Thermodynamics of complex formation with linear aliphatic tetra-amines. Part III. Enthalpy and entropy contributions to the stability of metal complexes of 4,7-diazadecane-1,10-diamine

Abstract

The enthalpies of the reactions, in 0·5M-KNO₃ at 25 °C, between the lineartetra-amine 4,7-diazadecane-1,10-diamine (3,2,3-tet) and the hydrogen, copper(II), nickel(II), and zinc(II) ions have been determined by means of direct calorimetric titrations. By use of the ΔG values reported elsewhere the corresponding ΔS values have been calculated. Complexes of 3,2,3-tet, which contains a system of condensed chelate rings with the ring-size sequence 6,5,6, have heats of formation higher than those of the corresponding complexes of 2,2,2-tet (ring-size sequence 5,5,5) and of 3,3,3-tet (sequence 6,6,6). However copper(II) and zinc(II) complexes have a less negative ΔH than the complexes of 2,3,2-tet which has the ring-size sequence 5,6,5.