Thiosilicate der Selten‐Erd‐Elemente: IV. Die quasi‐isostrukturellen Verbindungen NaSm3S3[SiS4], CuCe3S3[SiS4], Ag0,63Ce3S2,63Cl0,37[SiS4] und Sm3S2Cl[SiS4] – Synthese, Kristallstruktur und Untersuchungen zur Silberionendynamik

Abstract

Thiosilicates of the Rare‐Earth Elements: IV. The quasi‐isostructural Compounds NaSm₃S₃[SiS₄], CuCe₃S₃[SiS₄], Ag_0,63Ce₃S_2,63Cl_0,37[SiS₄] and Sm₃S₂Cl[SiS₄] – Synthesis, Crystal Structure and Investigations of the Silver‐Cation Motion The four lanthanoid(III) thiosilicates NaSm₃S₃[SiS₄] (1), CuCe₃S₃[SiS₄] (2), Ag_0,63Ce₃S_2,63Cl_0,37[SiS₄] (3) and Sm₃S₂Cl[SiS₄] (4) crystallize all hexagonally in the non‐centrosymmetric space group P6₃ (no. 173) showing basically the same structure. Besides an eightfold square‐antiprismatic sulfide coordination sphere about the M³⁺ cations these compounds display discrete tetrahedral thiosilicate units [SiS₄]⁴⁻ which are trigonally distorted. All tops of the remaining pyramids point into the same direction along the c axis and therefore the structure needs to be non‐centrosymmetric. However, the main feature of these crystals are channels along [001], built up by non‐silicon bonded sulfide anions and providing trigonal planar (CN = 3) and trigonal antiprismatic (CN = 6) voids. In the sodium derivative (1) the Na⁺ cations reside almost in the center of the latter ones exhibiting a trigonally distorted octahedral surrounding (CN = 6) while the Cu⁺ cations of the respective thiosilicate (2) are situated in the middle of an (S²⁻)₃ triangle (CN = 3), just 7 pm above its plane. The same is true for the silver compound (3) with the exception of the Ag⁺ cations sitting about 53 pm above the sulfide triangle and showing a marked under‐occupation along with a very large U₃₃ displacement parameter. These facts lead to the assumption that (3) could be a promising material for ionic Ag⁺ conduction. In order to maintain electroneutrality the silver derivative has to contain a certain amount of Cl⁻ anions (CeCl₃ was used as fluxing agent) substituting S²⁻ which was doubtlessly confirmed by WDX analyses. In the absence of any monovalent cation (A⁺) the analogous structure is realized in (4) displaying an empty channel along [001] and a complete substitution of one sulfide by one chloride anion per formula unit, also confirmed by electron‐beam microanalysis.