Crystal engineering with energetic picric acid halogen-based salts: Promising properties of a new family of insensitive materials

Abstract

Newly designed 1:1 energetic salts formed by pairing the picric acid with 3-chloroaniline, 4-chloroaniline, 3-bromoaniline, and 4-iodoaniline were achieved by the solvent evaporation method. The structures of the target salts were then determined and characterized according to single-crystal and powder X-ray diffraction techniques, infrared spectroscopy, and thermal analyses (DSC and TGA). Single-crystal X-ray diffraction results revealed that the salts are mainly formed through host-guest (anions-cations) with the aid of inter-molecular hydrogen bond (N–H … O, C–H … O) and halogen bond (C-Br… O, C-I… O). The enthalpies of formation, the optimized structures, total energies, and frontier orbital energies of each compound were calculated using Gaussian 09, whereas the detonation performances were calculated using the EXPLO5 software package. Using the BAM fall hammer instrument, it was determined that the salts were less impact sensitive than picric acid. This significant difference in impact sensitivities of salts may arise from considerably halogen-bonded and hydrogen-bonded interactions, packing coefficient, oxygen-oxygen (O…O) interactions, free space in the crystal lattice, and electrostatic potential surface properties. These findings might be exploited to build novel crystallization techniques based on energetic halogen compounds. Thus, the novel four energetic salts exhibit an appealing combination of high energy and low sensitivity and therefore may be exploited as a potential insensitive biocidal material option in the future in place of picric acid in low vulnerability formulations.