On the Rubidium Thiotellurate(IV) Rb₂[TeS₃] and its Tritohydrate Rb₂[TeS₃] ⋅ ¹/₃ H₂O

Abstract Rb 2 [TeS 3 ] and Rb 2 [TeS 3 ] ⋅ 1 / 3 H 2 O were obtained from rubidium azide (RbN 3 ), tellurium and sulfur in 2 : 1 : 3 molar ratios from evacuated fused silica ampoules at 500 °C under more or less anhydrous conditions. Both compounds crystallize orthorhombically in the space group P 2 1 2 1 2 1 (Rb 2 [TeS 3 ]: a =873.42(6) pm, b =1316.73(9) pm, c =2064.59(14) pm; Rb 2 [TeS 3 ] ⋅ 1 / 3 H 2 O: a =872.97(6) pm, b =1299.82(9) pm, c =2148.26(15) pm, both at –173 °C for Z = 12) and contain discrete ψ 1 ‐tetrahedral [TeS 3 ] 2− anions ( d (Te−S)=232–236 pm) in layerwise arrangements. The difference results from the water of hydration in Rb 2 [TeS 3 ] ⋅ 1 / 3 H 2 O, which increases the coordination numbers of half of the six crystallographically distinct Rb + cations from six and seven (only sulfur) to seven and almost eight by providing with oxygen from H 2 O an extra ligand ( d (Rb−O)=290–318 pm). Red Rb 2 [TeS 3 ] transforms pseudo ‐topotactically into yellow Rb 2 [TeS 3 ] ⋅ 1 / 3 H 2 O immediately upon contact with moist atmosphere. The compounds were screened with X‐ray diffraction, Raman and diffuse reflectance spectroscopy as well as thermal analysis.