Calorimetric determination of macrocyclic enthalpy. Copper(II) and zinc(II) complexes with 1,4,8,11-tetra-azacyclotetradecane

The first direct calorimetric values for the enthalpies of formation of macrocyclic complexes in aqueous solution show for the title systems the existence of a macrocyclic enthalpy (CuII 4·7 and ZnII 3 kcal mol–1); for the CuII complex the enthalpy of formation fits the linear correlation with spectral energy as previously described for noncyclic nitrogen ligands.