Complexation equilibria of some sulphoazoxines. Part VIII. Complexes of SNAZOXS with copper(II), lead(II) and cadmium(II) ions evaluated by regression analysis of potentiometric data

Abstract

The reactions of oligomers of the sulphoazoxine SNAZOXS with H⁺, Pb²⁺, Cd²⁺ and Cu²⁺ ions were studied potentiometrically at 298 K in aqueous solutions. The protonation constants of the ligand oligomers L₂H₄^2–, L₂H₃^3–, L₂H₂^4– and L₂H^5– and the formation constants of several metal complexes were calculated with the aid of the program MINIQUAD. The chemical models were selected on the basis of a critical evaluation of the least-squares results and of a goodness-of-fit test by the statistical analysis of residuals. Whereas Cu²⁺ and Cd²⁺ ions form CuL^–, CuLH, CuL₂^4– and CuL₂H^3– complexes (Cu can be replaced with Cd), the Pb²⁺ ion forms PbLH, PbL₂^4–, PbL₂H^3– and Pb₂L₃^5– complexes.