Ba18F18In8S21 and Ba9F10In4S10: new kind of mixed anion compounds with the novel low-dimensional structure

Low-dimensional mixed anion compounds Ba18F18In8S21 (1) and Ba9F10In4S10 (2), are synthesized and characterized. These compounds crystallize in the space group P42/ncm(138) with a = b = 22.0703(8) A, c = 12.6143(9) A, and V = 6144.4(6) A3 (Z = 4) for 1 and Pnma(62) with a = 12.5686(8) A, b = 19.2822(12) A, c = 12.5835(9) A, and V = 3049.6(3) A3 (Z = 4) for 2. Compound 1 contains the unusual one-dimensional fluorite type [Ba16F18] ionic region and [BaIn8S21] covalent region, whereas 2 has a two-dimensional fluorite type [Ba2F2] block and the unique tetranuclear [In4S10]8− anion. The first principles electronic structure calculation performed with density functional theory (DFT) indicates that the two compounds are both direct band semiconductors with a gap of 2.28 eV for 1 and 2.23 eV for 2.