PREPARATION AND CRYSTAL-STRUCTURE OF LITHIUM NITRIDE DIBROMIDE, LI5NBR2

Single phase Li5NBr2 was prepared by the reaction of Li3N and dry, OH-free LiBr under inert gas at 430 degrees C. In the quasi-binary system Li3-2xN1-xBrx Li5NBr2 is the second most nitride rich compound after Li10N3Br. Following unit cell indexing using laboratory X-ray powder data the previously unknown structure of Li5NBr2 was solved from neutron powder diffraction data recorded at the flat-cone and powder diffractometer E2 at the rebuilt reactor BER II in Berlin. The title compound crystallizes in the orthorhombic space group Immm (No. 71), a = 603.79(4), b = 1181.3(1), c = 390.14(3) pm with two formula units per unit cell. The Li-N-sublattice comprises linear chains of vertex sharing Li6N-octahedra which are aligned along the short c-axis and are separated by chains of bromine atoms. The N-Br arrangement may be regarded as an ordered AX? variant of a cubic close packing involving two kinds of atoms. Lithium atoms occupy the tetrahedral holes formed by one nitrogen and three bromine atoms, as well as the N-N edges of the N2Br2 tetrahedra.