Ein neuer Typ ternärer Cobaltsulfide A9Co2S7 (A documentclass{article}pagestyle{empty}begin{document}$ buildrel wedge over = $end{document} K,Rb, Cs) mit trigonalplanaren [CoS3]-Baugruppen des zwei- und dreiwertigen Cobalts

A New Type of Ternary Cobalt Sulphide, A₉Co₂S₇ (A $ buildrel wedge over = $ K, Rb or Cs), containing Trigonal-Planar [CoS₃] Units of Two- and Three-Valent Cobalt The passage of a stream of hydrogen over an alkali carbonate/cobalt/sulphur melt resulted in the preparation of the compounds K₉Co₂S₇, Rb₉Co₂S₇ and Cs₉Co₂S₇. The structure of the potassium compound (Space group P2₁3, Z = 4) could be determined from X-ray diffraction experiments on single crystals whilst X-ray investigations of powdered samples of the rubidium and caesium compounds indicate isotypic atomic arrangements with K₉Co₂S₇. The characteristic structural elements of these compounds are trigonal-planar [CoS₃]-units of two- and three-valent cobalt. The results from investigations of the magnetic properties of these ternary cobalt sulphides are in agreement with those expected for mixed-valent Co^II/Co^III structures. The analogously-composed ferrates are closely structurally-related to these sulphides and show corresponding magnetic properties [1].