3-(Ammoniomethyl)pyridinium dibromide

In the title salt, C6H10N2 2+·2Br−, the non-H atoms of the 3-methylpyridinium unit of the cation are almost coplanar (r.m.s. deviation = 0.0052 Å). In the crystal, the dications and Br anions are linked by a combination of six hydrogen bonds, viz. one Npy—H⋯Br, two C—H⋯Br and three H2N–H⋯Br, into supramolecular layers, parallel to the bc plane, composed of alternating R24(10) and R24(8) loops. Weak π–π interactions between cationic rings with centroid–centroid distances of 3.891 (2) Å are also observed.

In the title salt, C 6 H 10 N 2 2+ Á2Br À , the non-H atoms of the 3methylpyridinium unit of the cation are almost coplanar (r.m.s. deviation = 0.0052 Å ). In the crystal, the dications and Br anions are linked by a combination of six hydrogen bonds, viz. one N py -HÁ Á ÁBr, two C-HÁ Á ÁBr and three H 2 N-HÁ Á ÁBr, into supramolecular layers, parallel to the bc plane, composed of alternating R 2 4 (10) and R 2 4 (8) loops. Weakinteractions between cationic rings with centroid-centroid distances of 3.891 (2) Å are also observed.

sup-1
Acta Cryst.  (Desiraju, 1997). They exercise important effects on the organization and properties of many materials in areas such as biology (Hunter, 1994), crystal engineering (Allen et al., 1997, Dolling et al., 2001 and material science (Panunto et al., 1987, Robinson et al., 2000. We herein report the molecular structure of the salt, 3-(ammoniomethyl)pyridinium dibromide, along with it's supramolecular crystal structure.
The crystal packing involves extensive cation···anion interactions. These interactions assemble cations and anions into supramolecular layers parallel to the bc plane (Fig. 2) via N-H···Br and C-H···Br hydrogen bonding interactions of the types N py -H···Br, H 2 N-H···Br, and C-H···Br (Table 1). These layers are composed of alternating R 2 4 (10) [two bromide anions and two (py)C/N-H units of two cations] and R 2 4 (8) [two bromide anions and two ammonium groups via two H atoms each] graph set motifs (Bernstein et al., 1995). Interlayer interactions are established through the third hydrogen of the ammonium group with a bromide anion of a next layer (Fig. 2).
The cations also interact to some extent by offset face-to-face interactions along the a-axis, adding extra lattice stability. This is evident by the centroid separation distances C 1g ···C 1g (1 -x, 1 -y, 1 -z) of 3.891 (2) Å. The observed centroids separation distance is in accordance with those of calculated and the experimentally observed stacked (offset-face-to-face) interaction modes (Gould et al., 1985, Hunter & Sanders, 1990, Hunter, 1994, Singh & Thornton, 1990. The N-H···Br and C-H···Br hydrogen bonding and aryl···aryl interactions consolidate to from a three-dimensional network.

Experimental
The title compound was obtained unintentionally as the product of an attempted synthesis of a halo-stannate(II) organicinorganic hybrids, using slow evaporation of an ethanolic hot mixture of solution of SnCl 2 .2H 2 O (1 mmol) and Br 2 (l) and solution of 3-methylaminopyridine (1 mmol) with 2 ml of HBr at room temperature. Crystals were grown from ethanol upon cooling and slow evaporation (yield: 78%). A suitable block shaped crystal cut from a larger colorless crystal was epoxy mounted on a glass fiber and the data collected at room temperature.

Figure 1
Molecular configuration of the 3-(ammoniomethyl)pyridinium cation and the bromide anions in the asymmetric unit. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
Cation···anion interactions assembled supramolecular layers parallel to bc plane. N-H···Br and C-H···Br hydrogen bonding interactions appears as dotted lines. 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 > σ(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.