CsTb3STe4 and CsTb5S2Te6: two pseudo-ternary cesium terbium chalcogenides with ordered S2- and Te2-anions

By the oxidation of terbium metal with sulfur and tellurium in the presence of cesium bromide as flux at 850 degrees C for 10 days, the first quaternary cesium terbium chalcogenides with ordered S2- and Te2- anions could be obtained as main products. The new compounds CsTb3S2Te4 and CsTb5S2Te6 occur as black needles. While CsTb3S2Te4 crystallizes in the orthorhombic space group Pnma with a = 1924.08(16), b = 433.61(3) and c=1493.47(13) pm for Z=4, CsTb5S2Te6 adopts the monoclinic space group C2/m with a = 21/16.17(18), b = 431.42(3), c = 1049.68(9) pm and beta=102.064(3)degrees for Z= 2. Both crystal structures are characterized by parallel cationic and anionic strands ((1)(infinity){[STb3](7+)) and (1)(infinity) {[CsTe4](7-)} for CsTb3STe4 as well as (1)(infinity){[S2Tb5](11+)} and (1)(infinity){[CsTe6](11-)} for CsTb5S2Te6), all running along [010]. The cationic chains result from vertex-connected [STb4](10+) tetrahedra (d(S2--Tb3+) = 271 277 pm), whereas face-sharing bicapped trigonal or square prisms [CsTe6+2](15-) or [CsTe8+2](19)(-), respectively, form their anionic counterparts.