Abstract
AbstractThiosilicates of the Rare‐Earth Elements: IV. The quasi‐isostructural Compounds NaSm3S3[SiS4], CuCe3S3[SiS4], Ag0,63Ce3S2,63Cl0,37[SiS4] and Sm3S2Cl[SiS4] – Synthesis, Crystal Structure and Investigations of the Silver‐Cation MotionThe four lanthanoid(III) thiosilicates NaSm3S3[SiS4] (1), CuCe3S3[SiS4] (2), Ag0,63Ce3S2,63Cl0,37[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.
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More From: Zeitschrift für anorganische und allgemeine Chemie
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