Investigating the Stabilizing Forces of Pentazolate Salts

Abstract

Pentazolate (cyclo-N 5 − ) salts are actively pursued energetic nitrogen-rich compounds due to their potential as propellants and explosives. An in-depth understanding of the stabilizing forces between cyclo-N 5 − anions and cations is important for designing cyclo-N 5 − salts and achieving cyclo-N 5 − salt conversions. Herein, the metathetical syntheses of cyclo-N 5 − salts (compounds 1− 4) containing heterocyclic amino-based cations 3,6-diguanidino-1,2,4,5-tetrazine, and 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazol-2-ium are reported. In addition, an energetic cocrystal (compound 5) composed of compound 4 with 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazole was synthesized using cocrystallization techniques. Crystal structures were investigated through geometrical and Hirshfeld analyses and theoretical calculations to reveal the contributions of hydrogen-bonding and π-stacking interactions in stabilizing the pentazolate salts. Compounds 1−3 are stabilized by strong hydrogen-bonding interactions and weak π-stacking interactions. The π-stacking interactions (cation−anion π + −π − contacts) are stronger in 4 and have an important role in promoting the stability of the salt. The binding energy of this π-stacking interaction (−82.4 kcal mol −1 ) slightly surpasses that of the robust N6-H6A•••N1 interaction (−75.1 kcal mol −1 ). For cocrystal 5, the spatial arrangement of its structural framework differs from that of its precursor, compound 4. The molecular stabilization energy, which increases from −75.1 to −94.3 kcal mol −1 during the conversion of 4−5, primarily arises from strong π-stacking interactions. Further observations indicate that cocrystal 5 has better thermal stability and detonation performance than 4, which establishes noncovalent modification via cocrystallization as an efficient method for forming multicomponent crystal systems and highlights the ability of coformers to modify energetic performance.

Effect of Hydrogen Bond Interaction on the Decomposition Temperature, Aromaticity, and Bond Order of Nonmetallic Pentazolate Salts

“…Specifically, salts 1a and 1b of group 1 only have N and H atoms. Salts in group 2 − and group 3 − have C, N, and H atoms, and the difference is that group 2 comprises guanidyl while group 3 contains triazolyl. Salts 4a – 4g of group 4 − possess C, N, H, and O atoms without crystal water.…”

Anion–Cation Bonding and Structure–Property Relationships of Three cyclo-Pentazolate Compounds

“…Polynitrogen materials have attracted substantial interest in materials science because of their promising applications in modern military and aerospace fields. − As a representative polynitrogen compound, the five-membered pentazolate anion, c -N 5 – , which was not synthesized and isolated in bulk until 2017, has become an attractive scaffold for the design and synthesis of energetic materials and inorganic ferrocene analogues. − Currently, the development of nonmetallic pentazolate salts is receiving increased attention in the field of pentazole chemistry because of the prospects of such salts to be promising explosives.…”

Amphoteric Ionization and Cocrystallization Synergistically Applied to Two Melamine-Based N-Oxides: Achieving Regulation for the Comprehensive Performance of Energetic Materials

“…18−26 Energetic cocrystals can alter the solubility and hygroscopicity of their components and can possess better thermal and mechanical stability in comparison to their more energetic pure components. 25,27,28 A defect of most energetic cocrystals is that the detonation performance of the high-energetic components is dragged down by the lessenergetic or nonenergetic coformers. 25,29 compounds with positive and negative oxygen balances (OBs), respectively, may have higher detonation performance in comparison to their components (Figure 1).…”

“…Cocrystallizing energetic compounds with heterogeneous solid components to form cocrystals has been an emerging method of improving the performance of energetic materials in the past 10 years. − Energetic cocrystals can alter the solubility and hygroscopicity of their components and can possess better thermal and mechanical stability in comparison to their more energetic pure components. ,, A defect of most energetic cocrystals is that the detonation performance of the high-energetic components is dragged down by the less-energetic or nonenergetic coformers. , Recently Bennion and Matzger proposed that cocrystals composed of energetic compounds with positive and negative oxygen balances (OBs), respectively, may have higher detonation performance in comparison to their components (Figure ). However, to date existing energetic cocrystals whose composition fits the above description are very scarce, ,, and only one of them (composed of ammonium dinitramide and pyrazine 1,4-dioxide) achieved the detonation performance improvement noted above.…”