1,2,4-Triazolium and Tetrazolium Picrate Salts: On the Way from Nitroaromatic to Azole-Based Energetic Materials

A family of energetic salts based on the picrate anion and several azolium cations were synthesized either by new methods or by known literature procedures. The cations of choice were the following: 5-amino-1H-tetrazolium (1), 5-amino-1-methyl-1H-tetrazolium (2), 5-amino-2-methyl-1H-tetrazolium (3), 5-amino-1,4-dimethyl-1H-tetrazolium (4), 5-amino-1,3-dimethyl-1H-tetrazolium (5), 1,5-diamino-1H-tetrazolium (6), 1,5-diamino-4-methyl-1H-tetrazolium (7), 3,4,5-triamino-1,2,4-triazolium or guanazinium (8) and 3,4,5-triamino-1-methyl-1,2,4-triazolium or methylguanazinium (9). A summary of the N-15 NMR shifts for all Compounds is given, and the proton-/methyl-induced shifts (PISs/MISs) are discussed with relation to the crystal structures. Because hydrogen bonding plays an important role in determining the density and thus the performance of energetic materials, the crystal structures are discussed in detail. In addition, tests to assess the impact (i) and friction (f) sensitivities of the compounds and thermal stability measurements (DSC) were also carried out, revealing insensitive compounds (i > 40 J, f > 360 N) with high thermal stabilities (T-d >175 degrees C). The constant volume energies of combustion were determined experimentally by oxygen bomb calorimetry and their validity was checked by quantum chemical calculation (MP2) of electronic energies. The detonation pressures and velocities of 1 (7795 ms(-1), 25.6 GPa), 2 (7343 ms(-1), 21.2 GPa), 3 (7213 ms(-1), 20.4 GPa), 4 (6876 ms(-1), 17.8 GPa), 5 (6846 ms(-1), 17.6 GPa), 6 (7864 ms(-1), 25.4 GPa), 7 (7492 ms(-1), 22.1 GPa), 8 (7495 ms(-1), 22.5 GPa) and 9 (7162 ms(-1), 19.8 GPa) were predicted by use of the EXPLO5 code. Lastly, the ICT code was used to predict the decomposition gases of all salts. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)