Direct Observation of Cyclo-Pentazolate Anion Decomposition in a Tailored Molecular Trap

The cyclo-pentazolate anion (cyclo-N₅ ^-) has garnered significant attention as an all-nitrogen, five-membered-ring ion with a high energy state and unique aromaticity. Typically, the free cyclo-N₅ ^- anion is a highly unstable species, and its stabilization relies on strong interactions, such as a hydrogen bonding network or metal coordination. However, these interactions often compromise the independence of the anion, thus diminishing its aromaticity. Herein, we present a molecular trap designed to encapsulate and isolate cyclo-N₅ ^- through collective weak interactions. This approach utilizes a pre-positioned ion to subsequently displace the cyclo-N₅ ^- anion into the cage cavity, addressing the challenge posed by the absence of strong-interaction-driven binding. This setup preserves the aromaticity of the anion to a significant extent, as predicted by computational studies. More importantly, the decomposition of free cyclo-N₅ ^- within the microenvironment was directly recorded for the first time using single-crystal X-ray diffraction analysis.