The intergrowth structure of Ag1.2Bi17.6S23Cl8 and its relation to the tubular structure of Bi6+δ S6+3δ Cl6-3δ and the pavonite homologue Ag3x Bi5-3x S8-6x Cl6x-1

The crystal structures of two members of the solid solution series Bi6+δ S6+3δ Cl6-3δ and of Ag1.2Bi17.6S23Cl8 have been determined by single-crystal X-ray diffraction at room temperature. Single-crystals used for the investigations were obtained from a reaction involving Bi2S3 and AgCl in the molar ratio 3:2 at 740 K. Bi6+δ S6+3δ Cl6-3δ compounds crystallize in the hexagonal space group P63/m (no. 176) with a=11.427(2) A, c=4.071(1) A, for δ=0.64, and a=11.540(2) A, c=4.040(1) A, for δ=0.86 (Z=1). The disordered structure of Bi6+δ S6+3δ Cl6-3δ is closely related to the ordered rhombohedral structure of Bi4S5Cl2. It consists of parallel six-membered ring channels of face- and edge-sharing bicapped trigonal prisms around Bi atoms with additional Bi atoms on the central axes. Ag1.2Bi17.6S23Cl8 adopts the monoclinic space group C2/m (no. 12) with a=53.036(9) A, b=4.030(1) A, c=11.643(4) A, β=94.4(1)o, Z=2. Ag1.2Bi17.6S23Cl8 adopts a new structure type that can be interpreted as a periodic layered intergrowth of modules from Bi6+δ S6+3δ Cl6-3δ and the pavonite homologue Ag3x Bi5-3x S8-6x Cl6x-1 ((2,x)P) along [1 0 0]. The detailed geometrical analysis reveals a remarkable similarity of the interface in the three structures. - Graphical abstract: The intergrowth structure of Ag1.2Bi17.6S23Cl8 highlighting the two alternating types of structural units