Neue Sulfido-Antimonate der schweren Alkalimetalle: Synthese, Kristallstruktur und chemische Bindung von (K/Rb/Cs)3SbS3 und Cs3SbS4H2O

The new sulfido antimonates(III) (Rb/Cs)3SbS3 were prepared from the alkali metal sulfides Rb2S/Cs2S2 and elemental antimony and sulfur or Sb2S3 at reaction temperatures of about 700 ◦C. The known isotypic potassium compound was similarily synthesized from the elements. The structures of the light-yellow crystals were refined using single-crystal X-ray data. Both compounds are isotypic to the respective Na salt forming the Na3AsS3 structure type (cubic, space group P213, K/Rb/Cs: a = 947.21(7)/982.28(5)/1025.92(5) pm, Z = 4, R1 = 0.0159/0.0560/0.0582). The ψtetrahedral SbS3− 3 anions with Sb−S bond lengths of 242 pm are arranged in a cubic face centered packing, in which the three crystallographically different A+ cations occupy the tetrahedral and octahedral voids, overall exhibiting a distorted octahedral sulfur coordination. The chemical bonding and the characteristics of the stereochemically active lone electron pair have been investigated by means of FP-LAPW band structure calculations. Needle-shaped crystals of the monohydrate of the antimony(V) salt Cs3SbS4 ·H2O were obtained from a suspension of Sb2O3, CsOH and elemental sulfur. Cs3SbS4 ·H2O crystallizes in a new structure type (monoclinic, space group P21/c, a = 987.17(10), b = 994.83(7), c = 1600.46(14) pm, β = 126.895(8)◦, Z = 4, R1 = 0.0234). As expected, the Sb−S distances (233.1 – 234.7 pm) in the nearly ideally tetrahedral anion SbS3− 4 are considerably shorter than in the antimonates(III) but match the bond lengths in the anhydrous sulfido antimonate(V) Cs3SbS4. Due to their similar fcc-like anion packing and the stereochemically active lone electron pair of Sb in the antimonates(III), the whole series of compounds A 3SbS3/4 shows a uniform structure relation, which is elucidated using crystallographic group-subgroup relations.