High-Pressure Structural Response of an Insensitive Energetic Crystal: 1,1-Diamino-2,2-dinitroethene (FOX-7)

Abstract

High-pressure structural response of an insensitive energetic crystal—1,1-diamino-2,2-dinitroethene (FOX-7)—was examined to gain insight into its structural and chemical stability and to obtain isothermal compression data. Using synchrotron single-crystal X-ray diffraction measurements, details of pressure-induced structural changes to 12.8 GPa were determined across three FOX-7 phases: α (P21/n), α′ (P21/n), and e (P1). We found that the C–NO2 bond is the most compressible chemical bond, and high pressure significantly reduces and homogenizes the length of H bonds in the hydrogen-bond network. The α′−e phase transition, at 4.5 GPa, significantly affects all molecular and crystal properties, whereas the α–α′ transition, at 2 GPa, is associated with subtle molecular and intermolecular changes. Anisotropic compressibility was observed over the entire pressure range, consistent with the layered structure of the crystal. The equation-of-state parameters were obtained using the third-order Birch–Murnaghan equa...