Hexazine

While a neutrally charged hexazine species has not yet been synthesized, two negatively charged variants, [N₆]^2- and [N₆]^4-, have been produced in potassium-nitrogen compounds under very high pressures (> 40 GPa) and temperatures (> 2000 K). In particular, [N₆]^4- is aromatic, respecting Hückel's rule, while [N₆]^2- is anti-aromatic.

Stability

The hexazine molecule bears a structural similarity to the very stable benzene molecule. Like benzene, it has been calculated that hexazine is likely an aromatic molecule. Despite this, it has yet to be synthesized. Additionally, it has been predicted computationally that the hexazine molecule is highly unstable, possibly due to the lone pairs on the nitrogen atoms, which may repel each other electrostatically and/or cause electron-donation to sigma antibonding orbitals. A figure-8-shaped isomer is predicted to be metastable.