Synthesis of FeN 4 at 180 GPa and its crystal structure from a submicron-sized grain.

Iron tetra-nitride, FeN ₄ , was synthesized from the elements in a laser-heated diamond anvil cell at 180 (5) GPa and 2700 (200) K. Its crystal structure was determined based on single-crystal X-ray diffraction data collected from a submicron-sized grain at the synchrotron beamline ID11 of ESRF. The compound crystallizes in the triclinic space group P . In the asymmetric unit, the Fe atom occupies an inversion centre (Wyckoff position 1 d ), while two N atoms occupy general positions (2 i ). The structure is made up from edge-sharing [FeN ₆ ] octa-hedra forming chains along [100] and being inter-connected through N-N bridges. N atoms form catena -poly[tetraz-1-ene-1,4-di-yl] anions [-N=N-N-N-] _∞ ^2- running along [001]. In comparison with the previously reported structure of FeN ₄ at 135 GPa [Bykov et al. (2018). Nat. Commun. 9 , 2756], the crystal structure of FeN ₄ at 180 GPa is similar but the structural model is significantly improved in terms of the precision of the bond lengths and angles.