Intriguing rotational conformations of energetic 1,2,4-triazole-pyrazoles: comparative insights into versatile N-functionalization and structure-property modulation

Various N-site functionalizations of nitrogen-rich heterocycles enable considerable structural diversity in high-energy molecules. However, the rotational conformations of polycyclic backbones have been largely overlooked, thereby limiting a thorough understanding of their structure-property relationships. In this contribution, three polynitro-functionalized energetic analogues were achieved by N-functionalization of the 1,2,4-triazole-pyrazole-based precursor (1). With incorporating nine nitro groups, 5-(4,5-dinitro-1-(trinitromethyl)-1H-pyrazol-3-yl)-3-nitro-1-(trinitromethyl)-1H-1,2,4-triazole (7) features a positive oxygen balance (CO₂ = +11.3%) and high positive heat of formation (ΔH_f = +660.9 kJ mol⁻¹). 5-(3,4-Dinitro-1-(trinitromethyl)-1H-pyrazol-5-yl)-1-(dinitromethyl)-3-nitro-1H-1,2,4-triazole (5) has the highest density (d = 1.933 g cm⁻³) and detonation properties (P = 37.2 GPa, V_D = 9160 m s⁻¹) among these three compounds. The comparative results of single-crystal X-ray diffraction indicate that N-functionalized groups of 5 are substituted on opposite sides, whereas the N-functional groups of the other two energetic compounds (6 and 7) are substituted on the same side. Further structural analysis reveals that the distinct energetic performance not only originates from diverse functionalization, but is also impacted by the rotational conformation of the triazole-pyrazole skeleton.