Potentiometric examination of ternary complexes of 2,4-D and 2,4-MCPA, components of a weedkiller, with Cu2+, Cd2+, Hg2+, Pb2+ and Zn2+, and a quantum approach to their structures.

The study of the ternary interactions of some phenoxyacetic acids derived from a herbicide, with the heavy metals present in soil in trace amounts has been realized by potentiometric measurements. The stability constants of the ternary complexes have been calculated at 25°C and ionic strength 0.1(NaNO₃). The experimental results have confirmed the presence of one ternary hydroxide species MH₁(2,4-D)(2,4-MCPA) for Cu(II), Pb(II) and Zn(III) on one hand and MH₂(2,4-D)(2,4-MCPA) for Hg(II) on the other. The order of stability constants has been found to be: Cu(II)> Hg(II)> Pb(II)> Zn(II)>Cd(II). Finally, a quantum approach has been achieved by the semi-empirical AM1 method for the mercuric complex. [ABSTRACT FROM AUTHOR]