4-Amino­pyridinium 2-hy­droxy­benzoate

Hoong-Kun Fun; Madhukar Hemamalini; Venkatachalam Rajakannan

doi:10.1107/S1600536810027042

. 2010 Jul 14;66(Pt 8):o2010–o2011. doi: 10.1107/S1600536810027042

4-Aminopyridinium 2-hydroxybenzoate

Hoong-Kun Fun ^a,^*,^‡, Madhukar Hemamalini ^a, Venkatachalam Rajakannan ^b

PMCID: PMC3007529 PMID: 21588323

Abstract

In the salicylate anion of the title salt, C₅H₇N₂ ⁺·C₇H₅O₃ ⁻, an intramolecular O—H⋯O hydrogen bond generating an S(6) ring motif is observed. In the crystal structure, the cations and anions are linked into a two-dimensional network parallel to the ab plane by N—H⋯O and C—H⋯O hydrogen bonds. The network contains R ₂ ²(7) and R ₁ ²(4) ring motifs. Weak π–π interactions between the benzene and pyridinium rings [centroid–centroid distance = 3.688 (1) Å] are also observed.

Related literature

For the biological activity of 4-aminopyridine, see: Schwid et al. (1997 ▶). For the crystal structure of 4-aminopyridine, see: Chao & Schempp (1977 ▶); Anderson et al. (2005 ▶). For related structures, see: Bhattacharya et al. (1994 ▶); Karle et al. (2003 ▶); Gellert & Hsu (1988 ▶); Hemamalini & Fun (2010 ▶). For hydrogen-bond motifs, see: Bernstein et al. (1995 ▶). For bond-length data, see: Allen et al. (1987 ▶). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986 ▶).

Experimental

Crystal data

C₅H₇N₂ ⁺·C₇H₅O₃ ⁻
M _r = 232.24
Orthorhombic,
a = 12.5801 (2) Å
b = 11.4157 (2) Å
c = 15.7560 (3) Å
V = 2262.73 (7) Å³
Z = 8
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 100 K
0.29 × 0.17 × 0.08 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ▶) T _min = 0.971, T _max = 0.992
15672 measured reflections
3010 independent reflections
2303 reflections with I > 2σ(I)
R _int = 0.057

Refinement

R[F ² > 2σ(F ²)] = 0.059
wR(F ²) = 0.118
S = 1.09
3010 reflections
170 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.37 e Å⁻³
Δρ_min = −0.26 e Å⁻³

Data collection: APEX2 (Bruker, 2009 ▶); cell refinement: SAINT (Bruker, 2009 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810027042/ci5130sup1.cif

e-66-o2010-sup1.cif^{(16.9KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810027042/ci5130Isup2.hkl

e-66-o2010-Isup2.hkl^{(147.8KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N1⋯O2ⁱ	0.96 (2)	2.48 (2)	3.1394 (19)	126 (2)
N1—H1N1⋯O3ⁱ	0.96 (2)	1.78 (2)	2.7296 (19)	172 (2)
N2—H1N2⋯O2	0.89 (2)	1.90 (2)	2.789 (2)	176 (2)
O1—H1O1⋯O3	0.97 (3)	1.61 (2)	2.5316 (18)	157 (2)
C11—H11A⋯O3ⁱⁱ	0.93	2.55	3.360 (2)	146
C12—H12A⋯O2ⁱ	0.93	2.56	3.164 (2)	123

Open in a new tab

Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

HKF and MH thank the Malaysian Government and Universiti Sains Malaysia for the Research University Golden Goose grant No. 1001/PFIZIK/811012. MH also thanks Universiti Sains Malaysia for a post-doctoral research fellowship.

supplementary crystallographic information

Comment

Aminopyridines are key intermediates for the synthesis of important pharmaceuticals and agrochemicals. Particularly, 4-aminopyridine (fampridine) is used in the treatment of neurological ailments, such as multiple sclerosis (MS), with tests showing that fampridine improves motor function in MS patients (Schwid et al., 1997). The crystal structure of 4-amino pyridine was first reported by Chao and Schempp (1977) and a redetermination was reported by Anderson et al. (2005). Salicylic acid (SA) is a common component in liquid scintillation systems. Salts of salicylic acid are good candidates for dry solid scintillators. Knowledge of these structural data is important to the development of a fundamental understanding of its scintillating properties, and more generally a predictive capability for tailoring materials to achieve desired scintillation properties. The present study has been carried out in order to study the hydrogen bonding patterns present in the crystal structure of 4-aminopyridinium salicylate, (I).

The asymmetric unit of (I) (Fig. 1) contains one 4-aminopyridinium cation and one salicylate anion, indicating that proton transfer occurred during the co-crystallisation experiment. Protonation leads to the widening of C8—N1—C12 angle in the pyridine ring to 120.26 (16)°, compared to 115.25 (13)° in neutal 4-aminopyridine (Anderson et al., 2005). This type of protonation has been observed in various 4-aminopyridine acid complexes (Bhattacharya et al., 1994; Karle et al., 2003). The bond lengths (Allen et al., 1987) and angles are within normal ranges.

In the crystal packing (Fig. 2), the protonated N atom and the hydrogen atom attached to atom C12 are hydrogen-bonded to the carboxylate oxygen atoms (O2 and O3) via N1—H1N1···O3 and C12—H12A···O2 hydrogen bonds, leading to the formation of an R²₂(7) ring motif (Bernstein et al., 1995). The carboxylate O atoms of the salicylate anion act as acceptors of bifurcated N1—H1N1···O2 and N1—H1N1···O3 hydrogen bonds with the protonated aromatic ring N atom of the 4-aminopyridinium cation, forming a ring with the graph-set notation R²₁(4). Furthermore, these two motifs are connected via N2—H1N2···O2 and C11—H11A···O3 (Table 1) hydrogen bonds, forming a two-dimensional network parallel to the ab-plane. There is an intramolecular O1—H1O1···O3 hydrogen bond in the salicylate anion, which generates an S(6) ring motif. This motif is also observed in the crystal structures of 2-aminopyridinium salicylate (Gellert & Hsu, 1988) and 2-amino-5-chloropyridinium salicylate (Hemamalini & Fun, 2010). The crystal structure is further stabilized by π–π interactions between the benzene ring at (x, y, z) and pyridinium ring at (3/2-x, 1/2+y, z) with a centroid-to-centroid distance of 3.688 (1) Å.

Experimental

A hot methanol solution (20 ml) of 4-aminopyridine (0.04705 g, Aldrich) and salicylic acid (0.0691 g, Merck) was warmed for 30 min over a water bath. The solution was cooled slowly and kept at room temperature. After a few days, colourless crystals were obtained.