Homologous silver bismuth chalcogenide halides (N, x)PI: Syntheses and crystal structures of the (0,1)P compound AgBi2S2Cl3 and of three members of the (1, x)P solid solution series Ag2xBi4-2xS6-4xBr4x

AgBi2S2Cl3 and three members of the Ag2xBi4-2xS6-4xBr4x solid solution (x = 0.50 (I), x = 0.64 (II), and x = 0.73 (III)) were synthesized from Bi2S3, AgX and BiSX (X = Cl, Br) at 720 K. X-ray diffraction on single crystals revealed that the compounds crystallize in the monoclinic space groups C2/m (No. 12) with a = 1257.3(3), b 400.0(1), c = 804.1(2) pm, beta = 111.0(1)degrees for AgBi2S2Cl3, a 1331.3(5), b = 408.0(2), e = 972.0(3) pm, beta = 90.8(1)degrees for (I), a = 1328.9(4), b = 408.5(1), c = 973.4(4) pm, beta = 90.9(1)degrees for (II), and a = 1332.4(3), b = 409.3(1), c = 974.3(2) pm, beta = 90.4(1)degrees for (III). AgBi2S2Cl3 adopts a variant of the InBi2S4Cl structure type, the isostructural compounds (I), (II) and (III) are related to the orthorhombic FeUS3 type. All four compounds belong to homologous series with general formula [BiSX](2)(.)[AgxBi1-xS2-2xX2x-1](N + 1) (X = Cl, Br), which resemble minerals of the pavonite series. They are characterized by the parameters N and x and are denoted P-(N,P- x) In the crystal structures, two kinds of layered modules, A and B, alternate. Modules of type B are composed of chains of edge-sharing [MBr(4)Z(2)] octahedra (M = Ag/Bi; X = Cl, Br; Z = S/Z) and vary in thickness N. Modules of type A uniformly consist of rows of paired monocapped trigonal prisms around Bi atoms with [MS(4)Z(2)] octahedra around mixed-occupied metal positions (M = Ag/Bi) between them. AgBi2S2Cl3 comprises modules of type A only (N = 0) and is the silver-rich end-member (x = 1) in the series P-(0,P- x). (I) to (III) belong to the P-(1,P- x) series with B modules of thickness N = 1. Calculations of the electronic band structures indicate that the compounds should act as indirect semiconductors with band gaps between 1.5 and 0.6 eV.