Pressure-induced phase transition of a series of energetic pentazolate anion salts: a DFT study

The pressure-induced geometry and crystal structures, electronic features, hydrogen bonding networks, and vibrational properties of two energetic pentazolate anion salts (N₅⁻)₂DABTT₂⁺ and N₅⁻GU⁺ were investigated by density functional theory (DFT) calculations. The results show that a critical point of phase transition at 9 GPa for (N₅⁻)₂DABTT₂⁺ was found, while for N₅⁻GU⁺ it was not. The distortion of cations DABTT₂⁺ and GU⁺ was found to be positively correlated with the pressure, thereby affecting the hydrogen bond network distribution in the crystals. The discussions on electronic structures suggest that pressure can lead to an increase of charge overlap and delocalization, thereby improving the ability of electron transition. The topological analysis of the hydrogen bonds reveals that both hydrogen bonding interactions and the degree of contribution of a specific atom to the hydrogen bonding interactions gradually improve as the pressure increases, with a discontinuity at 9 GPa only for (N₅⁻)₂DABTT₂⁺. The vibrational properties of both crystals were discussed and the critical point of phase transition at 9 GPa was also found in (N₅⁻)₂DABTT₂⁺. Our findings provide a new perspective on the response mechanism of energetic pentazolate anion salts to high pressure, and are expected to provide meaningful guidance for the application of pentazole energetic materials.