Pressure-induced phase transition of 3,4-dinitropyrazole by 2D hydrogen bonded networks

As a kind of energetic material, explosives would face an environment of high-pressure during initiation to detonation or under shock waves. Under such conditions, explosives would experience a phase transition and even directly decompose. Therefore, there is a need to achieve the high-pressure evolution of explosives. 3,4-dinitropyrazole (DNP), which has excellent energy and sensibility, can be used as a potential carrier of melt cast explosive to replace TNT. However, the structural evolution of DNP with the increase in pressure remains elusive. With the help of diamond anvil cell technology, in situ high-pressure angle-dispersive x-ray diffraction (ADXRD) and Raman spectra were performed to investigate the structural variations of DNP. Both ADXRD and Raman experiments indicated that the DNP experienced a phase transition in the pressure range between 6.1 and 9.2 GPa. After carefully analyzing the Hirshfeld surface, first-principles calculations, and Raman spectra, we suggested that the newly generated N-H⋯N hydrogen bonds should be responsible for these high-pressure changes. The DNP crystal packing patterns have been changed from 1D molecular tapes to 2D hydrogen bonded networks. This research systemically investigated the high-pressure structural changes of DNP and studied the evolution of weak intermolecular interactions, so it built the relationship between phase transition and weak intermolecular interactions.