LiCa 4 Si 4 N 8 F and LiSr 4 Si 4 N 8 F were synthesized from Si 3 N 4 , LiNH 2 , CaH 2 /SrH 2 , 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 [LiCa 4 Si 4 N 8 F: P2 1 /c (no. 14), a = 10.5108 (3), b = 9.0217(3), c = 10.3574(3) Å, = 117.0152(10)°, R 1 = 0.0422, wR 2 = 0.0724, Z = 4; LiSr 4 Si 4 N 8 F: P4nc (no. 104), a = 9.3118(4), b = 9.3118(4), c = 5.5216(2) Å, R 1 = 0.0160, wR 2 = 0.0388, Z = 2]. The silicate substructure of both compounds is built up of vertex-sharing SiN 4 tetrahedra, thereby forming a structure analogous to the BCT zeolite with Ca 2+ /Sr 2+ , Li + , and Fions filling the voids. The crystal structure of LiSr 4 Si 4 N 8 F is homeo- [a] Chemistry of LMU Munich) for performing the EDX measurements. Financial support by the Fonds der Chemischen Industrie (FCI) is gratefully acknowledged.