The Low‐Valent Bismuth Sulfide Bromide Cu₃Bi₂S₃Br₂

Abstract

Abstract The thermal reactions of Cu with CuBr and Bi 2 S 3 yielded black, shiny needles of the mixed‐valent compound Cu 3 Bi 2 S 3 Br 2 = (Cu I ) 6 (Bi II 2 )(Bi III ) 2 S 6 Br 4 . This first low‐valent copper bismuth chalcogenide halide crystallizes in the orthorhombic space group Pbam with a = 2966.9(7) pm, b = 802.4(2) pm, and c = 389.1(3) pm at 293(2) K. The crystal structure is dominated by ${2}\atop{\infty}$ [Bi 4 S 6 Br 4 ] 6– layers parallel to (100). The copper(I) cations fill trigonal or tetrahedral voids in the packing of anions. The bismuth(III) cations are in monocapped trigonal prismatic coordination. The bismuth(II) cations form Bi 2 4+ dumbbells (Bi–Bi 306.3(3) pm) that are pairwise combined in cyclic fragments [(Bi II 2 ) 2 S 4 Br 4 ] 4– . The structural information on the ordering of the dumbbells is not properly transferred between neighboring layers, resulting in diffuse X‐ray scattering along a *. Raman spectroscopy shows a resonance at 113 cm –1 , which can be attributed to the vibration of the Bi 2 4+ unit.