Thermodynamic behaviour of complexes with 5,6-membered condensed chelate rings: 1,4,8-triazaoctane

Abstract

The enthalpies of the reactions. in 0·5M-KNO3 at 25 °C, between the linear tri-amine 1,4,8-triazaoctane (2,3-tri) and nickel(II), copper(II), and zinc(II) ions have been determined by means of direct calorimetric titrations. By using the ΔG° values reported elsewhere the corresponding ΔS° values have been calculated. The ML complexes of (2,3-tri) which contain a system of condensed chelate rings with a 5,6-ring size sequence, have heats of formation higher than those of the corresponding complexes of (2,2-tri)(5,5-ring size sequence) and of (3,3-tri)(6,6-sequence). An analogous trend has already been observed in tetra-amine complexes. The importance of steric factors in the formation of the ML2 complexes is discussed.