Rivalry Under Pressure - The Coexistence of Ambient-pressure Motifs and Close-packing in Silicon Phosphorus Nitride Imide SiP2N4NH

摘要： Non-metal nitrides such as BN, Si3N4 and P3N5 meet numerous demands on high-performance materials and their high-pressure polymorphs exhibit outstanding mechanical properties. Herein, we present the silicon phosphorus nitride imide SiP2N4NH featuring six-fold coordinated Si. Using the multianvil technique, SiP2N4NH was obtained from 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 combination of single-crystal X-ray diffraction and solid-state NMR measurements. Moreover, SiP2N4NH 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 high-pressure chemistry of non-metal nitrides.