Hydrogen-Bond-Driven Co-crystallization of Cyclopentazolate Salts: Anhydrous Energetic Ionic Co-crystals with Tunable Lattice Cohesion and Energetic Performance

Abstract Stabilizing the all-nitrogen cyclopentazolate anion (cyclo-N5−) in condensed phases without energetic dilution remains challenging. Here, first-principles evolutionary crystal-structure prediction yields three anhydrous energetic ionic co-crystals (EICCs): [NH3OH]+[N5]−·H3NO (HAPZO), [NH4]+[N5]−·H3NO (AHPZO), and [N2H5]+[N5]−·N2H4 (HYPZO). For each stoichiometry, searches at 0, 30, and 50 GPa converged to the same structural motif after relaxation to 0 GPa, and phonon calculations confirmed its dynamical stability. In 20 ps fixed-volume canonical-ensemble (NVT) ab initio molecular dynamics (AIMD) simulations, HAPZO, AHPZO, and HYPZO retained structural integrity up to comparative thresholds of 600, 900, and 300 K, respectively. At 1200 K, fragment-resolved internal mean-square displacement (Internal-MSD) and local radial distribution function (RDF) analyses indicate more robust cyclo-N5− rings in HAPZO and AHPZO than in HYPZO, consistent with HYPZO’s weaker N−N integrated crystal orbital Hamilton population (ICOHP) and occupied antibonding character. Cation/co-former selection tunes energetic performance: HAPZO gives the highest detonation velocity and pressure (D = 7.79 km s−1, P = 24.77 GPa), AHPZO combines a density of 1.66 g cm−3 with the strongest calculated lattice cohesion, and HYPZO provides the largest gravimetric and volumetric heats of combustion (11.70 kJ g−1 and 16.95 kJ cm−3). This anhydrous ionic co-crystal strategy enables tuning of ring robustness, lattice cohesion, and energetic performance.