Investigating the Stabilizing Forces of Pentazolate Salts

Pentazolate (cyclo-N5–) 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-N5– anions and cations is important for designing cyclo-N5– salts and achieving cyclo-N5– salt conversions. Herein, the metathetical syntheses of cyclo-N5– salts (compounds 1–4) containing heterocyclic amino-based cations 3,6-diguanidino-1,2,4,5-tetrazine, 1-guanyl-1,2,4-triazolium, 3,7-diamino-7H-[1,2,4]­triazolo­[4,3-b]­[1,2,4]­triazol-2-ium, 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.五唑盐（cyclo-N5–）是一类备受关注的含能富氮化合物，因其可用作推进剂与炸药而具备重要应用价值。深入理解环五氮阴离子与阳离子之间的稳定作用力，对于环五氮阴离子盐的设计与转化制备具有重要意义。本文报道了四类含杂环氨基类阳离子的环五氮阴离子盐（化合物1~4）的复分解合成方法，所采用的阳离子分别为3,6-二胍基-1,2,4,5-四嗪、1-胍基-1,2,4-三唑鎓、3,7-二氨基-7H-[1,2,4]三唑并[4,3-b][1,2,4]三唑-2-鎓以及3,6,7-三氨基-7H-[1,2,4]三唑并[4,3-b][1,2,4]三唑-2-鎓。此外，本文采用共晶技术合成了由化合物4与3,6,7-三氨基-7H-[1,2,4]三唑并[4,3-b][1,2,4]三唑构成的含能共晶（化合物5）。通过几何分析、希尔施菲尔德分析（Hirshfeld）与理论计算对晶体结构进行表征，以揭示氢键与π堆积相互作用在稳定五唑盐过程中的贡献。化合物1~3主要通过强氢键相互作用与弱π堆积相互作用实现结构稳定。化合物4中的π堆积相互作用（阳离子-阴离子π+–π–接触）强度更高，对该盐的结构稳定性具有重要的促进作用。该π堆积相互作用的结合能为-82.4 kcal mol–1，略高于较强的N6-H6A···N1相互作用（-75.1 kcal mol–1）。对于共晶5而言，其结构骨架的空间排布与其前驱体化合物4存在显著差异。从化合物4转化为共晶5的过程中，分子稳定化能从-75.1 kcal mol–1提升至-94.3 kcal mol–1，其主要来源为强π堆积相互作用。进一步研究表明，共晶5相较于化合物4具备更优异的热稳定性与爆轰性能，这证实了通过共晶实现的非共价修饰是构建多组分晶体体系的有效手段，同时凸显了共晶形成物对含能材料性能的调控能力。