Pr4S3[AsS3]2: Praseodym(III)‐Sulfid‐Thioarsenat(III) mit Ketten und Schichten aus kondensierten [SPr4]‐Tetraedern

Abstract

AbstractSingle crystals of Pr4S3[AsS3]2 can be obtained through the reaction between the elements praseodymium, arsenic and sulfur using CsCl as fluxing agent in torch‐sealed evacuated silica ampoules. The starting materials were heated for ten days at 700 °C and then cooled down slowly to room temperature. The transparent, pale greenish yellow platelets crystallize orthorhombically (a = 2910.6(2), b = 699.74(5), c = 704.51(5) pm) in space group Pbcn (no. 60) with Z = 4. The new compound Pr4As2S9 (≡ Pr4S3[AsS3]2) contains two crystallographically independent Pr3+ cations. (Pr1)3+ shows a bicapped trigonal prismatic environment of eight sulfur atoms (CN = 8), whereas (Pr2)3+ is surrounded by only seven sulfur atoms in the shape of a monocapped trigonal prism (CN = 7). The isolated pyramidal thioarsenate(III) anions [AsS3]3– are formed as ψ1‐tetrahedra by the three sulfur atoms (d(As3+–S2–) = 223–228 pm, ∢(S–As–S) = 94–104°) and a non‐binding electron pair (lone pair) at each As3+ cation. Two of the five crystallographically different sulfur atoms (S1 and S2) are not connected to As3+ at all, but coordinated by four Pr3+ cations each to build up slightly distorted [SPr4]10+ tetrahedra (d(S2––Pr3+) = 281–289 pm, ∢(Pr–S–Pr) = 98–146°). Thus the crystal structure of Pr4S3[AsS3]2 exhibits endless {}^1_∞{[(S1)Pr4/2]4+} chains and {}^2_∞{[(S2)Pr4/4]+} layers, which consist of trans‐edge condensed [(S1)Pr4]10+ tetrahedra for the chains and [(S2)Pr4]10+ tetrahedra sharing four common edges for layers. The lone pairs at the As3+ cations close around the{}^1_∞{[(S1)Pr4/2]4+} chains running along [001]. The {}^2_∞{[(S2)Pr4/4]+} layers spread out parallel to the (100) plane and complete the crystal structure of Pr4S3[AsS3]2 according to {}^1_∞{[(S1)(Pr1)4/2]4+}{}^2_∞{([(S2)(Pr2)4/4]+)2} {}^0_∞{([As(S3)(S4)(S5)]3–)2}.