A new crystal form of Hx2TNBI·2H2O through solvent-induced crystallization

Polymorphism is universal in energetic materials (EMs), which is originated from the differences of molecular conformers and stacking mode. The polymorphic transition may lead to the change of crystal structure and properties of EMs. In this work, β-Hx₂TNBI·2H₂O (β-1) was successfully synthesized through solvent-induced conformational transition of Hx₂TNBI·2H₂O. From the perspective of quantum chemistry and molecular dynamics, the crystal stacking changes caused by different molecular conformations are discussed in detail, which leads to the properties difference of EMs. The results show that β-1 featured wave-like crystal stacking, making it less sensitive to external mechanical stimuli than α-Hx₂TNBI·2H₂O (α-1) (α-1: IS > 6 J, FS > 288 N; β-1: IS > 20 J, FS > 360 N). α-1 featured better the aromaticity, which gives it higher thermal stability than β-1 (α-1: T_d = 186 °C; β-1: T_d = 146 °C). Simultaneously, compared with β-1, α-1 has higher crystal density and detonation performance. This work provides a new and effective way to change the safety of EMs.