1-(2-Bromoethyl)-1,4-diazoniabicyclo[2.2.2]octane bromide tetrafluoroborate

In the crystal of the title compound, C8H17BrN2 2+·Br−·BF4 −, a weak intermolecular N—H⋯Br hydrogen bond is observed between the cation and the bromide anion. A two-part disorder model was applied to the BF4 − anion with a refined major–minor occupancy ratio of 0.837 (14):0.163 (14).


Comment
The variable-temperature dielectric response, especially in relatively high frequency range, is very useful for searching phase transitions, in which there is a dielectric anomaly at the transition temperature. Unluckily, the title compound has no dielectric disuniform from 93 K to 453 K( m.p. > 473 K ) and report here.
In this report we have established unambiguously the structure at 293 K of the title compound in the solid state by X-ray diffraction analysis. As shown in Fig. 1. Single crystal X-ray analysis reveals that there are weak hydrogen bonds between 1-(2-bromoethyl)-1,4-diazabicyclo[2.2.2]octane-1,4-diium cation and bromide anion. Experimental 1,4-Diazabicyclo [2.2.2]octane (5.6 g, 0.05 mol) was dissolved in 20 ml of chloroform. To this solution 0.048 mol of 1,2dibromoethane was added at once and the mixture was refluxed for 8 hours. On standing for 16 hours at room temperature, colorless crystals were obtained in large quantity. The crude product was collected and dissolved in 20 ml methanol, and 10ml HBF 4 (1 mol/L) in methanol was added slowly with stirring, while white precipitate formed at once.The suspension was filtered, and dissolved in H 2 O, After a few weeks, colorless crystals were obtained by slow evaporation.

Refinement
Positional parameters of all the H atoms except for H2 were calculated geometrically and the H atoms were set to ride on the C atoms to which they are bonded, with Uiso(H) = 1.2Ueq(C). The H2 on the N2 was freely refined. The BF4-anion was refined using a two-part disorder model with a major:minor occupancy ratio of 84:16%. Distance similarity and mild displacement parameter restraints were applied to the minor component.

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 supplementary materials sup-3 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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.