Standard Enthalpy of Formation, Thermal Behavior, and Specific Heat Capacity of 2HNIW·HMX Co-crystals

2HNIW·HMX co-crystals are crystals composed of HNIW (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazisowurtzitane) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane), and the HNIW molecule and HMX molecule are combined with noncovalent bonds in a lattice at a 2:1 ratio. The 2HNIW·HMX co-crystals are successfully synthesized by Bolton’s method and characterized by powder X-ray diffraction, laser Raman spectrometer, differential scanning calorimeter (DSC), and high performance liquid chromatograph. The standard enthalpy of formation of 2HNIW·HMX co-crystals is obtained as 861.9 ± 18.6 kJ·mol–1 under the direction of a designed thermochemical cycle with a Calvet microcalorimeter. The thermal decomposition behavior of 2HNIW·HMX co-crystals was studied under the non-isothermal condition with DSC. The apparent activation energy (E) of the decomposition is 332.23 kJ·mol–1 by Kissinger method, 324.10 kJ·mol–1 by Ozawa method, 314.06 ± 4.26 kJ·mol–1 by Friedman–Reich–Levi method, and 306.81 ± 3.12 kJ·mol–1 by NL-INT-SY3 method, respectively. The pre-exponential factor (logA/s–1) is 29.33 ± 0.33 via compensation effect. A continuous Cp mode of Micro-DSC III was used to determine the specific heat capacity (Cp,m) of the target co-crystals from 283.15 to 333.15 K, and the Cp,m is 1114.04 ± 10.92 J·mol–1·K–1 at 298.15 K. These results could provide valuable information on 2HNIW·HMX co-crystals for both theory and application.