Stabilization of Polynitrogen Anions in Tantalum–Nitrogen Compounds at High Pressure

Abstract The synthesis of polynitrogen compounds is of great importance due to their potential as high‐energy‐density materials (HEDM), but because of the intrinsic instability of these compounds, their synthesis and stabilization is a fundamental challenge. Polymeric nitrogen units which may be stabilized in compounds with metals at high pressure are now restricted to non‐branched chains with an average N−N bond order of 1.25, limiting their HEDM performances. Herein, we demonstrate the synthesis of a novel polynitrogen compound TaN 5 via a direct reaction between tantalum and nitrogen in a diamond anvil cell at circa 100 GPa. TaN 5 is the first example of a material containing branched all‐single‐bonded nitrogen chains [N 5 5− ] ∞ . Apart from that we discover two novel Ta–N compounds: TaN 4 with finite N 4 4− chains and the incommensurately modulated compound TaN 2−x , which is recoverable at ambient conditions.