Polarographic Study of the Interaction
of Tl⁺, Pb²⁺, and Cd²⁺ Cations with 18-Crown-6
in Binary Nonaqueous Solvents¹

M. Chamsaz, Gh. Rounaghi, and M. R. Sovizi

Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran

Received December 16, 2003

Abstract—The complexation reaction between Tl⁺, Pb²⁺, and Cd²⁺ cations with macrocyclic ligand 18-crown-6
(18C6) was studied in methanol (MeOH)/acetonitrile (AN), methanol/dimethylformamide (DMF), methanol/ben-
zene, and methanol/benzonitrile (BN) binary mixtures at 18°C using DC and differential-pulse (DP) polaro-
graphic techniques. The results obtained in this study show that the stability of the complexes depends on the
nature and composition of the mixed solvents, and, with the exception of 18C6–Tl⁺ complex in MeOH/AN
binary systems, there is an inverse relationship between the Gutmann donor number (DN) of the solvents and
the stability of complexes. The stoichiometry of the complexes in most of the systems was found to be 1 : 1,
but, in the case of complexation of Tl⁺ cation with 18C6 in MeOH/BN binary mixtures and complexation of
Cd²⁺ cation with 18C6 in MeOH, 1 : 2 (M) and 2 : 1 (M₂L⁴⁺) complexes were formed, respectively. The
selectivity order of the ligand for cations was found to be Pb²⁺ > Tl⁺ > Cd²⁺ in all the systems. The variations
of vs. the composition of the mixed solvents show a linear behavior for some systems and a nonlinear
trend for other systems.

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