Time-of-flight neutron diffraction study on lithium dinitride iodide, Li7N2I

The structure of Li₇N₂I has been redetermined from neutron diffraction data using the high resolution powder diffractometer (HRPD) at the spallation source ISIS, UK. The title compound crystallizes in the space group F4¯3m (No.216), a=1038.797(1) pm with eight formula units per unit cell. The Li₇N₂I-structure comprises a cationic Li₁₃N₄^staggered+ framework which is built of monocapped octahedra. While all Li atoms at the vertices are shared between two neighbouring units, the capping metal atom is shared by four octahedra. The Li₁₃N₄^staggered+ network is closely related to the B₂X₆ octahedral framework observed in the pyrochlore structure. Large voids in the structure are occupied by iodide and a Li⁺T ion pair. There is evidence that the nonsphericity of the Li⁺I⁻ dipole induces a complicated Lidisorder in the Li-N framework.