Syntheses and Crystal Structures of PbSbO2Br, PbSbO2I, and PbBiO2Br

Transparent single crystals of PbSbO2Br (green), PbSbO2I, and PbBiO2Br (yellow) were obtained by solid state reactions of stoichionictric amounts of PbO, Pn(2)O(3) (Pn = Sb, Bi) and PnX(3) (X = Br, 1). The crystal structures were determined from single-crystal X-ray data. The title compounds crystallize tetragonally in the space group I4/mmm (No. 139): Lattice constants and refinement values are: PbSbO2Br: a = 3.9463(3), c = 12.849(1) angstrom, V = 200.10(3) angstrom(3), and Z = 2, R-1 = 0.0236, and wR(2) = 0.0513. PbSbO2I: a = 4.0074(3), c = 13.627(2) angstrom, V = 218.84(3) angstrom(3), and Z = 2, R-1 = 0.0244, and wR(2) = 0.0538. PbBiO2Br: a = 3.9818(2), c = 12.766(2) angstrom, V = 202.39(4) angstrom(3), and Z= 2, R-1 = 0.0276, and wR(2) = 0.0715. The compounds are isotypic and crystallize in the anti-ThCr2Si2 structure type with lead and Pn statistically disordered on one common position. In case of Pn = Sb a slight separation of the positions of the cations becomes obvious. Optical bandgaps were detennined by UV/Vis spectroscopy. They are 2.67 eV (PbSbO2Br), 2.48 eV (PbSbO2I), and 2.47 eV (PbBiO2Br).