LiCa4Si4N8F and LiSr4Si4N8F: Nitridosilicate Fluorides with a BCT‐Zeolite‐Type Network Structure

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: P21/c (no. 14), a = 10.5108(3), b = 9.0217(3), c = 10.3574(3) Å, β = 117.0152(10)°, R1 = 0.0422, wR2 = 0.0724, Z = 4; LiSr4Si4N8F: P4nc (no. 104), a = 9.3118(4), b = 9.3118(4), c = 5.5216(2) Å, R1 = 0.0160, wR2 = 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.