II) (= [ZnCl2(hex-en)(2)]), was studied in such solvents as water, methanol (or water-methanol mixed), and chloroform (or water-containing chloroform). This complex was readily dissolved in water to form aggregates extensively, and was also very soluble in water-containing chloroform to give reversed-type aggregates. In dilute aqueous solutions, the complex was hydrolyzed and precipitated, while the solution was stable at concentrations above 0.25 mol kg(-1) where the complex aggregates considerably. Precipitation was prevented by the addition of NaCl; this effect can be attributed to chloride-ion binding, The aggregation behavior in solutions was investigated by measuring the self-diffusion coefficients for the complex and of the vapor pressure depressions. The degrees of aggregation of the aqueous and water-containing chloroform solutions were in a similar manner at higher concentrations, although the critical concentration for aggregation in the aqueous solution was considerably smaller than in the chloroform solution. The hydration mode of this surfactant complex is discussed in comparison to the D2O longitudinal relaxations between the aqueous solutions and the water-containing chloroform solutions.