(OLi₂Ca₄)₃[MN₄]₄ (M=Mo, W): Nitridometalate oxides with close structural relationships to the Th₃P₄ type structure

Molybdenum and tungsten powder react readily with alkali and alkaline earth metal nitrides to form nitridometalates. Transparent yellow single crystals of the title compounds are formed in the presence of traces of oxides under flowing nitrogen at 850 degrees C/900 degrees C. The crystal structures were determined by single crystal X-ray analyses (space group I (4) over bar 3d, Z = 4, (OLi2Ca4)(3)[MoN4](4): a = 13.061(3) Angstrom, (OLi2Ca4)(3)[WN4](4): a = 13.060(2) Angstrom). Predominant structural features are isolated tetrahedral complex anions [MoN4](6-) and [WN4](6-), which can be described in accordance with the extended Zintl-Klemm concept. The isolated oxygen atoms are surrounded by four Ca and two Li cations in a tetragonal bipyramidal arrangement with Ca forming the tetragonal basis. The centers of tetrahedra and tetragonal bipyramids form a pattern which resembles the motif of the Th3P4 type structure