Department of Chemistry, University of Calcutta, University College of Science, 92, A PC Road! Kolkata-700 009, India E-mail gurunath@cucc emet Fax 91-33-2413222/-3519755 Bengal Chemicals and Pharmaceutical Works, Kolkata-700 009, India Manuscript received 24 November 2000 Potentiametric investigation on the coniplex foi matioh equilibria of Cull with N-benzenesulfonyl derivatives of some dipeptides, viz glycylglycine, glsicyl-β-alanine and β-alanylglycine, hereafter, abbreviated as NBSGG, NBSGB and NBSBG (AH2) respectively, in the presence of typical secondary ligands, viz acetate (ac-), 2-methylbenzimidaione (bz), glytinate. (glv-) and bipyridine (bipy), hereafter, B, provides evidence of formation of varieties of binary and ternary complexes of the types Cu(AIH), Cu(H 1AH), Cu(H 1A), Cu(H-1A)(OH), Cu(B), Cu(B)(AH), Cu(B)(H 1AH) and Cu(B)(H 1A) Stability constants of the complexes at 25 ± 1°, in aqueous solution at a constant ionic strength, I = 0 1 M (NaNO3) have been determined and the complex formation equilibria elucidated on the basis of speciation curves fhe sulfonamidodipeptide ligands ( AH2) provide three coordinating groups -COOH, -CONH-, and -SO2NH , and show ambidentism in forming the binary and the tel nary complexes depending upon the denticity, a-basicity and z-acidity of the B-ligands the ternary complexes are found to be stable in the intermediate pH range (5-8) Aboxe pH 8, the mixed ligand complexes derived from all the AH2 and B ligands decompose to produce either the fully deprotonated binary complexes, Cu(H 1A)- or the ternary hydroxo complexes Cu(H 1A)(OH)2 depending upon the nature of the B-ligands