Sulfosalts with Alkaline Earth Metals. Centrosymmetric vs Acentric Interplay in Ba₃Sb_4.66S₁₀ and Ba_2.62Pb_1.38Sb₄S₁₀ Based on the Ba/Pb/Sb Ratio. Phases Related to Arsenosulfide Minerals of the Rathite Group and the Novel Polysulfide Sr₆Sb₆S₁₇

Abstract

The new compounds, Sr6Sb6S17, Ba2.62Pb1.38Sb4S10, and Ba3Sb4.66S10 were prepared by the molten polychalcogenide salt method. Sr6Sb6S17 crystallizes in the orthorhombic space group P212121 with a = 8.2871(9) Å, b = 15.352(2) Å, c = 22.873(3) Å, and Z = 4. This compound presents a new structure type composed of [Sb3S7]5- units and trisulfide groups, (S3)2-, held together by Sr2+ ions. The [Sb3S7]5- fragment is formed from three corner-sharing SbS3 trigonal pyramids. The trisulfide groups are separated from the [Sb3S7]5- unit and embedded between the Sr2+ ions. Ba3Sb4.66S10 and Ba2.62Pb1.38Sb4S10 are not isostructural but are closely related to the known mineral sulfosalts of the rathite group. Ba3Sb4.67S10 is monoclinic P21/c with a = 8.955(2) Å, b = 8.225(2) Å, c = 26.756(5) Å, β = 100.29(3)°, and Z = 4. Ba2.62Pb1.38Sb4S10 is monoclinic P21 with a = 8.8402(2) Å, b = 8.2038(2) Å, c = 26.7623(6) Å, β = 99.488(1)°, and Z = 4. The Sb atoms are stabilized in SbS3 trigonal pyramids that share corners to build ribbonlike slabs, which are stitched by Ba/Pb atoms to form layers perpendicular to the c-axis. These materials are semiconductors and show optical band gaps of 2.10, 2.14, and 1.64 eV for Sr6Sb6S17, Ba3Sb4.66S10, and Ba2.62Pb1.38Sb4S10, respectively. Raman spectroscopic characterization is reported. Sr6Sb6S17, Ba3Sb4.66S10, and Ba2.62Pb1.38Sb4S10 melt congruently at 729, 770, and 749 °C, respectively