Aromaticity is an electronic property of cyclic molecular structures that confers enhanced stability, enabling these molecular species to persist in otherwise impossible environments. In particular, nitrogen-only molecules are known to be notoriously unstable, and therefore prime targets for achieving aromaticity in order to make them significantly more appealing for potential technological applications.
Hexaazabenzene, an N6 ring analogous to the most well-known aromatic species, benzene, has been shortlisted as a promising candidate. A variety of configurations and geometries have been proposed based on calculations, including that of the hexazine anion [N6]4–, but up until now, its experimental synthesis was not achieved.
A CSEC-based team applied extreme pressure and temperature conditions to synthesize a remarkably complex K9N56 compound which is comprised of the [N6]4– hexazine ring. The K9N56 compounds was formed under pressure of 46 GPa and temperatures above 2000 K, and characterized with single-crystal X-ray diffraction at the ESRF and DESY synchrotrons. The [N6]4– ring is found to be aromatic, respecting all of Hückel’s rule along with more advanced criteria as demonstrated by density functional theory calculations.
This study, which is published in Nature Chemistry, brings to a close a more-than 40 years old quest for an aromatic hexazine unit. The demonstration of its existence will give materials scientists and chemists a clear target for its synthesis at normal pressure conditions. On account of its aromaticity, and thereby of its expected increased stability, the [N6]4– ring is a prime candidate for technological applications.