SYNTHESIS AND CRYSTAL-STRUCTURE DETERMINATION OF (NH4)AG2ASS4, A FURTHER CHALCOPYRITE-TYPE COMPOUND

Crystals of (NH4)Ag2AsS4 were synthesized from an approximately equimolar mixture of Ag, As2S3, and S in ammonia solution under hydrothermal conditions. The crystals are tetragonal: a = 6.780(1) Å, c = 8.277(1) Å, space group I4̄2m, Z = 2. The structure was determined from a Patterson map (277 single crystal X-ray data) and refined to final residual parameters of R = 0.031 and Rw = 0.028. In a first coordination sphere the atoms Ag and As as well as the NH4 group are equidistant 4-coordinated to S atoms. The crystal structure represents a distorted chalcopyrite-type framework. The Ag-S bonds in the AgS4 polyhedron of (NH4)Ag2AsS4 exhibit a pronounced covalent character, deduced from the comparison of about twenty AgS4 polyhedra mentioned in the literature. © 1993 Academic Press, Inc.