Conferring all-nitrogen aromatics extra stability by acidic trapping

For decades, the all-nitrogen substance tetranitrogen, a promising candidate for eco-friendly use as an ultra-high energy density material, has been of intense interest. Still, its experimental stabilization has never been achieved under ambient conditions. Here, the all-nitrogen aromatic N₄²¯ was found to obtain extra stability in sufficiently high concentration of hydronium ions or ammonium ions, leading to a productive yielding of the ultra-high energy density material for space exploration, high-value defense, and civil applications. The reactivity of N₄²¯ in various acidity was found to be a competition between the aromaticity of N₄²¯ and its proton affinity. At sufficiently high acidity, N₄²¯ begins to resist acid − base neutralization by forming a N₄²¯···4H₃O⁺ complex. The intermolecular hydrogen bonding assists in reducing the mutual repulsion of nitrogen lone pair electrons and enhance the aromaticity of N₄²¯. By thus, the firmness of N₄²¯ was reinforced by 200%, strongly implying a promising application of the current strategy to facilitate the synthesis of N₄²¯. The current strategy of acidic trapping is expected to apply to other all-nitrogen aromatic compounds.