Electrostatic Potential Surface Properties Research Articles

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

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.

Towards low-impact-sensitivity through crystal engineering: New energetic co-crystals formed between Picric acid, Trinitrotoluene and 9-Vinylanthracene

New 1:1 energetic co-crystals formed between Picric acid, Trinitrotoluene and 9-Vinylanthracene were prepared by a solvent evaporation method. The structures of the co-crystals were determined and characterized via single-crystal and powder X-ray diffraction techniques, infrared spectroscopy and thermal analysis (DSC, TG). X-ray diffraction results show that the co-crystals are mainly formed through host-guest π ... π stacking with aid of intermolecular hydrogen bonding (C–H⋯N, C–H⋯O). Hirshfeld surfaces and associated fingerprint plots of the co-crystals were examined and the results indicated that the structures are stabilized by H ⋯ H (30.1% and 33.3%), O ⋯ H (24.3% and 19.5%), O ⋯ O (4.6% and 1.8%), C ⋯ H (3.8% and 5.3%) and C ⋯ C (6.8% and 6.8%) intermolecular interactions for PIC: VANT and TNT: VANT respectively. The use of Hirshfeld surfaces in combination with fingerprint plots demonstrates that these weak interactions are important for both local packing and crystal packing. The enthalpies of formation, the optimized structures, molecular total energies, frontier orbit energies, and HOMO-LUMO gaps of each compound were calculated using Gaussian 09; and detonation performances were calculated using the EXPLO5 software package. The co-crystals were found to be less impact-sensitive than Trinitrotoluene and Picric acid. This dramatic difference in co-crystal sensitivities may stem from the significantly different π-stacking, hydrogen bonding interactions, crystal packing, O ⋯ O interactions, HOMO-LUMO gaps, free space in crystal lattice, and the electrostatic potential surface properties seen in both co-crystal structures. These results highlight an important consideration in the design of future Trinitrotoluene and Picric acid energetic co-crystals, and the feasibility of improving sensitivity properties through co-crystallisation.