organic compounds
4-Aminopyridinium 2-hydroxybenzoate
aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia, and bBiomedical Structural Biology, School of Biological Sciences, Nanyang Technological University, Singapore 138673
*Correspondence e-mail: hkfun@usm.my
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 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 R22(7) and R12(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 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
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Refinement
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Data collection: APEX2 (Bruker, 2009); cell 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).
Supporting information
https://doi.org/10.1107/S1600536810027042/ci5130sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810027042/ci5130Isup2.hkl
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.
Atoms H1N1, H1N2, H2N2 and H1O1 were located from a difference Fourier map and were refined freely [N–H= 0.86 (2)–0.96 (2) Å and O–H = 0.97 (3) Å]. The remaining H atoms were positioned geometrically [C–H = 0.93 Å] and were refined using a riding model, with Uiso(H) = 1.2 Ueq(C).
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
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 of 4-aminopyridinium salicylate, (I).The
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 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.
is further stabilized byFor the biological activity of 4-aminopyridine, see: Schwid et al. (1997). For the
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).Data collection: APEX2 (Bruker, 2009); cell
SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).Fig. 1. The asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Dashed line indicates the intramolecular hydrogen bond. | |
Fig. 2. The crystal packing of the title compound, showing a hydrogen-bonded (dashed lines) 2D network. |
C5H7N2+·C7H5O3− | F(000) = 976 |
Mr = 232.24 | Dx = 1.363 Mg m−3 |
Orthorhombic, Pbca | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ac 2ab | Cell parameters from 2403 reflections |
a = 12.5801 (2) Å | θ = 2.6–28.5° |
b = 11.4157 (2) Å | µ = 0.10 mm−1 |
c = 15.7560 (3) Å | T = 100 K |
V = 2262.73 (7) Å3 | Plate, colourless |
Z = 8 | 0.29 × 0.17 × 0.08 mm |
Bruker SMART APEXII CCD area-detector diffractometer | 3010 independent reflections |
Radiation source: fine-focus sealed tube | 2303 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.057 |
φ and ω scans | θmax = 29.0°, θmin = 2.6° |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | h = −17→11 |
Tmin = 0.971, Tmax = 0.992 | k = −15→15 |
15672 measured reflections | l = −21→16 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.059 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.118 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.09 | w = 1/[σ2(Fo2) + (0.0323P)2 + 1.7134P] where P = (Fo2 + 2Fc2)/3 |
3010 reflections | (Δ/σ)max = 0.001 |
170 parameters | Δρmax = 0.37 e Å−3 |
0 restraints | Δρmin = −0.26 e Å−3 |
C5H7N2+·C7H5O3− | V = 2262.73 (7) Å3 |
Mr = 232.24 | Z = 8 |
Orthorhombic, Pbca | Mo Kα radiation |
a = 12.5801 (2) Å | µ = 0.10 mm−1 |
b = 11.4157 (2) Å | T = 100 K |
c = 15.7560 (3) Å | 0.29 × 0.17 × 0.08 mm |
Bruker SMART APEXII CCD area-detector diffractometer | 3010 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | 2303 reflections with I > 2σ(I) |
Tmin = 0.971, Tmax = 0.992 | Rint = 0.057 |
15672 measured reflections |
