1Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, P.O. Box 91735-654, I.R. IRAN
2Department of Chemistry, Faculty of Sciences, Birjand University, Birjand, I.R. IRAN
A Competitive spectrophotometric method has been used for the study of complexation between Cu2+, Zn2+ and Cd2+ (M) and 18-crown-6(18C6, B) in methanol using 4-(2-thiazolylazo) resorcinol (TAR, HL) as the colorimetric complexant. Absorption spectra of the species in the M-TAR-18 C6 system at a various concentrations of 18C6 showed no formation of ternary complex, MLB, and the stoichiometry of the resulting complexes was found to be 1:1 under the condition used. The formation constants of both types of complexes (ML and MB) were determined using the conditional formation constant of ML complexes at constant acidity in the absence (KML') and presence (KM''L') of 18C6. The results showed that the KMB values increased in the order of Cu2+<Zn2+<Cd2+, the KMB values were comparable with those reported previously.