High-Pressure Yttrium Nitride, Y5N14, Featuring Three Distinct Types of Nitrogen Dimers

Yttrium nitride, Y5N14, was synthesized by direct reaction between yttrium and nitrogen at ∼50 GPa and ∼2000 K in a laser-heated diamond anvil cell. High-pressure single-crystal X-ray diffraction revealed that the crystal structure of Y5N14 (space group P4/mbm) contains three distinct types of nitrogen dimers. Crystal chemical analysis and ab initio calculations demonstrated that the dimers [N2]x− are crystallographically and chemically nonequivalent and possess distinct noninteger formal charges (x) that make Y5N14 unique among known compounds. Theoretical computations showed that Y5N14 has an anion-driven metallicity, with the filled part of its conduction band formed by nitrogen p-states. The compressibility of Y5N14, determined on decompression down to ∼10 GPa, was found to be uncommonly high for dinitrides containing +3 cations (the bulk modulus K0 = 137(6) GPa).