Polymorphism and Disorder in Pseudo-One-Dimensional Compounds AMTS4 (A...NH4, K; M...Cu, Ag; T...Mo,W)

The title compounds are synthesized either in aqueous or in methanolic solution from reactions of the tetrathiometallates A2TS4 with salts of the mint metals. Single crystals of KCuMoS4, alpha-KCuWS4 and beta-KCuWS4 could be obtained. Their crystal structures were determined from single crystal diffractometer data. KCuMoS4 (a = 7.929, c = 5.409Ä, space group I-4) and beta-KCuWS4 (a = 7.948, c = 5.452Ä, space group I-4) are basically isotypic with (NH4)CuMoS4, but show some disorder with respect to the potassium postitions and the Cu and Mo positions, respectively. alpha-KCuWS4 (a = 8.494, c = 5.4905Ä, space group P4/nbm) represents a new structure type, which transforms slowly to the more densley packed beta-modification. The transformation is topotactic. Powder diagrams of the silver containing phases (NH4)AgMoS4 (a = 7.960, c = 5.802Ä) and (NH4)AgWS4 (a = 7.971, c = 5.839Ä) indicate isotypy to KcuMoS4.