Alkaline earth metal oxyhalides revisited - Syntheses and crystal structures of Sr4OBr6, Ba4OBr6 and Ba2OI2

Abstract

Single crystals of the compounds Ca4OCl6, Sr 4OBr6, Ba4OBr6, and Ba 2OI2 were obtained by solid-state reactions. The crystals of Ba2OI2 are transparent and colorless and isopointal to K2ZnO2 adopting the orthorhombic space group Ibam (no. 72, Z = 4) with the cell parameters a = 747.20(9), b = 1392.02(18), and c = 678.12(9) pm. Sr4OBr6 and Ba4OBr6 are isotypic to Ba4OCl6 (or isopointal to K 6ZnO4) and crystallize in the hexagonal space group P63mc (no. 186, Z = 2) exhibiting the cell parameters a = 982.20(4) and c = 750.41(7) pm for Sr4OBr6 and a = 1030.10(2) and c = 785.92(4) pm for Ba4OBr6. In the ternary systems Ca-O-X (X = Cl, Br or I) the only compound found other than the starting materials was the already known Ca4OCl6 which is also isotypic to Ba4OCl6 crystallizing in the hexagonal space group P6 3mc (no. 186, Z = 2) with the cell parameters a = 903.30(6) and c = 683.27(8) pm. © 2008 Verlag der Zeitschrift für Naturforschung, Tübingen.