Crystal structure of 3-amino-1-propylpyridinium bromide

The title molecular salt crystallizes with two independent 3-aminopyridinium cations and two bromide anions in the asymmetric unit. In the crystal, the anions and cations are linked via N—H⋯Br and C—H⋯Br hydrogen bonds, forming chains propagating along [100].


Structural commentary
The asymmetric unit of the title salt, consists of two 3-aminopyrdinium cations and two bromide anions, as shown in Fig. 1. The geometrical parameters of the cation moiety are comparable with those of a related structure, 3-amino-1-(4nitrobenzyl)pyridinium bromide (Sundar et al., 2006). The molecular structure of the two cations are very similar with weighted and unit-weight r.m.s. fits of 0.089 and 0.081 Å , respectively, for ten fitted atoms (Fig. 2). The dihedral angle ISSN 1600-5368 between the mean planes of the pyridinium ring (N2/C1-C5) and the propyl group (N1/C6-C8) is 84.84 (2) in cation A, whereas the corresponding angle is 89.23 (2) in cation B.

Supramolecular features
The crystal structure of the title salt, is stabilized by a network of intermolecular N-HÁ Á ÁBr and C-HÁ Á ÁBr hydrogen bonds (Table 1 and Fig. 3). Anion Br2 is involved in five hydrogen bonds as an acceptor while anion Br1 is involved in only two hydrogen bonds. The dimerization of cation A mediates through two bromide anions with the aid of two N-HÁ Á ÁBr and C-HÁ Á ÁBr hydrogen bonds. As shown in Fig. 4, these interactions generate an R 2 4 (12) loop. Atom C16 (via H16A) forms a C-HÁ Á ÁBr i hydrogen bond with bromide anion Br2 [symmetry code: (i) x + 1, y, z]. The same Br2 anion acts as an acceptor for an N-HÁ Á ÁBr hydrogen bond with atom N4 of cation B. These interactions form a chain which runs parallel to the a axis (Fig. 5 The molecular structure of the title salt, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Structural superimposition of the non-H atoms of the pyridinium cations (green: cation A; violet: cation B).

Synthesis and crystallization
The title salt was prepared by dissolving 3-aminopyridine (0.94 g, 10 mM) in dried acetone (20 ml) and adding n-propyl bromide (1.48g, 12 mM). The reaction mixture was stirred at room temperature for 8 h. The title salt precipitated as a white solid, which was filtered and washed with cold acetone and dried in vacuum to afford the stable salt. It was recrystallized from an aqueous ethanol solution giving colourless prismatic crystals.

Refinement
The details of crystal data, data collection and structure refinement are summarized in Part of the crystal structure of the title salt, showing the formation of an R 4 2 (12) ring motif (see Table 1 for details; only the interacting atoms are labelled).