High pressure structural behaviour of 5,5'-bitetrazole-1,1'-diolate based energetic materials: a comparative study from first principles calculations.

Pressure on the scale of gigapascals can cause incredible variations in the physicochemical and detonation characteristics of energetic materials. As a continuation of our earlier work (B. Moses Abraham, et al. , Phys. Chem. Chem. Phys. , 2018, 20 , 29693-29707), here we report the high pressure structural and vibrational properties of 5,5'-bitetrazole-1,1'-diolate based energetic ionic salts via dispersion-corrected density functional theory calculations. Remarkably, these energetic materials exhibit anisotropic behavior along three crystallographic directions with progressing pressure; especially, the maximum and minimum reduction in volume is observed for HA-BTO and TKX-50, respectively. The large bulk modulus of TKX-50 (28.64) indicates its hard nature when compared to other BTO-based energetic salts. The effect of pressure on hydrogen bonded D-H⋯A energetic materials induces spectral shift (lengthening/shortening) in the donor group (D-H) of the stretching vibrations and is widely recognized as the signature of hydrogen bonding. We observed unusual contraction of the D-H bond under compression due to the short range repulsive forces encountered by the H atom while the molecule attempts to stabilize. The Hirshfeld surface analysis highlights the pressure induced stabilization of HA-BTO due to increased N⋯H/H⋯N and O⋯H/H⋯O close contact of hydrogen bond acceptors and donors. These studies provide theoretical guidance as a function of pressure, on how the micro-structures and intermolecular interactions can tune macroscopic properties to enhance the energetic performance.