• Tetrafluorobromate;
  • Cesium;
  • Single crystal X-ray diffraction;
  • Crystal structure;
  • Rietveld refinement


Alkali and alkaline earth metal tetrafluorobromates MIBrF4, MII(BrF4)2 (MI = Na–Cs, MII = Sr, Ba) can be synthesized from the respective fluorides and BrF3. By the reaction of CsF with an excess of BrF3, the compound cesium tetrafluoridobromate(III) bromine trifluoride (1/1), CsBr2F7 (1), was obtained in the form of a colorless powder and as single crystals. Shown by X-ray diffraction on single crystals, its Br2F7 anion is neither planar, nor is its Br–μ-F–Br unit linear, as previously deduced by Raman spectroscopy. In stoichiometric reactions of CsF with BrF3, the compound cesium tetrafluoridobromate(III), CsBrF4 (2), was obtained as a colorless powder. Compound 2 can also be obtained from compound 1 by evacuation. The crystal structure of CsBrF4 (2) was elucidated by Rietveld refinement on its X-ray powder pattern. Its structure is not isotypic to MBrF4 (M = Na, K, Rb, NO) but isotypic to CsAuF4. CsBr2F7 is, however, not isostructural to CsAu2F7.