Potentiometric Studies on Ternary Complex Formation between Cu(II), Ni(II), Zn(II), Cd(II), nitrilotriacetic acid and amino acid

The formation of ternary complexes of the type MAB (where M = Cu(II), Ni(II), Zn(II) or Cd(II); A = nitrilotriacetic acid and B = glycine, α‐alanine or dl‐aspartic acid) has been shown by potentiometric studies. The nature of titration curves indicates that the secondary ligand B is added stepwise to the initially formed metal nitrilotriacetates. The formation constants (log KMAB) and the free energies of formation (ΔF°) of the mixed complexes have been calculated at 25 ± 1 °C and m̈ = 0.10 (KNO3) at different pH values. The formation constants of the resulting 1:1:1 ternary complexes follow the order Cu(II) > Ni(II) > Zn(II) > Cd(II).