On the Centrosymmetric Lanthanoid Scandium Sulfides LnScS3 (ln = La, Pr, Nd and Sm) and the Crystal Structure of Pr3ScS6

Reactions of selected lanthanoids (Ln = La, Pr, Nd and Sm), scandium and sulfur in 1:1:3 M ratios at 750 °C for seven days in glassy silica ampoules yielded single crystals of LnScS3, when appropriate amounts of cesium bromide (CsBr) are present as flux. These LnScS3 representatives crystallize in the orthorhombic space group Pnma with the lattice parameters a = 719.51(5), b = 959.82(6), c = 654.27(4) pm for Ln = La, a = 713.92(5), b = 953.47(6), c = 648.13(4) pm for Ln = Pr, a = 711.67(5), b = 951.30(6), c = 645.81(4) pm for Ln = Nd and a = 706.84(5), b = 948.93(6), c = 642.78(4) pm for Ln = Sm, adopting the centrosymmetric GdFeO3-type structure with Z = 4. Thus, [ScS6]9− octahedra (d(ScS) = 253–259 pm) share common vertices to build up a ∞3{[ScS6/2]3−} framework with the topology of a cubic perovskite. According to its orthorhombic distortion the former cuboctahedral holes adapt to the early Ln3+ cations to provide them an eightfold sulfur coordination (d(Ln–S) = 276–334 pm). The high quality structure refinements from single-crystal X-ray diffraction data leave no doubt that all LnScS3 representatives with Ln = La, Pr, Nd and Sm clearly prefer the centrosymmetric (Pnma) and not the non-centrosymmetric space group (Pna21) as previously suggested elsewhere. Single crystals of Pr3ScS6 occurred as by-product, crystallizing with a = 1386.41(9), b = 1656.08(11), c = 393.46(3) pm orthorhombically in the space group Pnnm with the U3ScS6-type structure. Here, [ScS6]9− octahedra share trans-oriented edges to create ∞1{[ScS4/2S'2/1]5−} chains along [001], which are held together by Pr3+ cations (alongside extra S2− anions) in seven- and eightfold sulfur coordination. Moreover, optical properties, such as the lacking SHG and the Raman spectrum for LaScS3, and the different colors (yellow for LaScS3 versus black for La2S3 and colorless for Sc2S3) are discussed, based on non-bonding S2−···S2− distances.