1-Bromomethyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide

The title compound, C7H14BrN2 +·Br−, was prepared by nucleophilic substitution of DABCO (systematic name: 1,4-diazabicyclo[2.2.2]octane) with dibromomethane in acetone. The structure features Br⋯H close contacts (2.79 and 2.90 Å) as well as a weak bromine–bromide interaction [3.6625 (6) Å].

We have isolated crystals of the title compound of sufficient quality for crystallographic analysis. Typically, the reaction between dibromomethane and DABCO proceeds quickly in acetone, resulting in the immediate precipitation of the monoalkylated bromide salt that is insoluble in acetone. However, at sufficiently low concentrations of reactants, slow crystallization of the product occurs.

Experimental
Dibromomethane (10 mmol) was added to a solution of DABCO (10 mmol) in acetone (100 ml). Colorless plates of poor quality evolve almost immediately, which after 1 h are filtered. The filtrate is sealed in a flask and left to sit for 1 week, after which prisms suitable for X-ray analysis form on the side of the flask.

Refinement
A structural model consisting of one symmetrically independent molecule was developed. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms were placed in ideal positions and refined as riding atoms. The ideally calculated H atoms on C1, C2, and C5 are related by the symmetry operation (1 -x, y, z). For these H atoms the special position constraints were suppressed to allow for the correct calculation of the idealized H atom positions.
For all H atoms the U iso values were assigned as 1.2 times the carrier U eq . On the basis of 468 unmerged Friedel opposites, the likelihood of inversion twinning is negligible (Flack, 1983;Flack& Bernardinelli, 2000).

Special details
Experimental. One distinct cell was identified using APEX2 (Bruker, 2004). Seven frame series were integrated and filtered for statistical outliers using SAINT (Bruker, 2005) then corrected for absorption by integration using SHELXTL/XPREP V2005/2 (Bruker, 2005) before using SAINT/SADABS (Bruker, 2005) to sort, merge, and scale the combined data. No decay correction was applied. Refinement. Structure was phased by direct methods (Sheldrick, 2008). Systematic conditions suggested the ambiguous space group.