Thermodynamic behavior of complexes with 5,6-membered condensed chelate rings. 1,4,8-Triazaoctane

The enthalpies of the reactions between NH2(CH2)2NH(CH2)3NH2 and Ni2+, Cu2+, and Zn2+ in 0.5M KNO3 at 25° were detd. by direct calorimetric titrations and previously reported free energy values were used to calc. the corresponding entropy values. Complexes formed contained a system of condensed 5- and 6-membered chelate rings and had higher heats of formation than corresponding complexes of NH2(CH2)2NH(CH2)2NH2 (5,5-ring size sequence) and NH2(CH2)3NH(CH2)3NH2 (6,6-ring size sequence.). Addn. of a 2nd mol. of ligand to the complex depended on steric factors.