High-Pressure Synthesis of Nitrogen-Rich Y(N₅)₃·N₂ Pentazolate with Perovskite Topology

The discovery and stabilization of the cyclo-N₅⁻ anion have introduced a class of pentazolate compounds with significant potential as high-energy-density materials (HEDMs). This potential could be further enhanced by increasing the pentazolate-to-metal ratio. Here, we report the high-pressure, high-temperature synthesis and characterization of a novel yttrium pentazolate, Y(N₅)₃·N₂, which exhibits an exceptionally high nitrogen-to-metal ratio of 17:1. Y(N₅)₃·N₂ was synthesized from yttrium and nitrogen by laser heating to 3000 K at 125 GPa in a diamond anvil cell. Its crystal structure, a 3D nitrogen-inclusion metal-pentazolate framework, was solved and refined in situ using synchrotron single-crystal X-ray diffraction. This structure demonstrates a perovskite topology, as pentazolate ring centers form octahedra connected via vertices, neutral nitrogen dimers are located at the centers of the octahedra, and yttrium atoms occupy distorted cuboctahedra within the octahedral 3D framework. Density functional theory (DFT) calculations corroborate the experimental findings and provide further insights into the stability and properties of the synthesized compound. Y(N₅)₃·N₂ is the first example of stabilizing three pentazolate anions per metal cation, surpassing the previously achieved 1:1 ratio. Additionally, we propose a centroid-based structure typification for solvent-free inorganic pentazolates, serving as an important step for further structural classification of pentazolates and other polynitrides.