High-Pressure Synthesis of Antimony Nitride Sb₃N₅ and Polynitride Sb₂N₈ Featuring Single-Bonded N₈ ^10- Chains

High-pressure high-temperature synthesis in laser-heated diamond anvil cells provides a direct pathway to stabilize polymeric and oligomeric nitrogen units, often inaccessible under ambient conditions due to the stability of the N₂ molecule. Here we report the high-pressure reactivity of antimony with molecular nitrogen, leading to the discovery of two distinct binary nitrides. At megabar pressures, we synthesized and structurally characterized mP20-Sb₂(N₈), the first pnictogen oligonitride containing unprecedented twisted single-bonded (N₈)^10- chains. The compound was identified by single-crystal x-ray microdiffraction and Raman spectroscopy, supported by density functional theory calculations. At lower pressures of ∼ 50 GPa, we observed the formation of oC32-Sb₃N₅, complementing recent reports of this phase by the studies of its compressional behavior and stability field. These results significantly expand the interpnictogen chemistry and demonstrate the ability of antimony to stabilize unusual extended nitrogen fragments at high pressures.