Homologous silver bismuth chalcogenide halides P-(N,P- x). II. The P-(2,P- x) and P-(3,P- x) structure families of modular compounds with tunable composition and structure

摘要

The crystal structures of two members of the solid solution series Ag3xBi5-3xS8-6xCl6x-1 (x = 0.52 (I), x = 0.67 (II)) and three compounds of the Ag(4x)Bi(6-4x)Q(10-8x)Br(8x-2) series (Q = S:x = 0.70 (III), x = 0.84 (IV); Q = Se: x = 0.72 (V)) were determined by single-crystal X-ray diffraction. The compounds crystallize in the monoclinic space group C2/m (No. 12) with a = 1326.7(3), b = 403.9(1), c = 1176.7(2) pm, beta = 107.833(3)degrees for (I); a = 1325.4(3), b = 403.3(1), c = 1170.6(2) pm, beta = 108.14(3)degrees for (II); a = 1338.9(4), b = 409.3(1), c = 1440.7(4) pm, beta = 114.40(1)degrees for (IV); and a = 1370.9(2), b = 417.6(4), c = 1480.4(2) pm, beta = 114.92(2)degrees for (V). (I) and (II) adopt the PbBi4S7 structure type, (III) to (V) crystallize in the CuBi5S8 type. All five compounds belong to the homologous series with general formula [BiQX](2)[Ag(x)Bi(1-x)Q(2-2x)X(2x-) (1)](N+1) (Q = S, Se; X = Cl, Br; 1/2 <= x <= 1)), which resemble minerals of the pavonite series. They are characterized by the parameters N and x and are denoted (N,x)P. In the crystal structures, two kinds of layered modules alternated along [001]. Modules of type A uniformly consist of paired rods of face-sharing monocapped trigonal prisms around Bi atoms with octahedra around mixed occupied metal positions (M = Ag/Bi) between them. Modules of type B are composed of chains of edge-sharing [MZ(6)] octahedra (M = Ag/Bi; Z = Q/X). These NaCl-type fragments are of thickness N = 2 in Ag3xBi5-3xS8-6xCl6x-1 and N = 1 in Ag(4x)Bi(6-4x)Q(10-8x)Br(8x-2). All structures exhibit Ag/Bi disorder in octahedrally coordinated metal positions and Q/X mixed occupation of some anion positions.