Prediction of Methylcyclopentane-Shaped N6 Building Bolcks and Fused N22 Macro-Rings in Potassium Chloride Nitrogen Salts at High Pressure

Polymeric nitrogen has garnered significant research interest due to its unique physicochemical properties and substantial potential as a propellant. Tailored ionic compounds, as emerging inducers, actively enrich the topology of polymeric nitrogen frameworks by enhancing their stability and reactivity through synergistic interactions. Here, we identify the pressure-stabilized methylcyclopentane-shaped N₆ building blocks and fused N₂₂ macro-rings in thermodynamically stable KClN₆ and KClN₁₀ compounds, respectively, employing swarm-intelligence structure prediction methodology and first-principles calculations. Notably, differing from known N₆ benzene rings found in metal hexanitrides, the unique arrangement of the methylcyclopentane-shaped N₆ building block is attributed to the dual actions of ionic and covalent interactions between Cl and nearby N atoms, which help maintain the integrity of the polymeric form. Ab initio molecular dynamics simulations and phonon spectra calculations demonstrated the potential retrieval of KClN₆ as a metastable phase under atmospheric conditions. KClN₆ exhibits desirable characteristics of high energy release, low mass density, high detonation velocity, and high detonation pressure, highlighting its potential as a high energy-density material. These findings provide a new route for the creation of polymeric nitrogen in customized ionic compounds and stimulate experimental search.