Crystal structure of 4-amino-1-(4-methylbenzyl)pyridinium bromide

The title molecular salt, C13H15N2 +·Br−, crystallized with two independent ion pairs (A and B) in the asymmetric unit. In the cations, the planes of the pyridine and benzene rings are inclined to one another by 79.32 (8) and 82.30 (10)° in ion pairs A and B, respectively. In the crystal, the anions and cations are connected by N—H⋯Br hydrogen bonds, forming a centrosymmetric tetramer-like unit enclosing an R 8 4(16) ring motif. These units are linked via C—H⋯Br hydrogen bonds, forming a three-dimensional network.


S1. Comment
Quarternary amine derivatives have been reported to possess antimicrobial properties (Thorsteinsson et al., 2003). The use of 4-aminopyridine derivatives are reported to be useful for the treatment of a peripheral nervous system demyelinating disease selected from Guillain-Barre syndrome diabetes mellitus and hereditary sensory-motor neuropathy.
Literature information revealed that the use of 4-aminopyridine had reduced chronic pain and spasticity in spinal cord injured patients (Hansebout et al., 1996). The crystal structures of a large number of pyridinium derivatives have been reported (Seethalakshmi et al., 2006;Sundar et al., 2006a,b,c) and their antimicrobial activities have also been reported (Ilangovan et al., 2012;Sundararaman et al., 2013).
The molecular structure of the two independent cations and anions of the title molecular salt is illustrated in Fig. 1. In the cations, the pyridine and benzene rings are inclined to one another by 79.32 (8)° in molecule A and by 82.30 (10)° in molecule B (Fig. 2). These values are similar to those observed in the crystal structures of some related compounds (Seethalakshmi et al., 2006;Sundar et al., 2006a,b,c). The overlap of the two cations in the title compound is illustrated in Fig. 2.
In the crystal, the cations and anions are linked via N-H···Br hydrogen bonds forming a tetramer-like unit enclosing an R 8 4 (16) ring motif (Table 1 and Fig. 3). These units are linked via C-H···Br hydrogen bonds forming a three-dimensional framework (Table 1 and Fig. 4).

S2. Experimental
A mixture of 4-methylbenzylbromide (0.1 mol) and 4-aminopyridine (0.1 mol) in dry acetone (50 ml) was stirred at room temperature for 2-12 h. The pale yellow solid that separated was filtered off, washed with toluene, dried under vacuum to give the stable title molecular salt. It was recrystallized from chloroform-acetone (1:1, v/v), giving thin yellow plate-like crystals.

S3. Refinement
The N-bound H atoms were located in a difference Fourier map and freely refined. The C-bound H atoms were included in calculated positions and treated as riding atoms: C-H = 0.93 -0.97 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms.
supporting information

Figure 1
The molecular structure of the two independent cations and anions of the title molecular salt, with atom labelling.
Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
A view of the molecular overlay of the two independent cations (cation A blue, cation B red).