Ring size effect on the enthalpies of formation of copper(II) and zinc(II) complexes with 1,4,7,10-tetraazacyclododecane and 1,5,9,12-tetraazacyclopentadecane

The heats of formation, ΔH, of the title complexes were detd. calorimetrically in aq. solns. at 25°. Comparison with ΔH values for the Cu complexes obtained by temp.-dependent stability const. studies (M. Kodama and E. Kimura, 1975 and 1976) and with ΔH calorimetric data for Cu complex with 1,4,8,11-tetraazacyclotetradecane (authors, to be published), allows to evaluate the 2 methods of obtaining ΔH values and to consider the effect of the ring size on ΔH. The mol. structure of the complexes is discussed.