Homologous Silver Bismuth Chalcogenide Halides (N, x) P. III. The (4, x) P, (5, x) P, and (7, x) P Structure Families of Modular Compounds with Tunable Composition and Structure

The crystal structures of six members of the homologous series with general formula [Bi QX ] 2 [Ag x Bi 1−x Q 2−2x X 2x−1 ] N+1 ( Q = S, Se; X = Cl, Br; 1/2 ≤ x ≤ 1) and N = 4, 5, or 7 were determined by single‐crystal X‐ray diffraction. The series are characterized by the parameters N and x and are denoted (N, x) P. Ag 3 Bi 4 S 6 Cl 3 ( x = 0.60) (I) , Ag 3.5 Bi 3.5 S 5 Br 4 ( x = 0.70) (II) and Ag 3.65 Bi 3.35 Se 4.70 Br 4.30 ( x = 0.73) (III) belong to (4, x )P series Ag 5x Bi 7−5x Q 12−10x X 10x−3 and adopt the AgBi 6 S 9 structure type. The (5, x) P compound Ag 3.66 Bi 4.34 S 6.68 Br 3.32 (IV) , which corresponds to x = 0.61 in Ag 6x Bi 8−6x S 14−12x Br 12x−4 , crystallizes isostructurally to AgBi 3 S 5 . The compounds Ag 4.56 Bi 5.44 Se 8.88 Br 3.12 ( x = 0.57) (V) and Ag 5.14 Bi 4.86 S 7.76 Br 4.24 ( x = 0.64) (VI) , which are members of (7, x) P series Ag 8x Bi 10−8x Q 18−16x Br 16x−6 , adopt the Ag 3 Bi 7 S 12 structure type. In the monoclinic crystal structures (space group C 2/ m ) two kinds of layered modules alternate 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 [ MZ 6 ] octahedra, which are arranged in NaCl‐type fragments of thickness N . All structures exhibit Ag/Bi disorder in octahedrally coordinated metal positions as well as Q / X mixed occupation of some anion positions. Corresponding to their black color, all compounds are narrow‐gap semiconductors ( E g = 0.35 eV for (II) ). General characteristics of the entire class of (N, x) P compounds are gathered in a catalogue.