Dimer Species in Aqueous Solutions of 2,6-Toluenediamine-N,N,N′,N′-Tetraacetic Acid with Copper(II), Nickel(II), Cobalt(II) and Zinc(II)

The complex species formed in aqueous solution between 2,6-toluenediamine-N,N,N′,N′-tetraacetic acid (2,6-TDTA) and Cu(II), Ni(II), Co(II), Zn(II), Cd(II) and Mn(II), respectively, were studied at 25[ddot]C and ionic strength 0.1 M in KCI. The application of the least-squares computer program SUPERQUAD to the experimental potentiometric data indicates that, upon varying the ligand: metal relationships and concentrations, the following complex species are formed (ligand, H4L): Cu(II) (CuH2L, [CuHL]−, [CuL]2−, [Cu2H2L]2 +, Cu2L, [Cu2HL2]3− and [Cu2L2]4−); Ni(II) (NiH2L, [NiHL]−, [NiL]2−, [Ni2HL] +, [Ni2HL2]3- and [Ni2L2]4−); Co(II) ([CoHL]−, [CoL]2−, [Co2H2L]2 +. [Co2HL] +, [Co2HL2]3− and [Co2L2]4−); Zn(II) (ZnH2L, [ZnHL]−, [ZnL]2−, [Zn2H2L]2 +, [Zn2HL2]3− and [Zn2L2]4−); Cd(II) (CdH2L, [CdHL]−, [CdL]2− and [CdHL2]5−; and Mn(II) (MnH2L, [MnHL]− and [MnL]2−). The dimer species [M2L2)4− has been identified for the first time in potentiometric studies in aqueous solution. Compared with m-PDTA acid, th...