Potentiometric determination of the formation constants for complexes of 3,2′,2"-triaminopropyldiethylamine with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II)

The tripodal tetraamine ligand N{(CH2)(3)NH2}{(CH2)(2)NH2}(2) (pee), has been investigated as an asymmetrical tetraamine chelating agent for Co-II, Ni-II, Cu-II, Zn-II and Cd-II. The protonation constants for this ligand and the formation constants for its complexes have been determined potentiometrically in 0.1 M KCl at 25 degreesC. The successive protonation constants (log K-n) are: 10.22, 9.51, 8.78 and 1.60 (n = 1-4). One complex with formula M(pee)(2+) (M = Co, Ni, Cu, Zn and Cd) is common to all five metal ions and the formation constant (log beta(ML)) is: 12.15, 14.17, 16.55, 13.35 or 9.74, respectively. In addition to the simple complexes, Co-II, Cu-II and Zn-II also give hydroxo complexes, and Cu-II and Ni-II give complexes with monoprotonated pee. [Zn(pee)](ClO4)(2) and [Cd(pee)Cl](ClO4) complexes were isolated and are believed to have tetrahedral and trigonal-bipyramidal structures, respectively.