Highly energetic N-cyano-substituted CL-20 analogues: challenging the stability limits of polynitro hexaazaisowurtzitanes

Abstract

To design high-energy-density materials of a new level, it is necessary to develop methods for the functionalization of energetic scaffolds, which will make it possible to tune their physicochemical and energetic properties. For this reason, we have elaborated an approach for synthesizing a new series of energetic cage compounds with advanced properties by introducing the N-cyano group into the polynitro hexaazaisowurtzitane framework. The structures of the obtained substances were fully characterized with a combination of methods, including multinuclear (¹H, ¹³C{¹H}, ¹⁴N, and ¹⁵N{¹H}) NMR and IR spectroscopy, high-resolution mass spectrometry, X-ray diffraction analysis, electron microscopy and quantum chemical calculations. For the resulting compounds, thermal stability and safety tests were carried out, calorimetric and pycnometric measurements were performed, and the energetic potential was determined by high-temperature chemical equilibrium thermodynamic calculations. The new cyano derivatives have an acceptable density (up to 1.92 g cm⁻³) and a high enthalpy of formation (up to 2 MJ kg⁻¹), which is 2 times that of the benchmark CL-20. The resistance of the target compounds to friction (up to 220 N) is the highest compared to CL-20 and its known analogues. 4,10-Dicyano-2,6,8,12-tetranitro-2,4,6,8,10,12-hexaazaisowurtzitane of the new series is the most thermally stable (a T_dec of 238 °C) among the known energetic polynitro hexaazaisowurtzitanes and is the first derivative of this family to surpass CL-20 in heat resistance. Moreover, the specific impulse for the novel materials showed an improvement of 6.5–13 s over CL-20.