Aromatic Hexazine [N6]4- Anion Revealed in the Complex Structure of the High-Pressure Potassium Nitride K9N56

Recent high-pressure synthesis of pentazolates and subsequent stabilization of the aromatic [N5]- anion at atmospheric pressure had an immense impact on nitrogen chemistry. Here, we present the first synthesis of an aromatic hexazine [N6]4- anion realized in high-pressure potassium nitride K9N56 at 46 and 61 GPa. The extremely complex structure of K9N56 was solved based on synchrotron single-crystal X-ray diffraction and corroborated by density functional theory calculations. This result resolves a long-standing question of the aromatic hexazine stability and the possibility of its synthesis.