Comparative Study of the Formation of Heterometallic Diethylenetriaminpentaacetates of Cobalt(II), Nickel(II), and Copper(II) in Aqueous Solutions

The formation of heterobinuclear complexes of cobalt(II), nickel(II), and copper(II) with diethylenetriaminepentaacetic acid (dtpa, H(5)dtpa) in aqueous solutions was studied by spectrophotometry. The effect the pH has on the formation of the coordination sphere of heterobimetallic complex particles in ternary systems with an equimolar ratio of components is established. The thermodynamic stability of homo- and heterobinuclear complexes is estimated via mathematical modeling of the formation of complex particles of a certain stoichiometry with limited logarithmic processing of experimental data for specific polycomponent systems. Numerical values of logarithms of the constant of stability (log beta) of homobinuclear chelates [Me(2)dtpa](-) are 24.46 +/- 0.1; 25.53 +/- 0.1 and 27.03 +/- 0.1 for Co(II), Ni(II), and Cu(II), respectively. Values log beta are 25.43 +/- 0.1; 25.60 +/- 0.1; 17.83 +/- 0.09; and 27.57 +/- 0.1 for heterobimetallic diethylenetriaminepentaacetates [CoNidtpa](-), [CoCudtpa](-), [NiCuHdtpa](0), and [NiCudtpa](-), respectively.