Preparation and crystal structure of Na 4Cu 2S 3, a thiocuprate with discrete anions

Abstract

Transparent pale yellow crystals of Na 4Cu 2S 3 were obtained from the melt of a corresponding mixture of the binary sulphides. Na 4Cu 2S 3 is tetragonal, space group I4 1 /a with a = 9.468(1) A ̊ , c=36.64(2) A ̊ and Z=16 . The crystal structure was determined from four-circle diffractometer data and refined to a conventional R of 0.021 for 1682 observed reflections with F 0 2> 3 σ( F 0 2) and 83 variables. An outstanding feature of Na 4Cu 2S 3 is the formation of discrete V-shaped thiocuprate anions [SCuSCuS] 4− with copper in an almost linear coordination by sulphur. The bond lengths ( d CuS =2.15 A ̊ ) and angles are in good agreement with those of the infinite anionic chains of KCuS. The crystal structure is based on a cubic close-packed arrangement of sulphur atoms with sodium in the centres of the tetrahedral voids, while copper atoms are shifted from the centres towards one of the edges in order to attain a linear co-ordination.