Syntheses, crystal structures and spectroscopic properties of KEu[AsS 4], K 3Dy[AsS 4] 2 and Rb 4Nd 0.67[AsS 4] 2

Abstract

Three rare earth compounds, KEu[AsS 4] ( 1), K 3Dy[AsS 4] 2 ( 2), and Rb 4Nd 0.67[AsS 4] 2 ( 3) have been synthesized employing the molten flux method. The reactions of A 2S 3 (A = K, Rb), Ln (Ln = Eu, Dy, Nd), As 2S 3, S were accomplished at 600 °C for 96 h in evacuated fused silica ampoules. Crystal data for these compounds are: 1, monoclinic, space group P2 1/ m (no. 11), a = 6.7276(7) Å, b = 6.7190(5) Å, c = 8.6947(9) Å, β = 107.287(12)°, Z = 2; 2, monoclinic, space group C2/ c (no. 15), a = 10.3381(7) Å, b = 18.7439(12) Å, c = 8.8185(6) Å, β = 117.060(7)°, Z = 4; 3, orthorhombic, space group Ibam (no. 72), a = 18.7333(15) Å, b = 9.1461(5) Å, c = 10.2060(6) Å, Z = 4. 1 is a two-dimensional structure with 2 ∞[Eu(AsS 4)] − layers separated by potassium cations. Within each layer, distorted bicapped trigonal [EuS 8] prisms are linked through distorted [AsS 4] 3− tetrahedra. Each Eu 2+ cation is coordinated by two [AsS 4] 3− units by edge-sharing and bonded to further two [AsS 4] 3− units by corner-sharing. Compound 2 contains a one-dimensional structure with 1 ∞[Dy(AsS 4) 2] 3− chains separated by potassium cations. Within each chain, distorted bicapped trigonal prisms of [DyS 8] are linked by slightly distorted [AsS 4] 3− tetrahedra. Each Dy 3+ ion is surrounded by four [AsS 4] 3− moieties in an edge-sharing fashion. For compound 3 also a one-dimensional structure with 1 ∞[Nd 0. 67(AsS 4) 2] 4− chains is observed. But the Nd position is only partially occupied and overall every third Nd atom is missing along the chain. This cuts the infinite chains into short dimers containing two bridging [As 4] 3− units and four terminal [AsS 4] 3− groups. 1 is characterized with UV/vis diffuse reflectance spectroscopy, IR, and Raman spectra.