High Pressure Study of Pharmaceutical and Energetic Material Hexamethylenetetramine

This study presents the results of high-pressure Raman and angle-dispersive X-ray diffraction (ADXRD) investigations conducted on hexamethylenetetramine (HMT, (CH2)6N4), a hydrogen-bonded pharmaceutical and energetic material, across a range of pressures up to approximately 20 GPa. Notably, two distinct phase transitions at around 1.1 GPa and within the pressure interval of approximately 10 to 12.5 GPa were identified. Both Raman spectroscopy and ADXRD results substantiate the existence of these two phase transitions. The crystal structure of phase II could be indexed and refined as a tetragonal system with the P4/n space group, while phase III exhibits a tetragonal crystal system with the P41 space group. Furthermore, it is noteworthy that the observed transitions are fully reversible upon complete pressure release. Drawing upon the variations observed in the CNC, CN, and CH2 Raman modes within the high-pressure phases, we posit that the two phase transitions arise from the rearrangements within the hydrogen-bonded networks.