Synthesis and crystal structure of silicon pernitride SiN 2 at 140 GPa.

Silicon pernitride, SiN 2 , was synthesized from the elements at 140 GPa in a laser-heated diamond anvil cell. Its crystal structure was solved and refined by means of synchrotron-based single-crystal X-ray diffraction data. The title compound crystallizes in the pyrite structure type (space group Pa , No. 205). The Si atom occupies a site with multiplicity 4 (Wyckoff letter b , site symmetry ..), while the N atom is located on a site with multiplicity 8 (Wyckoff letter c , site symmetry .3.). The crystal structure of SiN 2 is comprised of slightly distorted [SiN 6 ] octa-hedra inter-connected with each other by sharing vertices. Crystal chemical analysis of bond lengths suggests that Si has a formal oxidation state of +IV, while nitro-gen forms pernitride anions (N-N) 4- .