The Bihalide Ions ClHCl- and BrHBr-: Crystal Structures of Cesium Chloride-⅓-(Hydronium Bichloride) and Cesium Bromide-⅓-(Hydronium Bibromide)

The compositions and crystal structures of the unusual substances cesium chloride-⅓-(hydronium bichloride), CsCl·⅓-H3OHCl₂, and cesium bromide-⅓-(hydronium bibromide), CsBr·⅓H₃OHBr₂, have been established from three-dimensional X-ray studies of single crystals of these materials. The conventional R factors for the data collected by film methods are 0.093 and 0.085, respectively. Both substances crystallize in space group P6₃/m of the hexagonal system with six formula units per cell. At room temperature the lattice parameters for the chloride complex are a = 10.28 ± 0.02, c = 6.78 ± 0.02 A; those for the bromide complex are a = 10.65 ± 0.02, c = 7.08 ± 0.02 Å. Both compounds have strings of hydronium ions parallel to the c axis. Cesium is coordinated to nine halide ions which are all involved in hydrogen bonds. A string of bichloride ions is parallel to the c axis in CsCl · ⅓H₃OHCl₂ as is a string of bibromide ions in the bromine compound. The bichloride ion has a Cl-H-Cl distance of 3.14 ± 0.02 Å; the corresponding distance in the bibromide ion is 3.35 ± 0.02 Å.