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Horky, Katrin; Schnick, Wolfgang (2017): LiCa₄Si₄N₈F and LiSr₄Si₄N₈F: Nitridosilicate Fluorides with a BCT-Zeolite-Type Network Structure. In: European Journal of inorganic Chemistry, Nr. 7: S. 1107-1112
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Abstract

LiCa4Si4N8F and LiSr4Si4N8F were synthesized from Si3N4, LiNH2, CaH2/SrH2, and LiF through a metathesis reaction in a radiofrequency furnace. The crystal structures of both compounds were solved and refined on the basis of single-crystal X-ray diffraction data [LiCa4Si4N8F: P2(1)/c (no. 14), a = 10.5108(3), b = 9.0217(3), c = 10.3574(3) angstrom, beta = 117.0152(10)degrees, R-1 = 0.0422, wR(2) = 0.0724, Z = 4;LiSr4Si4N8F: P4nc (no. 104), a = 9.3118(4), b = 9.3118(4), c = 5.5216(2)angstrom, R-1 = 0.0160, wR(2) = 0.0388, Z = 2]. The silicate substructure of both compounds is built up of vertex-sharing SiN4 tetrahedra, thereby forming a structure analogous to the BCT zeolite with Ca2+/Sr2+, Li+, and F- ions filling the voids. The crystal structure of LiSr4Si4N8F is homeotypic with that of Li2Sr4Si4N8O as it exhibits the same zeolite-type [SiN2](2-) framework, but incorporates LiF instead of Li2O. In contrast to the respective Sr compound, LiCa4Si4N8F shows a distortion of the BCT-zeolite-type network as well as an additional site for F. Both F sites in LiCa4Si4N8F exhibit different coordination spheres to LiSr4Si4N8F. The title compounds are the first reported lithium alkaline-earth nitridosilicates containing fluorine. The crystal structures were confirmed by lattice-energy calculations (MAPLE), energy-dispersive X-ray spectroscopy (EDX) measurements, and powder X-ray diffraction. IR spectra confirmed the absence of N-H bonds.