  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.
