The synthesis, crystal structure and thermal properties of an energetic compound: the hydrated azanium salt of 3,6-bis[(1H-1,2,3,4-tetrazol-5-yl)amino]-1,2,4,5-tetrazine

Abstract

The energetic ionic salt bis(1-aminoguanidin-2-ium) 5,5'-[1,2,4,5-tetrazine-3,6-diylbis(azanediyl)]bis(1H-1,2,3,4-tetrazol-1-ide) dihydrate, 2CH₇N₄⁺·C₄H₂N₁₄^2-·2H₂O, (I), with a high nitrogen content, has been synthesized and examined by elemental analysis, Fourier transform IR spectrometry, ¹H NMR spectroscopy and single-crystal X-ray crystallography. Compound (I) crystallizes in the monoclinic space group P2₁/c with two water molecules. However, the water molecules are disordered about an inversion centre and were modelled as half-occupancy molecules in the structure. The crystal structure reveals a three-dimensional network of molecules linked through N-H...N, N-H...O, O-H...N and O-H...O hydrogen bonds. Thermal decomposition was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The exothermic peak temperature is 509.72 K, which indicates that hydrated salt (I) exhibits good thermal stability. Non-isothermal reaction kinetic parameters were calculated via both the Kissinger and the Ozawa methods to yield activation energies of E_k = 239.07 kJ mol^-1, lgA_k = 22.79 s^-1 and E_O = 235.38 kJ mol^-1 for (I). Additionally, the thermal safety was evaluated by calculating critical temperatures and thermodynamic values, viz. T_SADT, T_TIT, T_b, ΔS^≠, ΔH^≠ and ΔG^≠. The results reveal that (I) exhibits good thermal safety compared to other ion salts of 3,6-bis[(1H-1,2,3,4-tetrazol-5-yl)amino]-1,2,4,5-tetrazine (BTATz).

Keywords: 1,2,3,4-tetrazole; 1,2,4,5-tetrazine; DSC; TGA; crystal structure; energetic ionic salt; high nitrogen content; hydrogen-bonding interactions; thermal properties.