Microcalorimetric determination of the enthalpy of a slow reaction: destruction with cyanide of the macrocyclic(1,4,8,11-tetraazacyclotetradecane)nickel(II) ion

The calorimetric detn. of the enthalpy of formation of (1,4,8,11-tetraazacyclotetradecane)nickel was made by displacing the macrocyclic ligand with cyanide and following the reaction to completion (5 h) in a batch microcalorimeter of the heat-flow type. The ΔH° value found (-20.3 kcal mol-1) is 11 kcal mol-1 less than that previously reported. Thermodn. parameters of both octahedral and square-planar forms of the complex were calcd. The macrocyclic effect in Ni(II) complexes was rationalized with that already established for Cu(II) complexes.