Derivatives of 1,5-Diamino-1H-tetrazole:  A New Family of Energetic Heterocyclic-Based Salts

1,5-Diamino-1H-tetrazole (2, DAT) can easily be protonated by reaction with strong mineral acids, yielding the poorly investigated 1,5-diaminotetrazolium nitrate (2a) and perchlorate (2b). A new synthesis for 2 is introduced that avoids lead azide as a hazardous byproduct. The reaction of 1,5-diamino-1H-tetrazole with iodomethane (7a) followed by the metathesis of the iodide (7a) with silver nitrate (7b), silver dinitramide (7c), or silver azide (7d) leads to a new family of heterocyclic-based salts. In all cases, stable salts were obtained and fully characterized by vibrational (IR, Raman) spectroscopy, multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, X-ray structure determination, and initial safety testing (impact and friction sensitivity). Most of the salts exhibit good thermal stabilities, and both the perchlorate (2b) and the dinitramide (7c) have melting points well below 100 °C, yet high decomposition onsets, defining them as new (7c), highly energetic ionic liquids. Preliminary sensitivity testing of the crystalline compounds indicates rather low impact sensitivities for all compounds, the highest being that of the perchlorate (2b) and the dinitramide (7c) with a value of 7 J. In contrast, the friction sensitivities of the perchlorate (2b, 60 N) and the dinitramide (7c, 24 N) are relatively high. The enthalpies of combustion (Δ_cH°) of 7b−d were determined experimentally using oxygen bomb calorimetry: Δ_cH° (7b) = −2456 cal g^-1, Δ_cH° (7c) = −2135 cal g^-1, and Δ_cH° (7d) = −3594 cal g^-1. The standard enthalpies of formation (Δ_fH°) of 7b−d were obtained on the basis of quantum chemical computations using the G2 (G3) method:  Δ_fH° (7b) = 41.7 (41.2) kcal mol^-1, Δ_fH° (7c) = 92.1 (91.1) kcal mol^-1, and Δ_fH° (7d) = 161.6 (161.5) kcal mol^-1. The detonation velocities (D) and detonation pressures (P) of 2b and 7b−d were calculated using the empirical equations of Kamlet and Jacobs:  D(2b) = 8383 m s^-1, P(2b) = 32.2 GPa; D(7b) = 7682 m s^-1, P(7b) = 23.4 GPa; D(7c) = 8827 m s^-1, P(7c) = 33.6 GPa; and D(7d) = 7405 m s^-1, P(7d) = 20.8 GPa. For all compounds, a structure determination by single-crystal X-ray diffraction was performed. 2a and 2b crystallize in the monoclinic space groups C2/c and P2₁/n, respectively. The salts of 7 crystallize in the orthorhombic space groups Pna2₁ (7a, 7d) and Fdd2 (7b). The hydrogen-bonded ring motifs are discussed in the formalism of graph-set analysis of hydrogen-bond patterns and compared in the case of 2a, 2b, and 7b.