Synthesis and Comprehensive Studies of Be-IV-N2 (IV = Si, Ge): Solving the Mystery of Wurtzite-Type Pmc21 Structures.

The research for wurtzite-type ternary nitride semiconductors containing earth abundant elements with a stoichiometry of 1:1:2 was focused on metals like Mg or Zn, so far. The vast majority of these Grimm-Sommerfeld analogous compounds crystallize in the ß-NaFeO2 structure, although a second arrangement in space group Pmc21 is predicted to be a viable alternative. Despite extensive theoretical and experimental studies, this structure has so far remained undiscovered. Herein, we report on BeGeN2 in a Pmc21 structure, synthesized from Be3N2 and Ge3N4 using a high-pressure high-temperature approach at 6 GPa and 800 °C. The compound was characterized by powder X-ray diffraction (PXRD), solid state nuclear magnetic resonance (NMR), Raman and energy dispersive X-ray (EDX) spectroscopy, temperature-dependent PXRD, second harmonic generation (SHG) and UV/VIS measurements and in addition also compared to its lighter homologue BeSiN2 in all mentioned analytic techniques. The synthesis and investigation of both the first beryllium germanium nitride and the first ternary wurtzite-type nitride crystallizing in space group Pmc21 open the door to a new field of research on wurtzite-type related structures.

Building Nitridic Networks with Phosphorus and Germanium-from GeIIP2N4 to GeIVPN3.

Nitridophosphates and nitridogermanates attract high interest in current research due to their structural versatility. Herein, the elastic properties of GeP2N4 were investigated by single-crystal X-ray diffraction (XRD) upon compression to 44.4(1) GPa in a diamond anvil cell. Its isothermal bulk modulus was determined to be 82(6) GPa. At 44.4(1) GPa, laser heating resulted in the formation of multiple crystalline phases, one of which was identified as unprecedented germanium nitridophosphate GePN3. Its structure was elucidated from single-crystal XRD data (C2/c (no. 15), a = 8.666(5), b = 8.076(4), c = 4.691(2) Å, ß = 101.00(7)°) and is built up from layers of GeN6 octahedra and PN4 tetrahedra. The GeN6 octahedra form double zigzag chains, while the PN4 tetrahedra are found in single zigzag chains. GePN3 can be recovered to ambient conditions with a unit cell volume increase of about 12%. It combines PV and GeIV in a condensed nitridic network for the first time.

Highly Condensed and Super-Incompressible Be2PN3.

Although beryllium and its compounds show outstanding properties, owing to its toxic potential and extreme reaction conditions the chemistry of Be under high-pressure conditions has only been investigated sparsely. Herein, we report on the highly condensed wurtzite-type Be2PN3, which was synthesized from Be3N2 and P3N5 in a high-pressure high-temperature approach at 9 GPa and 1500 °C. It is the missing member in the row of formula type M2PN3 (M = Mg, Zn). The structure was elucidated by powder X-ray diffraction (PXRD), revealing that Be2PN3 is a double nitride, rather than a nitridophosphate. The structural model was further corroborated by 9Be and 31P solid-state nuclear magnetic resonance (NMR) spectroscopy. We present 9Be NMR data for tetrahedral nitride coordination for the first time. Infrared and energy-dispersive X-ray spectroscopy (FTIR and EDX), as well as temperature dependent PXRD complement the analytical characterization. Density functional theory (DFT) calculations reveal super-incompressible behavior and the remarkable hardness of this low-density material. The formation of Be2PN3 through a high-pressure high-temperature approach expands the synthetic access to Be-containing compounds and may open access to various multinary beryllium nitrides.

Synthesis and crystal structure of silicon pernitride SiN2 at 140†GPa.

Silicon pernitride, SiN2, 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 SiN2 is comprised of slightly distorted [SiN6] 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-.