Metal complexes of some peptide derivatives. Part-XV. Mixed ligand complex formation of copper(ll) with some N-benzenesulfonyldipeptides as primary ligands and acetate, 2-methylbenzimidazole, glycinate and bipyridine as Secondary ligands

Department of Chemistry, University of Calcutta, University College of Science, 92, A PC Road!

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Bengal Chemicals and Pharmaceutical Works, Kolkata-700 009, India

Manuscript received 24 November 2000

Potentiametric investigation on the coniplex foi matioh equilibria of Cu^ll 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