Creating cyclo-N_5^+ cation and assembling N_5^+N_5^- salt via electronegativity co-matching in tailored ionic compounds

The recent discovery of crystalline pentazolates marks a major advance in polynitrogen science and raises prospects of making the long-touted potent propellant N_5^+N_5^- salt. However, despite the synthesis of cyclo-N_5^- anion in pentazolates, counter cation cyclo-N_5^+ remains elusive due to the strong oxidizing power of pentazole ion; moreover, pure N_5^+N_5^- salt is known to be unstable. Here, we devise a new strategy for making rare cyclo-N_5^+ cation and assembling the long-sought N_5^+N_5^- salt in tailored ionic compounds, wherein the negative/positive host ions act as oxidizing/reducing agents to form cyclo-N_5^+/N_5^- species. This strategy is implemented via an advanced computational crystal structure search, which identifies XN_5N_5F (X = Li, Na, K) compounds that stabilize at high pressures and remain viable at ambient pressure-temperature conditions based on ab initio molecular dynamics simulations. This finding opens an avenue for creating and stabilizing N_5^+N_5^- salt assembly in ionic compounds, where cyclo-N_5 species are oxidized/reduced via co-matching with host ions of high/low electronegativity. The present results demonstrate novel polynitrogen chemistry, and these findings offer new insights and prospects in the design and synthesis of diverse chemical species that exhibit unusual charge states, bonding structures, and superior functionality.