R[F2 > 2σ(F2)] = 0.059 | 0 restraints |
wR(F2) = 0.118 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.09 | Δρmax = 0.37 e Å−3 |
3010 reflections | Δρmin = −0.26 e Å−3 |
170 parameters |
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. |
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.93694 (11) | 0.70642 (11) | 0.39307 (9) | 0.0267 (3) | |
O2 | 1.08510 (10) | 0.38258 (10) | 0.38336 (8) | 0.0216 (3) | |
O3 | 1.08570 (10) | 0.56634 (10) | 0.43059 (8) | 0.0204 (3) | |
C1 | 0.89745 (14) | 0.62078 (15) | 0.34345 (11) | 0.0184 (4) | |
C2 | 0.80559 (14) | 0.64452 (17) | 0.29653 (12) | 0.0227 (4) | |
H2A | 0.7739 | 0.7180 | 0.2999 | 0.027* | |
C3 | 0.76181 (15) | 0.55938 (18) | 0.24519 (12) | 0.0255 (4) | |
H3A | 0.7003 | 0.5757 | 0.2146 | 0.031* | |
C4 | 0.80871 (15) | 0.44924 (17) | 0.23863 (12) | 0.0242 (4) | |
H4A | 0.7792 | 0.3923 | 0.2036 | 0.029* | |
C5 | 0.89968 (14) | 0.42548 (16) | 0.28476 (11) | 0.0203 (4) | |
H5A | 0.9312 | 0.3520 | 0.2802 | 0.024* | |
C6 | 0.94544 (13) | 0.50956 (15) | 0.33810 (11) | 0.0163 (3) | |
C7 | 1.04482 (14) | 0.48238 (15) | 0.38720 (11) | 0.0164 (3) | |
N1 | 0.76523 (12) | 0.02312 (13) | 0.49686 (9) | 0.0182 (3) | |
N2 | 1.02794 (13) | 0.14710 (14) | 0.37198 (11) | 0.0217 (3) | |
C8 | 0.82546 (14) | −0.05055 (15) | 0.45039 (11) | 0.0186 (4) | |
H8A | 0.8061 | −0.1290 | 0.4468 | 0.022* | |
C9 | 0.91367 (14) | −0.01310 (15) | 0.40865 (11) | 0.0178 (4) | |
H9A | 0.9543 | −0.0655 | 0.3772 | 0.021* | |
C10 | 0.94313 (13) | 0.10635 (14) | 0.41341 (11) | 0.0162 (3) | |
C11 | 0.87938 (14) | 0.18104 (15) | 0.46358 (11) | 0.0170 (4) | |
H11A | 0.8970 | 0.2598 | 0.4692 | 0.020* | |
C12 | 0.79224 (14) | 0.13756 (15) | 0.50369 (11) | 0.0186 (4) | |
H12A | 0.7504 | 0.1873 | 0.5364 | 0.022* | |
H1N1 | 0.7029 (19) | −0.003 (2) | 0.5260 (15) | 0.039 (7)* | |
H2N2 | 1.0665 (18) | 0.102 (2) | 0.3412 (15) | 0.032 (6)* | |
H1N2 | 1.0479 (19) | 0.222 (2) | 0.3735 (15) | 0.042 (7)* | |
H1O1 | 1.000 (2) | 0.669 (2) | 0.4166 (18) | 0.061 (9)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0301 (8) | 0.0199 (7) | 0.0302 (8) | 0.0066 (6) | −0.0086 (6) | −0.0064 (5) |
O2 | 0.0199 (6) | 0.0150 (6) | 0.0297 (7) | 0.0019 (5) | −0.0014 (6) | −0.0015 (5) |
O3 | 0.0196 (6) | 0.0173 (6) | 0.0242 (7) | −0.0002 (5) | −0.0051 (5) | −0.0032 (5) |
C1 | 0.0177 (8) | 0.0214 (9) | 0.0162 (9) | −0.0010 (7) | 0.0016 (7) | −0.0002 (7) |
C2 | 0.0191 (9) | 0.0280 (9) | 0.0210 (10) | 0.0050 (8) | 0.0032 (7) | 0.0042 (7) |
C3 | 0.0151 (9) | 0.0420 (11) | 0.0195 (9) | −0.0039 (8) | −0.0022 (7) | 0.0081 (8) |
C4 | 0.0243 (10) | 0.0305 (10) | 0.0179 (9) | −0.0106 (8) | −0.0027 (8) | 0.0005 (8) |
C5 | 0.0224 (9) | 0.0200 (8) | 0.0184 (9) | −0.0060 (7) | 0.0012 (7) | 0.0008 (7) |
C6 | 0.0151 (8) | 0.0193 (8) | 0.0146 (8) | −0.0035 (7) | 0.0016 (6) | 0.0002 (6) |
C7 | 0.0154 (8) | 0.0176 (8) | 0.0162 (8) | −0.0026 (7) | 0.0014 (7) | 0.0006 (6) |
N1 | 0.0153 (7) | 0.0189 (7) | 0.0205 (8) | −0.0016 (6) | 0.0007 (6) | 0.0020 (6) |
N2 | 0.0219 (8) | 0.0166 (8) | 0.0265 (9) | −0.0017 (7) | 0.0073 (7) | −0.0021 (6) |
C8 | 0.0201 (9) | 0.0148 (8) | 0.0209 (9) | −0.0010 (7) | −0.0027 (7) | 0.0003 (7) |
C9 | 0.0195 (8) | 0.0149 (8) | 0.0190 (9) | 0.0021 (7) | 0.0005 (7) | −0.0014 (6) |
C10 | 0.0158 (8) | 0.0174 (8) | 0.0155 (8) | 0.0003 (6) | −0.0020 (7) | 0.0014 (6) |
C11 | 0.0191 (9) | 0.0147 (8) | 0.0171 (9) | 0.0006 (7) | −0.0025 (7) | −0.0009 (6) |
C12 | 0.0200 (9) | 0.0183 (8) | 0.0175 (9) | 0.0036 (7) | −0.0009 (7) | −0.0016 (7) |
