Enthalpy of formation of CL-20

The gas-phase enthalpy of formation of CL-20 was predicted within the range of 500–550 kJ/mol on the basis of isodesmic reaction calculations using the G4(MP2) and B3LYP/cc-pVTZ levels of theory. These values combined with the most probable values of enthalpy of sublimation, 150–170 kJ/mol, suggest the values in the range between 330 and 400 kJ/mol for the enthalpy of formation of solid CL-20, in agreement with the reported experimental value of 377.4 ± 13 kJ/mol when the combined errors of experimental and theoretical determinations are taken into account. Thus, our calculations do not support a substantially larger value of ∼550 kJ/mol for the enthalpy of formation of solid CL-20 suggested recently from several quantum chemical calculations.