Gerüstverbindungen mit beweglichen LaIII‐Kationen: Synthesen,Kristallstrukturen und Strukturdynamik der Lanthan(III)‐Eisen(II)‐Sulfid‐Halogenide La53Fe12S90X3 (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 La₅₃Fe₁₂S₉₀X₃ (X = Cl, Br, I) Black crystals of La₅₃Fe₁₂S₉₀X₃ (X = Cl, Br, I) were synthesized from La₂S₃ and FeS in a reactive LaX₃ flux at 1320 K. The structures were determined by single‐crystal X‐ray diffraction. The compounds are isostructural, crystallizing in the rhombohedral space group with Z = 1 (La₅₃Fe₁₂S₉₀Cl₃: a = 14.0154(7), c = 21.888(1) Å, V = 3723.5(3) ų; La₅₃Fe₁₂S₉₀Br₃: a = 14.0048(9), c = 22.040(2) Å, V = 3743.6(4) ų; La₅₃Fe₁₂S₉₀I₃: a = 13.9805(8), c = 22.108(2) Å, V = 3742.2(4) ų). The structure adopted is a stuffed variant of the La₅₂Fe₁₂S₉₀ structure type. [Fe^II₂S₉] dimers of face‐sharing octahedra are linked by face‐ and vertex‐sharing bi‐ or tri‐capped [La^IIIS_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 La₅₂Fe₁₂S₉₀, are filled by halide ions in La₅₃Fe₁₂S₉₀X₃. 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.