Synthesis, Crystal Structures and Spectroscopic Properties of RbBaTaS4 and K2BaTa2S11

Abstract

Single crystals of RbBaTaS4 (1) and K2BaTa2S11 (2) were obtained from the reactions of Ta, with in situ formed fluxes of A2S3 (A = K, Rb), BaS, and S at 500 °C. Compound 1 crystallizes in the orthorhombic space group Pnma with a = 9.3286(5), b = 7.0391(4), c = 12.4365(7) Å, V = 816.6(1) Å3, Z = 4. Compound 2 crystallizes in the monoclinic space group P21/c with a = 14.5280(10), b = 12.6347(7), c = 17.5148(12) Å , β = 94.744(8)°, V = 3203.9(4) Å3, Z = 4. The structure of RbBaTaS4 (1) consists of isolated tetrahedral [TaS4]3− anions and Rb+ and Ba2+ cations. The Ba2+ cations are surrounded by nine sulfur atoms forming distorted tricapped trigonal prisms, whereas the Rb+ cations are in an irregular environment of ten sulfur atoms. The structure of K2BaTa2S11 (2) consists of two different dinuclear [Ta2S11] units which are separated by Ba2+ and K+ cations. The Ta atoms are coordinated by S2 2− and S2− ligands according to the mode [Ta2(μ2-S)(μ2-η2,η1- S2)2(η2-S2)2(S)2]4−. Each Ta atom is surrounded by seven sulfur ions forming strongly distorted pentagonal bipyramids. The two [TaS7] polyhedra share a common face in the [Ta2S11] unit. The K+ and Ba2+ cations are statistically distributed over the crystallographic sites. Compound 2 has also been characterized by UV/Vis diffuse reflectance, IR and Raman spectroscopy