A team of scientists from the University of Manchester and University of Oxford has successfully synthesized stable nitrogen chain radical anions under ambient conditions, a significant advancement in the field of chemistry. Their findings, detailed in a study published on February 28, 2026, in the journal Nature Chemistry, reveal new possibilities for the study and application of these highly reactive molecules.
Nitrogen Chain Reactivity and Its Challenges
Long-chain nitrogen ions and radicals, consisting of more than three nitrogen atoms, are known for their high reactivity. These molecules are typically only stable under extreme conditions, such as ultrahigh pressure, which makes them challenging to isolate and study in typical laboratory settings. Their propensity to release nitrogen gas (N2) during decomposition adds to their appeal as potential high-energy-density materials, suitable for applications in propellants, explosives, and gas generators.
The authors of the study note, “Studying nitrogen chain ions under ambient conditions presents a formidable challenge, and a better understanding of their electronic structures should reveal a wealth of hitherto untapped chemical space.” Previous attempts to isolate these nitrogen chains in laboratory settings have met with limited success, often altering their properties or failing to achieve full characterization.
Breakthrough in Stability Under Ambient Conditions
In this notable research endeavor, the team isolated five crystalline molecules featuring unsupported tetra-nitrogen radical anion ({N4}•−) chains. This was accomplished by reducing para-substituted phenyl azides with potassium graphite, a process that enabled the stabilization of the nitrogen chains under ambient conditions. One specific derivative, identified as [(4-BrC6H4)2N4]•−, demonstrated remarkable longevity, remaining stable for six weeks when stored under anaerobic conditions.
The study found that the radical character of the molecule was primarily delocalized across the N4 chain, particularly at the terminal nitrogen atoms. While several derivatives were successfully isolated and examined, some exhibited instability and even exploded upon isolation. The research team elaborated, “Although changes in spin density across the {N4} chain and stability with aromatic substitution are observed, the computational and experimental electronic structure studies into the series are consistent with the {N4} chains having partial multiple bond character with substantial radical character on the terminal nitrogen atoms bonded to the aromatic units.”
Further investigations into stability and reactivity were conducted with various reagents and conditions. Results indicated the potential for the N4 chain to cleave into N1 and N3 fragments, acting as a source of nitrene radical anions. This discovery suggests that the synthesized molecules could serve as storable nitrogen group transfer reagents, paving the way for safer and more efficient uses of nitrogen in industrial applications.
The study authors concluded, “Efforts are now focused on exploring the additional reactivity patterns of {N4}•−-containing molecules, to enhance our understanding of their chemical properties and to fully unlock their potential as gram-scale storable nitrene synthons.”
This breakthrough in nitrogen chemistry not only advances scientific knowledge but also opens new avenues for practical applications, potentially transforming how reactive nitrogen species are utilized in chemical synthesis.