Standard enthalpy of formation of a CL-20 bimolecular crystal with tris-oxadiazol-azepin and its thermal stability

The standard enthalpies of combustion and formation of 7$H$-tris([1,2,5]oxadiazol)[3,4-b:3',4'-d:3',4'-f]azepin, its bimolecular crystal with the $\gamma$-polymorph (CL-20), and $\gamma$-polymorphs of CL-20 are experimentally determined. The standard enthalpies of formation of the bimolecular crystal and the equimolecular mechanical mixture of $\gamma$-CL-20 with azepin are found to differ by less than 12.8 kJ/mol. This small difference is validated by quantum-chemical calculations. It is experimentally observed that the presence of azepin in the bimolecular crystal inhibits thermal decomposition of $\gamma$-CL-20 and increases the thermal stability of $\gamma$-CL-20 in the bimolecular crystal as compared to $\gamma$-CL-20 in the initial state.