Sodium chloride induced nitrogen salt with cyclo-N₅ anions at high pressure

Abstract

The energy landscape of sodium chloride-nitrogen mixtures has been comprehensively explored to examine the ability of the formation of unknown compounds under pressures of up to 100 GPa, using swarm-intelligence structure prediction methodology and first-principles calculations. We identified a thermodynamically stable NaN5ClN5 compound containing two cyclo-N5 species under pressures exceeding 53 GPa, representing milder conditions in comparison to those requisite for pure solid nitrogen. In NaN5ClN5, the high electron affinity of the cyclo-N5 motif allows it to oxidize the chlorine atoms, resulting in the formation of two cyclo-N5 anions. Additionally, the weak covalent interactions between Cl and nearby N atoms plays a key role in stabilization of structure. It has been demonstrated that simple NaN5 salt was a suitable precursor for the synthesis of NaN5ClN5 at high pressure. Ab initio molecular dynamics simulations demonstrated the recoverability of NaN5ClN5 as a metastable phase at ambient pressure-temperature conditions. Additionally, NaN5ClN5 exhibits a higher energy density of 3.86 kJ/g and a lower mass density of 1.67 g/cm3 in comparison to metal pentazolate salts, highlighting its potential as a high energy-density material.