Chelating properties of linear aliphatic tetraamines with some bivalent transition metal ions. 1,5,8,12-Tetraazadodecane (3,2,3-tet)

The basicity consts. of 1,5,8,12-tetraazadodecane (3,2,3-tet) were detd. potentiometrically in 0.5 M KNO3 at 25°. The equil. between 3,2,3-tet and Ni2+, Cu2+, and Zn ions were investigated under similar conditions. The basicity consts. of 3,2,3-tet are compared with those of other tetraamines. The order is related to the inductive effect of the constituent groups in the mol. Two complexes were found with both Ni(II) and Cu(II): the 1:1 complex [ML]2+ and a protonated species [MHL]3+. In addn. to these 2 complexes, Zn formed the hydroxo complex [ZnLOH]+ at high pH. It is shown that an alternating sequence of 5- and 6-membered rings increases complex stability.