Crystal structure of the quaternary compounds Li 1.25Cd 1.67In 0.47Cl 6 and Li 0.21Mn 1.71In 0.79Cl 6

Abstract

The quaternary chlorides “Li MInCl 6” ( M=Mg, Mn, Fe, Co, and Cd) reveal high lithium ion conductivity [Solid State Ionics 95 (1997) 173]. Single crystals of the cadmium and the manganese compounds are grown from melts of stoichiometric mixtures of the binary chlorides. The structures of the crystals were determined by X-ray single-crystal techniques. The obtained white Li 1.25Cd 1.67In 0.47Cl 6 crystals crystallize in a highly disordered CdCl 2-type structure (space group R 3 ̄ m , Z=1, a=379.2(1) and c=1767.2(4) pm, R 1=6.23%, 108 unique reflections ( I>2 σ I )). The octahedral metal ion 3 a site of the structure is randomly occupied by Li +, Cd 2+, and In 3+ ions. An additional amount of Cd 2+ ions is localized in the Van der Waals gap on the likewise octahedral interstitial 3 b site. This CdCl 2-type structure obviously corresponds to the structure of the high-temperature polymorphs of the quaternary chlorides under discussion. The pale pink Li 0.21Mn 1.71In 0.79Cl 6 crystals, the structure of which is obviously that of the room-temperature polymorphs of this series, crystallize in a filled AlCl 3-type, ordered CdCl 2 superstructure (space group C2/ m, Z=2, a=642.0(1), b=1110.6(2), and c=629.2(4) pm, β=110.08(3)°, R 1=3.83%, 423 unique reflections ( I>2 σ I )). Of the two metal ions sites the 2 b site is occupied by the Li + and In 3+ ions, the 4 g solely by Mn 2+ ions. In the Van der Waals gap of this structure no electron density is observed. The distortion factors ρ and σ of CdCl 2-type structures [J. Solid State Chem. 95 (1991) 176] are discussed with respect to occupation of interstitial sites in the Van der Waals gap.