Ternäre Nitride des Lithiums mit den Elementen Cr, Mo und W / Ternary Lithium Nitrides with Elements Cr, Mo and W

The ternary compounds were prepared by reaction of the transition metals with Li₃N melt under nitrogen. The crystal structures of Li₆MeN₄ (P4₂/nmc, Z = 2; Me = Mo: a = 667.3(1) pm, c = 492.5(3) pm; Me = W: a = 667.9(1) pm, c = 492.7(1) pm) and Li₁₅Cr₂N₉ (P4/ncc, Z = 4; a = 1023.3(5) pm, c = 938.9(7) pm) can be described as fluorite-type superstructures with the lithium and transition metal atoms in tetrahedral holes of the nearly fcc nitrogen arrangement and with an ordered distribution of defects within the cation substructure. In addition, the ternary system Li–Cr–N contains the compound Li₆CrN₄ with a crystal structure which is not quite clear at present, but which shows close relations to the structures of Li₆MeN₄ (Me = Mo, W). The previously reported compounds Li₉MeN₅ (Me = Cr, Mo, W) have not been observed during this study. The respective Cr compound in fact is a nitride-oxide (nitride-imide) of composition Li₁₄Cr₂N₈(O,NH) with a crystal structure (P3̄, Z = 1, a = 579.9(1) pm, c = 826.3(6) pm) also showing a fluorite-type superstructure.