Refinements of the crystal structures and UV-absorption properties of KBrO3, RbBrO3 and CsBrO3

Abstract

Abstract The crystal structures of KBrO3, RbBrO3 and CsBrO3 at 295 K have been refined from single crystal MoKα x-ray data: Rhombohedral R3m, Z = 1:KBrO3, a = 4.4104(2) Å, α = 85.961(8)°, 2393 reflections (337 unique) resulted in R(F) = 0.040; RbBrO3, a = 4.4913(2) Å, α = 87.618(7)°, 2183 reflections (335 unique) resulted in R(F) = 0.047; CsBrO3, a = 4.6525(2) Å, α = 88.749(5)°, 2365 reflections (298 unique) resulted in R(F) = 0.023. The [BrO3]− ions form pyramids with Br–O of (3*) 1.651(2) [K], 1.653(2) [Rb] and 1.654(1) [Cs] Å and O–Br–O of (3*) 104.64(5)° [K], 104.31(6)° [Rb] and 104.50(4)° [Cs]. Including oxygens at (3*) 2.838(2) [K], 2.902(2) [Rb] and 3.055(2) [Cs] Å the Br coordinations can be described as trigonally distorted octahedral, and the overall structures as trigonally distorted perovskites, isostructural with RbClO3, TlClO3, NH4ClO3 and NH4BrO3. INDO calculations of the UV transition energies based on the refined bromate anion geometries were found in full agreement with experimental results, suggesting that the differences in ionic potentials cause constant shifts in the bromate energy levels, preserving their energy differences.