From van der Waals interactions to structures and properties of 3,[formula omitted]-dinitro-5,[formula omitted]-bis-1,2,4-triazole-1,[formula omitted]-diolate based energetic materials

Abstract

As a continuation for the search of precise correlation between performance and sensitivity of high energy density materials (Phys. Chem. Chem. Phys. 2018, 20, 29693), we present structure analysis and quantum mechanical calculations for similar energetic ionic salts (EIS) based on 3,3′-dinitro-5,5′-bis-1,2,4-triazole-1,1-diolate anion with ammonium (DA-DNBTO) and hydrazinium (DH-DNBTO) cations. The geometry optimization demonstrate the importance of van der Waals correction when studying the structure and properties of EIS, and highlights the significance of DFT-D2 method proposed by Grimme in reproducing the experimental crystal structures of energetic salts. The IR spectrum of DA-DNBTO contains more number of intense peaks in the high frequency range (above 2850 cm−1) compared to DH-DNBTO. Especially, the electronic band gap of DNBTO salts obtained using the HSE06 hybrid functional are reduced to 50% when compared with that of BTO based energetic salts due to NO2 group attached to the DNBTO anion. Besides, we find that the O...O contacts that generally exist in most of the energetic materials do not show much impact in both the studied energetic salts. The strong intermolecular interactions of DA-DNBTO represents its inferiority in molecular stability, which is in good agreement with the experimentally measured impact sensitivity (>40 J) and friction sensitivity (360 N) values and also explains why it has highest stability compared to DH-DNBTO. Our calculations re-verifies the importance of intermolecular hydrogen bonding in the construction of high performance and low sensitive energetic materials.