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

Potentiometric investigation on the complex formation equilibria of CuII with N-benzenesulfonyl derivatives of some dipeptides, viz. glycylglycine, glycyl-p-alanine and P-alanylglycine, hereafter, abbreviated as NBSGG, NBSGB and NBSBG (AH(2)) respectively, in the presence of typical secondary ligands, viz. acetate (ac-), 2-methylbenzimidazone (bz), glycinate (gly-) and bipyridine (bipy), hereafter, B, provides evidence of formation of varieties of binary and ternary complexes of the types : Cu(AH), Cu(H(-1)AH), Cu(H(-1)A), Cu(H(-1)A)(OH), Cu(B), Cu(B)(AH), Cu(B)(H(-1)AH) and Cu(B)(H(-1)A). Stability constants of the complexes at 25 V, 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. The sulfonamidodipeptide ligands (AH2) provide three coordinating groups : -COOH, -CONH-, and -SO2NH-, and show ambidentism in forming the binary and the ternary complexes depending upon the denticity, sigma-basicity and pi-acidity of the B-ligands. The ternary complexes are found to be stable in the intermediate pH range (5-8). Above pH 8, the mixed ligand complexes derived from all the AH(2) and B-ligands decompose to produce either the fully deprotonated binary complexes, Cu(H(-1)A)(-) or the ternary hydroxo complexes Cu(H(-1)A)(OH)(-2) depending upon the nature of the B-ligands.