TERNARY COMPLEXES OF 1,4-PHENYLENEDIAMINE-N,N-DISUCCINIC AND 2,5-TOLUENEDIAMINE-N,N-DISUCCINIC ACIDS WITH THE CATIONS CO(II), NI(II) AND ZN(II)

A potentiometric study of the formation equilibria involved in the nov el ternary systems M(II)-A-B, in an aqueous solution of 0.5 M NaCl at 25-degrees-C-where A is 1,4-phenylenediamine-N,N'-disuccinic acid (1,4 -FDDS) or 2,5-toluenediamine-N,N'-disuccinic acid (2,5-TDDS), B is oxa lic, malonic or succinic acid and M is Co, Ni or Zn-, has been carried out. The complexes MABH, MABH2 and MABH3 are detected in all the syst ems studied, the neutral complex MAB appearing only in the case of the systems M(II)-2,5-TDDS-oxalic acid. The parameters used to evaluate t he stability of the ternary complexes with respect to the binary ones were DELTAlog K, log X and Log beta(stat. From the values of these par ameters it is deduced that the stability of the ternary systems increa ses as the number of members of the chelate ring of the secondary liga nd increases.