Potentiometric Studies on Stepwise Mixed Ligand Complex Formation Copper(II)-Iminodiacetic Acid-Hydroxy Acid

Abstract

Potentiometric studies are described for mixed ligand complex formation of copper(II) with iminodiacetic acid (IMDA) as primary ligand and certain hydroxy acids, such as salicylic acid (SA), 5-sulphosalicylic acid (SSA), tiron (3.5-pyrocatechol disulphonic acid PDS) and chromotropic salt (3,6-disulpho-1,8-dihydroxynaphthalene disodium salt CS) as secondary ligands. The pH titrations of the reaction mixtures containing copper nitrate, iminodiacetic acid and one of the secondary ligands in equimolar concentrations indicated the formation of 1:1:1 mixed ligand complex. From the nature of the titration curves it appears that in the lower buffer region 1:1 copper (II) -iminodiacetic acid complex is initially formed and the formation of mixed ligand complex takes place only after the combination with the primary ligand is complete. However, in the case of Cu (II) -IMDA-HQSA system it appears that the mixed ligand complex is not formed stepwise, but the chelation with both the ligands takes place simultaneously. The formation constants (log K) of the mixed ligand chelates of Cu (II) -IMDA-SA. Cu (II)-IMDA-SSA. Cu (II) -IMDA-Tiron and Cu (II) -IMDA-CS system have been calculated. All the titrations were carried out at room temperature (25±1°C) using 5 × 10 3 м concentration of metal and ligand ions (μ= 0.1) with the help of potassium nitrate.