Structural Relationship between the Mg‐Containing Nitridosilicates Ca₂Mg[Li₄Si₂N₆] and Li₂Ca₂[Mg₂Si₂N₆]

Abstract

Abstract Ca 2 Mg[Li 4 Si 2 N 6 ] and Li 2 Ca 2 [Mg 2 Si 2 N 6 ] were synthesized in sealed tantalum ampules with Li as a fluxing agent. Both compounds crystallize in the monoclinic space group C 2/ m (no. 12). The crystal structures were solved and refined on the basis of single‐crystal X‐ray diffraction data [ Z = 2; Ca 2 Mg[Li 4 Si 2 N 6 ]: a = 5.9059(12), b = 9.817(2), c = 5.6109(11) Å, β = 94.90(3)°, R 1 = 0.015, wR 2 = 0.049; Li 2 Ca 2 [Mg 2 Si 2 N 6 ]: a = 5.5472(11), b = 9.844(2), c = 5.9978(12) Å, β = 97.13(3)°, R 1 = 0.024, wR 2 = 0.053]. Ca 2 Mg[Li 4 Si 2 N 6 ] is isomorphic to Ca 3 [Li 4 Si 2 N 6 ] and its crystal structure is homeotypic to that of Li 2 Ca 2 [Mg 2 Si 2 N 6 ]. Both structures are built up of edge‐sharing [Si 2 N 6 ] 10– tetrahedra (bow‐tie units). In the nitridolithosilicate Ca 2 Mg[Li 4 Si 2 N 6 ] the bow‐tie units are connected via pairs of LiN 4 tetrahedra, whereas in the nitridomagnesosilicate Li 2 Ca 2 [Mg 2 Si 2 N 6 ] the nitridosilicate substructure is connected by chains of MgN 4 tetrahedra. Ca 2 Mg[Li 4 Si 2 N 6 ] is only the second example of fourfold planar rectangular coordinated Mg 2+ in a nitridosilicate. Li 2 Ca 2 [Mg 2 Si 2 N 6 ] is the first nitridosilicate with Li + in threefold coordination. The crystal structures were confirmed by lattice‐energy calculations (MAPLE), EDX measurements, and powder X‐ray diffraction.