Polynuclear complexes of the edta analogues

Complex formation by O,O'-bis-(beta-aminoethyl)-ethyleneglycol-N,N,N',N',-t etraacetate (egta) with Ni2+ and Zn2+ and of 1,5-diaminopentane-N,N,N',N'-t etraacetate (peta) with Ni2+ was investigated at 20 degrees C and l=1.00 (K NO3) using alkalimetric titrations of equimolar solutions of the components in the range 0.5-32 mM. While Zn2+ forms only mononuclear species, Ni2+ gi ves mono-, NiL2-, and polynuclear NiqHLq(q-1)- (q = 1, 2, 3, 4, 5, 6) compl exes. Complex formation by Hg2+ with edta and its homologues was investigat ed by emf measurements (glass and Hg electrode) under the same conditions. The total concentrations of mercury(II) was varied from 0.01 to 50 mM, usin g a metal-ligand ratios of 1 : 2. Only species with the same q value, of th e type HgqLq2q-, were present in these solutions, in the pH range 5-8, irre spective of the total concentrations of the components. The value of q is o ne for edta and two for the other ligands. The stability constants increase as the number of methylene groups between N atoms increases from 3 to 5. T he concentration stability constants of all the species formed are reported . (C) 1999 Elsevier Science B.V. All rights reserved.