Synthesis and crystal structure of gold–silver sulfoselenides: morphotropy in the Ag3Au(Se,S)2 series

Gold–silver sulfoselenides of Ag 3 Au(Se,S) 2 series—Ag 3 AuSe 1.5 S 0.5 , Ag 3 AuSeS, and Ag 3 AuSe 0.5 S 1.5 —have been synthesized by fusing the elements in the required stoichiometric amounts in evacuated quartz ampoules. The single crystal X-ray diffraction data indicate the existence of two solid-solution series: petzite-type cubic Ag 3 AuSe 2 —Ag 3 AuSeS (space group I 4 1 32) and trigonal Ag 3 AuSe 0.5 S 1.5 —Ag 3 AuS 2 (space group ). Both crystal structures differ in the distribution of Ag + /Au + cations in the same distorted body-centered cubic sublattice of chalcogen anions. The morphotropic transformation results from the shrinkage of anion packing accompanied by the shortening of Ag–Ag distances. The structure of uytenbogaardtite mineral, earlier incorrectly interpreted as a tetragonal or cubic cell, is similar to that of the trigonal Ag 3 AuS 2 end-member.