Synthese, Kristallstruktur und Festkörper‐NMR‐spektroskopische Untersuchung des Oxonitridosilicates BaSi6N8O

Synthesis, Crystal Structure and Solid‐State NMR Spectroscopic Investigation of the Oxonitridosilicate BaSi6N8O The phase‐pure oxonitridosilicate BaSi6N8O has been synthesized starting from BaCO3 and silicon diimide Si(NH)2 in a radiofrequency furnace at temperatures below 1630 °C as a coarsely crystalline colorless material. The structure has been determined by single‐crystal X‐ray diffraction analysis (BaSi6N8O, space group Imm2 (no. 44), a = 810.5(2), b = 967.8(2), c = 483.7(1) pm, V = 379.4(2)·106 pm3, Z = 2, R1 = 0.014, 618 independent reflections, 44 parameters). The oxonitridosilicate comprises a three‐dimensional network structure of corner sharing SiN4 and SiON3 tetrahedra with Ba2+ located in the resulting voids. BaSi6N8O is isostructural with the oxonitridoalumosilicate (sialon) Sr2AlxSi12−xN16−xO2+x (x ≈ 2) that previously has been described in the literature. Furthermore, the anionic network of BaSi6N8O derives from that of the homeotypic reduced nitridosilicate SrSi6N8 by a topotactic insertion of oxygen into the Si–Si single bonds. In the 29Si MAS‐NMR spectrum two sharp isotropic signals have been observed at −54.0 and −56.3 ppm, respectively. With respect to their observed intensity ratio of 1 : 2.1(1) these two signals have to be attributed to the central atoms of SiON3 and SiN4 tetrahedra, respectively, which is in accordance with the X‐ray crystal structure determination (Si at Wyckoff positions 4d (SiON3) and 8e (SiN4)).