The synthesis and structure of new transition metal lithium calcium nitride compounds

Three new nitrides, Li3Ca2V0.79Nb0.21N4, Li2Ca2.67Nb0.33N3 and Li12Ca9W5N20, were synthesized in sealed niobium tubes using lithium nitride as a flux at temperatures ranging from 800 °C to 1050 °C. In all of these compounds, the transition metals are coordinated tetrahedrally by nitrogen; these tetrahedra are isolated from each other.
• Li3Ca2V0.79Nb0.21N4, space group P21/m (no. 11), cell parameters a=5.7669(8) Å, b=6.9123(9) Å, c=6.0116(12) Å, β=90.727(9)°, Z=2, has a shared vanadium/niobium tetrahedral position which shares vertices with the tetrahedrally-coordinated lithium position.
• Li2Ca2.67Nb0.33N3, space group Req \o(3,¯)m (no. 166), cell parameters a=3.6311(2) Å, c=29.459(3) Å, Z=3, contains a disordered tetrahedral calcium/niobium position, an octahedral calcium position and a triangularly coordinated lithium position.
• Li12Ca9W5N20, space group C2/c (no. 15), cell parameters a=27.7347(19) Å, b=8.6652(6) Å, c=10.7685(7) Å, β=110.314(2)°, Z=4, contains three crystallographically different tungsten positions as well as one disordered lithium position.

Crystal structure of Li3Ca2V0.79Nb0.21N4 depicting the chains of edge-sharing LiN4 (light hatching) and (V/Nb)N4 (dark hatching) tetrahedra viewed approximately along the [100] direction. Calcium atoms are shown as open circles and nitrogen atoms are colored black.Figure optionsDownload as PowerPoint slideHighlights
► Three new lithium calcium nitrides are synthesized.
► Lithium nitride flux used in synthesis.
► Structures contain isolated tetrahedrally coordinated transition metals.
► Li12Ca9W5N20 contains three crystallographically different W positions.