The binding ability of cadmium(II), lead(II), and zinc(II) with N,N'-(S,S)bis[1-carboxy-2-(imidazol-4yl)ethyl]ethylenediamine (BCIEE) and the structure of the formed complexes have been investigated, in aqueous solution, by potentiometry and (1)H NMR and (13)C NMR spectroscopy for the first time. Stability constants for the cadmium, lead, and zinc complexes with BCIEE were studied by glass electrode potentiometry (GEP) at a fixed total ligand to total metal concentration ratios, varied pH values at (25.0 +/- 0.1) degrees C, and an ionic strength of 0.1 M KCl. For the Cd-BCTEE and Pb-BCTEE systems, three species, MH(2)L, MHL, and ML, were identified. For the Cd-BCIEE system, the overall stability constants values are 20.63 +/- 0.02, 14.78 +/- 0.01, and 8.22 +/- 0.02, respectively. For the Pb-BCIEE system, the overall stability constants values are 19.71 +/- 0.02, 13.78 +/- 0.02, and 6.63 +/- 0.02, respectively. For the Zn-BCIEE system, two species, ZnH(2)L and ZnL, were identified, and the overall stability constants values are 21.84 +/- 0.03 and 10.77 +/- 0.04, respectively. In addition, the combined analysis of (1)H NMR and (13)C NMR spectroscopic data enabled the establishment of the coordination modes of the metal complexes between BCIEE and the Cd(II) or Zn(II) metal ions.