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 Ln ScS 3 , when appropriate amounts of cesium bromide (CsBr) are present as flux. These Ln ScS 3 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 GdFeO 3 -type structure with Z = 4. Thus, [ScS 6 ] 9− octahedra ( d (Sc S) = 253–259 pm) share common vertices to build up a ∞ 3 {[ScS 6/2 ] 3− } framework with the topology of a cubic perovskite. According to its orthorhombic distortion the former cuboctahedral holes adapt to the early Ln 3+ 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 Ln ScS 3 representatives with Ln = La, Pr, Nd and Sm clearly prefer the centrosymmetric ( Pnma ) and not the non-centrosymmetric space group ( Pna 2 1 ) as previously suggested elsewhere. Single crystals of Pr 3 ScS 6 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 U 3 ScS 6 -type structure. Here, [ScS 6 ] 9− octahedra share trans- oriented edges to create ∞ 1 {[ScS 4/2 S' 2/1 ] 5− } chains along [001], which are held together by Pr 3+ cations (alongside extra S 2− anions) in seven- and eightfold sulfur coordination. Moreover, optical properties, such as the lacking SHG and the Raman spectrum for LaScS 3 , and the different colors (yellow for LaScS 3 versus black for La 2 S 3 and colorless for Sc 2 S 3 ) are discussed, based on non-bonding S 2− ···S 2− distances.