Non‐Condensed (Oxo)Nitridosilicates: La 3 [SiN 4 ]F and the Polymorph o‐La 3 [SiN 3 O]O

The isotypic compounds La 3 [SiN 4 ]F and La 3 [SiN 3 O]O were synthesized in a radio‐frequency furnace at 1600 °C. The crystal structures [ Pnma (no. 62), Z = 4; La 3 (SiN 4 )F: a = 9.970(3), b = 7.697(2), c = 6.897(2) Å, V = 529.3(3) Å 3 ; La 3 (SiON 3 )O: a = 9.950(2), b = 7.6160(15), c = 6.9080(14) Å, V = 523.48(18) Å 3 ] were elucidated from single‐crystal X‐ray diffraction data and corroborated by Rietveld refinement, lattice‐energy calculations (Madelung part of lattice energy, MAPLE) and Raman/FTIR spectroscopy. Both compounds are homeotypic with Na 2 Pr[GeO 4 ]OH forming a network of vertex‐sharing FLa 6 /OLa 6 octahedra, whose voids are filled with non‐condensed SiN 4 /SiN 3 O tetrahedra. o‐La 3 [SiON 3 ]O is the orthorhombic polymorph of this compound, which probably represents the high‐temperasture modification, whereas the tetragonal polymorph t‐La 3 [SiON 3 ]O represents the low‐temperature modification. While the space group of the t‐polymorph [ I 4/ mcm (no. 140)] differs from the new La 3 [SiN 4 ]F and o‐La 3 [SiN 3 O]O, the crystal structure contains the same linking pattern.