Über Münzmetall‐Quecksilber‐Chalkogenidhalogenide. II Hydrothermalsynthese,Kristallstruktur und Phasenumwandlung von CuHgSCl und CuHgSBr

On Coinage Metal Mercury Chalcogenide Halides II: Hydrothermal Synthesis, Crystal Structure, and Solid State Phase Transition of CuHgSCl and CuHgSBr The hydrothermal reaction of CuCl and CuBr with HgS in concentrated aqueous HX (X = Cl, Br) as solvent at 670 K in sealed glass ampoules yields yellow‐orange crystals of CuHgSCl and CuHgSBr. Both compounds crystallize isotypically (orthorhombic, Pbam, a = 984.01(8), b = 1775.1(2), c = 409.59(3) pm for CuHgSCl and a = 1003.7(4), b = 1833.6(5), c = 412.4(2) pm for CuHgSBr, Z = 8). The structures consist of plane folded HgS chains connected by pairs of distorted CuS₂X₂ tetrahedra sharing the X—X‐edge (X = Cl, Br) in which the copper atoms occupy off‐centered positions. The large displacement factors of the Cu atoms represent thermal vibrations as shown by additional X‐ray investigations at different temperatures. The single‐crystal structure determination shows that the earlier structure model, based on powder diffraction data, is incorrect. The structure type of CuHgSCl und CuHgSBr shows distinct similarities to the structure type of the already known compounds CuHgSeBr, AgHgSBr and AgHgSI (MHgYX). At 323 K CuHgSBr undergoes a second order phase transition into a higher symmetric structure of the MHgYX type (orthorhombic, Pmam, a = 1009.2(3), b = 918.40(4), c = 413.81(2) pm) with halved b‐axis.