Barium bis[tetrafluoridobromate(III)]

The crystal structure of Ba[BrF4]2 was refined against single-crystal X-ray diffraction data collected at 100 K, confirming the previous model from powder data.


Structure description
The first synthesis of Ba[BrF 4 ] 2 was performed by Sharpe & Emelé us (1948) by treating anhydrous barium chloride or barium fluoride with bromine trifluoride. The product was, however, only characterized by means of a quantitative elemental analysis. The thermal properties of Ba[BrF 4 ] 2 were later studied by Kiselev and co-workers, who investigated the thermal decomposition of Ba[BrF 4 ] 2 to yield barium fluoride (Kiselev et al., 1987). To the best of our knowledge, our report on the crystal structure of Ba[BrF 4 ] 2 determined from X-ray and neutron powder diffraction data at 300 K was the first structural investigation of the title compound (Ivlev et al., 2014). We showed that Ba [BrF 4 ] 2 crystallizes in the space group I4 and adopts the Ba[AuF 4 ] 2 structure type. Here we present our results on the re-refinement of the crystal structure of Ba[BrF 4 ] 2 from single-crystal X-ray diffraction data at 100 K.

Synthesis and crystallization
Tiny crystals of barium tetrafluoridobromate(III) were obtained by direct reaction of bromine trifluoride with barium fluoride in a closed Teflon vessel. In contrast to Rb

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. Because of very small size of the crystals, we had to employ a diffractometer with a Cu source to improve the reflection intensities at the cost of a more complicated absorption correction.

Funding information
We thank the Deutsche Forschungsgemeinschaft for generous funding.

Figure 2
The crystal structure of Ba[BrF 4 ] 2 in a projection along the b axis. Displacement ellipsoids are shown at the 50% probability level.

Figure 1
The closest contacts between one [BrF 4 ] À anion and surrounding Ba 2+ cations. Displacement ellipsoids are shown at the 50% probability level.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.