A NEW-TYPE OF TERNARY COBALT SULFIDE, A(9 )CO(2)S(7) (A=K, RB OR CS),CONTAINING TRIGONAL-PLANAR [COS3] UNITS OF 2-VALENT AND 3-VALENT COBALT

The passage of a stream of hydrogen over an alkali carbonate/cobalt/su lphur melt resulted in the preparation of the compounds K9Co2S7, Rb9CO 2S7 and CS9Co2S7. The structure of the potassium compound (Space group P2(1)3, 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 arrangeme nts with K9Co2S7. The characteristic structural elements of these comp ounds 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 mixe d-valent Co-II/Co-III structures. The analogously-composed ferrates ar e closely structurally-related to these sulphides and show correspondi ng magnetic properties [1].