Pr 3 S 2 Cl 2 [AsS 3 ]: A Praseodymium(III) Sulfide Chloride Thioarsenate(III) with Double Chains of Condensed [SPr 4 ] 10+ Tetrahedra

Single crystals of Pr 3 S 2 Cl 2 [AsS 3 ] were obtained by reacting praseodymium sesquisulfide and trichloride with arsenic and sulfur (molar ratio: 7:4:6:9) in torch‐sealed evacuated silica ampoules at 850 °C for a week and subsequent slow cooling to room temperature. The transparent, pale yellowish green platelets crystallize monoclinically (Pr 3 S 2 Cl 2 [AsS 3 ]: a = 2190.96(9) pm, b = 685.49(3) pm, c = 701.87(3) pm, β = 98.752(3)°) in the non ‐centrosymmetric space group Cc with Z = 4. The crystal structure of Pr 3 S 2 Cl 2 [AsS 3 ] comprises three crystallographically different Pr 3+ cations. (Pr1) 3+ and (Pr2) 3+ exhibit bicapped trigonal prismatic environments of five sulfur and three chlorine atoms (C.N. = 8) each, whereas only seven sulfur atoms arranged as capped trigonal prism (C.N. = 7) are present in the case of (Pr3) 3+ . Two of the five crystallographically different sulfur atoms (S1 and S2) are coordinated by four Pr 3+ cations, each in the shape of slightly distorted [SPr 4 ] 10+ tetrahedra ( d (S–Pr) = 278–294 pm). Hence, the crystal structure of Pr 3 S 2 Cl 2 [AsS 3 ] contains double chains with the composition 1 ∞ {[S 2 Pr 3 ] 5+ }, consisting of two parallel edge‐fused chains of anti ‐SiS 2 ‐analogous single strands 1 ∞ {[SPr 2 ] 4+ }, formed by trans ‐edge sharing [SPr 4 ] 10+ tetrahedra. The arrangement of the 1 ∞ {[S 2 Pr 3 ] 5+ } double chains running along [001] can be described as a hexagonal rod‐packing. Chloride anions (Cl1 and Cl2) as well as the isolated, ψ 1 ‐tetrahedral thioarsenate(III) groups [AsS 3 ] 3– ( d (As–S) = 228–229 pm) consisting of three sulfur atoms (S3, S4, and S5) and an As 3+ cation carrying a stereochemically active non ‐bonding electron pair take care of the three‐dimensional interconnection and the charge balance of the 1 ∞ {[S 2 Pr 3 ] 5+ } double chains. All lone pairs at the As 3+ cations of the [AsS 3 ] 3– pyramids point in the same direction parallel to the c axis of the acentric crystal structure of Pr 3 S 2 Cl 2 [AsS 3 ].