New nitrogen allotrope created at last

Carbon is famous for its allotropes, including humble graphite, flashy diamond, and satisfyingly symmetrical buckminsterfullerene. But allotropes of nitrogen, carbon’s neighbor in the periodic table, are rare and usually fleeting. Now chemists at Justus Liebig University Giessen have created and isolated the neutral nitrogen allotrope hexanitrogen, or N6—a string of six nitrogen atoms held together by four double bonds and one single bond in the molecule’s center. Making hexanitrogen contributes to fundamental scientific knowledge and could offer opportunities for energy storage in the future, say N6’s creators Peter R. Schreiner, Artur Mardyukov, and Weiyu Qian (Nature 2025, DOI: 10.1038/s41586-025-09032-9).Until now, neutral nitrogen allotropes were limited to the common nitrogen found in air (N2), polymeric nitrogen, and molecules that were so short-lived they could be identified only spectroscopically, including the azide radical N3 and a form of N4 that has never been structurally characterized. Chemists have spent decades trying to make neutral nitrogen allotropes, but they’ve typically gone after highly symmetric structures, such as an all-nitrogen version of benzene.The problem with such a molecule, Schreiner says, is that it would be made from alternating single and double bonds between the nitrogen atoms, which would readily convert into triple-bonded N2. “Just stretch it a little, and boom, it goes kaput in no time,” he says.Schreiner, Mardyukov, and Qian realized that to make a neutral nitrogen allotrope stable enough to isolate, they had to create a structure that wouldn’t easily break into N2 units. While hexanitrogen looks like it could dissociate into N3