Gerüstverbindungen mit beweglichen La III ‐Kationen: Synthesen, Kristallstrukturen und Strukturdynamik der Lanthan(III)‐Eisen(II)‐Sulfid‐Halogenide La 53 Fe 12 S 90 X 3 ( X = Cl, Br, I)

Framework Compounds with Mobile La III Cations: Syntheses, Crystal Structures and Structural Dynamics of the Lanthanum(III) Iron(II) Sulfide Halides La 53 Fe 12 S 90 X 3 ( X = Cl, Br, I) Black crystals of La 53 Fe 12 S 90 X 3 ( X = Cl, Br, I) were synthesized from La 2 S 3 and FeS in a reactive La X 3 flux at 1320 K. The structures were determined by single‐crystal X‐ray diffraction. The compounds are isostructural, crystallizing in the rhombohedral space group $R{\bar 3}m$ with Z = 1 (La 53 Fe 12 S 90 Cl 3 : a = 14.0154(7), c = 21.888(1) Å, V = 3723.5(3) Å 3 ; La 53 Fe 12 S 90 Br 3 : a = 14.0048(9), c = 22.040(2) Å, V = 3743.6(4) Å 3 ; La 53 Fe 12 S 90 I 3 : a = 13.9805(8), c = 22.108(2) Å, V = 3742.2(4) Å 3 ). The structure adopted is a stuffed variant of the La 52 Fe 12 S 90 structure type. [Fe II 2 S 9 ] dimers of face‐sharing octahedra are linked by face‐ and vertex‐sharing bi‐ or tri‐capped [La III S 6+n ] trigonal prisms, forming a three‐dimensional framework containing cuboctahedral cavities of two sizes. The larger cavities, which remain empty in the structure of La 52 Fe 12 S 90 , are filled by halide ions in La 53 Fe 12 S 90 X 3 . The smaller cavities accommodate numerous sites for disordered lanthanum cations, modelling a network of diffusion pathways through the structure. An analogous picture is obtained from the calculation of the periodic nodal surface (PNS): The PNS separates a labyrinth containing the framework atoms from a labyrinth containing the mobile lanthanum cations. Molecular dynamic simulations confirm a strong coupling between the motions of the mobile lanthanum ions and the neighbouring sulfide ions.