Nitrido-silicate. II [1]. Hochtemperatur-Synthesen und Kristallstrukturen von Sr2Si5N8 und Ba2Si5N8

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Abstract

Sr2Si5N8 und Ba2Si5N8 werden phasenrein durch Umsetzung von Siliciumdiimid mit den jeweiligen Metallen Strontium bzw. Barium unter Stickstoffatmosphäre in einem speziellen Hochfrequenzofen bei 1 550 bis 1 650°C synthetisiert. Sr2Si5N8 (Pmn21, a = 571,0(2), b = 682,2(2), c = 934,1(2) pm, Z = 2, R = 0,037, wR = 0,021) und Ba2Si5N8 (Pmn21, a = 578,3(2), b = 695,9(2), c = 939,1(2) pm, Z = 2, R = 0,022, wR = 0,018) kristallisieren isotyp und sind aus M2+-Ionen (M = Sr bzw. Ba) sowie einer kovalenten dreidimensionalen Raumnetzstruktur eckenverknüpfter SiN4-Tetraeder aufgebaut. Je 4 N sind an zwei bzw. drei Si gebunden. Die an je zwei Si gebundenen N leisten den dominierenden koordinativen Beitrag für die M2+-Ionen.

Abstract

Nitrido-Silicates. II. High Temperature Syntheses and Crystal Structures of Sr2Si5N8 and Ba2Si5N8

Pure Sr2Si5N8 and Ba2Si5N8 were obtained by reaction of silicon diimide with metallic strontium and barium, respectively. The reactions have been carried out under nitrogen atmosphere in a specially developed high-frequency furnace at temperatures between 1 550 and 1 650°C. Sr2Si5N8 (Pmn21, a = 571.0(2), b = 682.2(2), c = 934.1(2) pm, Z = 2, R = 0.037, wR = 0.021) and Ba2Si5N8 (Pmn21, a = 578.3(2), b = 695.9(2), c = 939.1(2) pm, Z = 2, R = 0.022, wR = 0.018) are isotypic and contain M2+ ions as well as a three-dimensional covalent network structure of corner-sharing SiN4 tetrahedra. Two sorts of N occur with molar ratio 1 : 1 which are bonded to two and three Si, respectively. Predominantly, the N which are bonded to two Si belong to the coordination spheres of the M2+ ions.

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