1,1,4,4-Tetramethylpiperazinediium dibromide

A small quantity of the title compound, C8H20N2 2+·2Br−, was formed as a by-product in a reaction between a diamine and an alkyl bromide. The asymmetric unit contains half of a centrosymmetric dication and a bromide anion. In the crystal, weak intermolecular C—H⋯Br hydrogen bonds consolidate the crystal packing.

A small quantity of the title compound, C 8 H 20 N 2 2+ Á2Br À , was formed as a by-product in a reaction between a diamine and an alkyl bromide. The asymmetric unit contains half of a centrosymmetric dication and a bromide anion. In the crystal, weak intermolecular C-HÁ Á ÁBr hydrogen bonds consolidate the crystal packing.

Comment
Low quantity of the title compound ( Fig. 1) was formed as a byproduct in a synthesis between a tetramethylethylenediamine (TMEDA) and ethoxyethylbromide. Most probably residues of dibromoethane existed as an impurity on either of the starting materials as it is known that piperazinium can be formed by reacting TMEDA and 1,2-dibromoethane. The compound has been recrystallized from acetonitrile/methanol solvent and its crystal structure is reported here.
The asymmetric unit consists of one anion and half a cation. The C-H···Br distances vary from 2.826 (30) to 2.924 (20) Å. In the crystal, cations are packed columnary along a axis forming at the same time layers along b axis. The bromide anions are analogously packed between the cation layers. The structure is stabilized by weak intermolecular C-H···Br interactions.
Cation conformation of this compound is similar to those previously reported tetraiodidocadmate and pentabromothallate salts.

Experimental
The compound was a byproduct from a reaction between tetramethylenediamine and ethoxyethylbromide. Few crystals suitable for a single-crystal structure determination recrystallized from an acetonitrile-methanol solution.

Refinement
All H atoms were located from the difference map and refined isotropically. Fig. 1. Left: The molecular structure of (I) showing 50% probability displacement ellipsoids and the atomic numbering [symmetry code: (i) -x + 1, y + 1/2, -z + 3/2]. Right: Spacefill presentation of location of eight bromides around a single dication. Six of the anions belong to the neighboring ion pairs.  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 > 2σ(F 2 ) is used only for calculating Rfactors(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.  (2)