hexazine

Hexazine (also known as hexaazabenzene) is a hypothetical allotrope of nitrogen composed of 6 nitrogen atoms arranged in a ring-like structure analogous to that of benzene. As a neutrally charged species, hexazine would be the final member of the azabenzene (azine) series, in which all of the methine groups of the benzene molecule have been replaced with nitrogen atoms. The two last members of this series, hexazine and pentazine, have not been observed, although all other members of the azine series have (such as pyridine, pyrimidine, pyridazine, pyrazine, triazines, and tetrazines).

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. The synthesis of the structural isomer, the linear hexanitrogen, C2h-N6, was published in 2025.