Rubidium and Cesium Nitrides: Towards Recoverable Hexazine Rings

Following the ambient conditions synthesis of the aromatic pentazolate [N5]-, its six-membered counterpart, the aromatic hexazine [N6]4- ring, is the next frontier in high-energy density nitrogen chemistry. Targeted for synthesis since 1980, [N6]4- has only recently been produced in the complex K9N56 compound at 46 GPa. However, being partly composed of weakly bonded neutral N2 dimers, K9N56 could not be recovered to ambient conditions. Through the investigation of the Rb-N and Cs-N systems up to 130 GPa, this proposal aims at forming compounds comprised of the same exotic [N6]4- anion—also expected from theoretical calculations—and at recovering them to ambient conditions. The solids’ crystal structure will be determined by single-crystal X-ray diffraction, also employed to assess the novel materials’ recoverability to ambient conditions. This study will complete the investigation of all binary alkali-nitrogen systems, enabling to evidence trends in their high-pressure behavior.