Complexation of Zinc(II) and Cadmium(II) by Hydroxyethyl- and Bis(hydroxyethyl)-1,4,7-triazacyclononane in Water

Abstract

The complexation of Zn²⁺ by hydroxyethyl- and bis(hydroxyethyl)-1,4,7-triazacyclononane ((2) and (3)) in aqueous solution at 298.2 K and I = 0.10 mol dm⁻³ (NaNO₃) is characterized by log(K/dm³ mol⁻¹) = 10.45 ± 0.05 and 11.32 ± 0.02 and a deprotonation assigned to coordinated water is characterized by pK_a = 8.87 ± 0.11 and 8.50 ± 0.03, respectively. For the analogous Cd²⁺ complexes log(K/dm³ mol⁻¹) = 8.74 ± 0.02 and 9.79 ± 0.02, respectively, and no deprotonation of coordinated water is detected. The synthesis of (2) is described.