Potentiometric and conductometric studies on the binary and mixed ligand complexes in solution: M-II-dipicolinic acid glycine systems

The binary and mixed ligand complexes of some alkaline earth and transition metal (II) ions with dipicolinic acid (DPA) as a primary ligand and the biologically important secondary ligand (glycine), were studied using potentiometric technique. The acidity constants of the ligands were determined and used for determining the stability constants of the complexes formed in aqueous solutions under the experimental conditions (t = 25 degrees C, mu = 0.1 M NaNO3). The dissociation constants of DPA were also determined in various water + dioxane mixtures under the same experimental conditions. It is concluded that a pronounced change in the pK values is observed as the solvent is enriched in dioxane. The values of Delta logK have been evaluated and discussed. In addition, the chelation mode of ternary complexes was ascertained by conductivity measurements. (C) 1997 Elsevier Science B.V.