Anionic N18 Macrocycles and a Polynitrogen Double Helix in Novel Yttrium Polynitrides YN6 and Y2 N11 at 100 GPa

Abstract

Two novel yttrium nitrides, YN₆ and Y₂ N₁₁ , were synthesized by direct reaction between yttrium and nitrogen at 100 GPa and 3000 K in a laser-heated diamond anvil cell. High-pressure synchrotron single-crystal X-ray diffraction revealed that the crystal structures of YN₆ and Y₂ N₁₁ feature a unique organization of nitrogen atoms-a previously unknown anionic N₁₈ macrocycle and a polynitrogen double helix, respectively. Density functional theory calculations, confirming the dynamical stability of the YN₆ and Y₂ N₁₁ compounds, show an anion-driven metallicity, explaining the unusual bond orders in the polynitrogen units. As the charge state of the polynitrogen double helix in Y₂ N₁₁ is different from that previously found in Hf₂ N₁₁ and because N₁₈ macrocycles have never been predicted or observed, their discovery significantly extends the chemistry of polynitrides.

Keywords: High-Pressure Chemistry; Inorganic Double Helix; Macrocycles; Polynitrides.