Rivalry under Pressure: The Coexistence of Ambient-Pressure Motifs and Close-Packing in Silicon Phosphorus Nitride Imide SiP2 N4 NH.

Non-metal nitrides such as BN, Si3 N4 , and P3 N5 meet numerous demands on high-performance materials, and their high-pressure polymorphs exhibit outstanding mechanical properties. Herein, we present the silicon phosphorus nitride imide SiP2 N4 NH featuring sixfold coordinated Si. Using the multi-anvil technique, SiP2 N4 NH was obtained by high-pressure high-temperature synthesis at 8 GPa and 1100 °C with in situ formed HCl acting as a mineralizer. Its structure was elucidated by a combination of single-crystal X-ray diffraction and solid-state NMR measurements. Moreover, SiP2 N4 NH was characterized by energy-dispersive X-ray spectroscopy and (temperature-dependent) powder X-ray diffraction. The highly condensed Si/P/N framework features PN4 tetrahedra as well as the rare motif of SiN6 octahedra, and is discussed in the context of ambient-pressure motifs competing with close-packing of nitride anions, representing a missing link in the high-pressure chemistry of non-metal nitrides.