O1—C1 | 1.347 (2) | N1—C8 | 1.348 (2) |
O1—H1O1 | 0.97 (3) | N1—C12 | 1.354 (2) |
O2—C7 | 1.248 (2) | N1—H1N1 | 0.96 (2) |
O3—C7 | 1.285 (2) | N2—C10 | 1.335 (2) |
C1—C2 | 1.398 (3) | N2—H2N2 | 0.86 (2) |
C1—C6 | 1.408 (2) | N2—H1N2 | 0.89 (3) |
C2—C3 | 1.379 (3) | C8—C9 | 1.359 (2) |
C2—H2A | 0.93 | C8—H8A | 0.93 |
C3—C4 | 1.393 (3) | C9—C10 | 1.415 (2) |
C3—H3A | 0.93 | C9—H9A | 0.93 |
C4—C5 | 1.382 (3) | C10—C11 | 1.412 (2) |
C4—H4A | 0.93 | C11—C12 | 1.359 (2) |
C5—C6 | 1.400 (2) | C11—H11A | 0.93 |
C5—H5A | 0.93 | C12—H12A | 0.93 |
C6—C7 | 1.503 (2) | ||
C1—O1—H1O1 | 101.7 (16) | C8—N1—C12 | 120.26 (16) |
O1—C1—C2 | 118.11 (16) | C8—N1—H1N1 | 122.0 (14) |
O1—C1—C6 | 122.07 (16) | C12—N1—H1N1 | 117.7 (14) |
C2—C1—C6 | 119.82 (16) | C10—N2—H2N2 | 121.1 (15) |
C3—C2—C1 | 120.23 (17) | C10—N2—H1N2 | 123.1 (16) |
C3—C2—H2A | 119.9 | H2N2—N2—H1N2 | 116 (2) |
C1—C2—H2A | 119.9 | N1—C8—C9 | 121.71 (16) |
C2—C3—C4 | 120.70 (18) | N1—C8—H8A | 119.1 |
C2—C3—H3A | 119.7 | C9—C8—H8A | 119.1 |
C4—C3—H3A | 119.7 | C8—C9—C10 | 119.43 (16) |
C5—C4—C3 | 119.26 (17) | C8—C9—H9A | 120.3 |
C5—C4—H4A | 120.4 | C10—C9—H9A | 120.3 |
C3—C4—H4A | 120.4 | N2—C10—C11 | 121.15 (16) |
C4—C5—C6 | 121.44 (17) | N2—C10—C9 | 121.29 (16) |
C4—C5—H5A | 119.3 | C11—C10—C9 | 117.56 (16) |
C6—C5—H5A | 119.3 | C12—C11—C10 | 119.85 (16) |
C5—C6—C1 | 118.54 (16) | C12—C11—H11A | 120.1 |
C5—C6—C7 | 120.65 (16) | C10—C11—H11A | 120.1 |
C1—C6—C7 | 120.80 (15) | N1—C12—C11 | 121.17 (16) |
O2—C7—O3 | 122.97 (16) | N1—C12—H12A | 119.4 |
O2—C7—C6 | 120.08 (15) | C11—C12—H12A | 119.4 |
O3—C7—C6 | 116.94 (15) | ||
O1—C1—C2—C3 | −179.61 (17) | C1—C6—C7—O2 | 178.36 (16) |
C6—C1—C2—C3 | 0.1 (3) | C5—C6—C7—O3 | 175.74 (16) |
C1—C2—C3—C4 | −0.6 (3) | C1—C6—C7—O3 | −3.0 (2) |
C2—C3—C4—C5 | 0.5 (3) | C12—N1—C8—C9 | −0.6 (3) |
C3—C4—C5—C6 | 0.2 (3) | N1—C8—C9—C10 | −0.4 (3) |
C4—C5—C6—C1 | −0.7 (3) | C8—C9—C10—N2 | −178.64 (17) |
C4—C5—C6—C7 | −179.52 (16) | C8—C9—C10—C11 | 1.3 (2) |
O1—C1—C6—C5 | −179.75 (16) | N2—C10—C11—C12 | 178.68 (17) |
C2—C1—C6—C5 | 0.6 (2) | C9—C10—C11—C12 | −1.2 (2) |
O1—C1—C6—C7 | −0.9 (3) | C8—N1—C12—C11 | 0.6 (3) |
C2—C1—C6—C7 | 179.35 (16) | C10—C11—C12—N1 | 0.3 (3) |
C5—C6—C7—O2 | −2.9 (2) |
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 |
Symmetry codes: (i) x−1/2, −y+1/2, −z+1; (ii) −x+2, −y+1, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C5H7N2+·C7H5O3− |
Mr | 232.24 |
Crystal system, space group | Orthorhombic, Pbca |
Temperature (K) | 100 |
a, b, c (Å) | 12.5801 (2), 11.4157 (2), 15.7560 (3) |
V (Å3) | 2262.73 (7) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.29 × 0.17 × 0.08 |
Data collection | |
Diffractometer | Bruker SMART APEXII CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 2009) |
Tmin, Tmax | 0.971, 0.992 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 15672, 3010, 2303 |
Rint | 0.057 |
(sin θ/λ)max (Å−1) | 0.682 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.059, 0.118, 1.09 |
No. of reflections | 3010 |
No. of parameters | 170 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.37, −0.26 |
Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).
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 |
Symmetry codes: (i) x−1/2, −y+1/2, −z+1; (ii) −x+2, −y+1, −z+1. |
Footnotes
‡Thomson Reuters ResearcherID: A-3561-2009.
Acknowledgements
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.
References
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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.