organic compounds
2-Amino-5-chloropyridinium 6-oxo-1,6-dihydropyridine-2-carboxylate 0.85-hydrate
aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
*Correspondence e-mail: hkfun@usm.my
In the title salt, C5H6ClN2+·C6H4NO3−·0.85H2O, the pyridinium ring is planar, with a maximum deviation of 0.010 (2) Å. In the the cations, anions and water molecules are linked via N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds, forming a three-dimensional network.
Related literature
For applications of intermolecular interactions, see: Braga et al. (2002); Lam & Mak (2000). For related structures, see: Hemamalini & Fun (2010a,b,c,d,e,f); Sawada & Ohashi (1998). For hydrogen-bond motifs, see: Bernstein et al. (1995).
Experimental
Crystal data
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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/S1600536810032307/ci5153sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810032307/ci5153Isup2.hkl
A hot methanol solution (20 ml) of 2-amino-5-chloropyridine (64 mg, Aldrich) and 6-hydroxypicolinic acid (69 mg, Merck) were mixed and warmed over a heating magnetic stirrer hotplate for a few minutes. The resulting solution was allowed to cool slowly at room temperature and crystals of the title compound appeared after a few days.
The site occupancy of the water molecule was initially refined and then fixed at 0.85 in the final
The H-atoms were located in a difference Fourier map and refined freely [ranges of C—H = 0.89 (2)–0.95 (2) Å and N—H = 0.82 (3)–0.97 (2) Å]. The water H atoms were allowed to ride on the parent O atom.Intermolecular interaction analyses in crystalline systems are very important in supramolecular chemistry (Braga et al., 2002). These interactions are responsible for crystal packing, and through an understanding of such interactions we can comprehend collective properties and design new crystals with specific physical and chemical properties (Lam & Mak, 2000). We have been interested in hydrogen-bonded systems formed by 2-amino pyridines and
that generate molecular assemblies (Hemamalini & Fun, 2010a,b,c,d,e,f). In continuation of our studies of pyridinium derivatives, the determination of the title compound has been undertaken.The
(Fig. 1), contains one 2-amino-5-chloropyridinium cation, one 6-oxo-1,6-dihydropyridine-2-carboxylate anion and one water molecule with a refined site occupany of 0.85. The pyridinium ring is essentially planar, with a maximum deviation of 0.010 (2) Å for atom C5. In the 2-amino-5-chloropyridinium cation, a wider than normal angle [C1—N1—C2 = 122.55 (14)°] is subtended at the protonated N1 atom. The anion exists in the keto–enol of the -CONH moiety. Similar is also observed in the of 2-oxo-1,2-dihydropyridine-6-carboxylic acid (Sawada & Ohashi, 1998).In the crystal packing (Fig. 2), the protonated N1 atom and the 2-amino group (N2) are hydrogen-bonded to the carboxylate oxygen atoms (O2 and O3) via a pair of intermolecular N1—H1N1···O3 and N2—H2N2···O2 hydrogen bonds, forming an R22(8) ring motif (Bernstein et al., 1995). The ion pairs are further connected via O1W—H1W1···O3, O1W—H2W1···O1W, N2—H1N2···O1 and C4—H4···O1 (Table 1) hydrogen bonds, forming a three-dimensional network. The crystal of title compound is isomorphous with that of 2-amino-5-bromopyridinium 6-oxo-1,6-dihydropyridine-2-carboxylate monohydrate (Hemamalini & Fun, 2010f).
For applications of intermolecular interactions, see: Braga et al. (2002); Lam & Mak (2000). For related structures, see: Hemamalini & Fun (2010a,b,c,d,e,f); Sawada & Ohashi (1998). For hydrogen-bond motifs, see: Bernstein et al. (1995).
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. | |
Fig. 2. The crystal packing of the title compound, showing part of a hydrogen-bonded network. H atoms not involved in hydrogen bonding (dashed lines) have been omitted for clarity. |
C5H6ClN2+·C6H4NO3−·0.85H2O | F(000) = 586 |
Mr = 282.98 | Dx = 1.510 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 6806 reflections |
a = 3.8096 (1) Å | θ = 2.3–29.0° |
b = 15.6046 (3) Å | µ = 0.32 mm−1 |
c = 20.9370 (3) Å | T = 296 K |
V = 1244.65 (4) Å3 | Needle, green |
Z = 4 | 0.52 × 0.22 × 0.11 mm |
Bruker SMART APEXII CCD area-detector diffractometer | 3632 independent reflections |
Radiation source: fine-focus sealed tube | 3129 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.026 |
φ and ω scans | θmax = 30.1°, θmin = 1.6° |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | h = −4→5 |
Tmin = 0.851, Tmax = 0.966 | k = −21→21 |
15196 measured reflections | l = −29→29 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.036 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.113 | w = 1/[σ2(Fo2) + (0.0653P)2 + 0.0443P] where P = (Fo2 + 2Fc2)/3 |
S = 1.10 | (Δ/σ)max = 0.001 |
3632 reflections | Δρmax = 0.20 e Å−3 |
215 parameters | Δρmin = −0.17 e Å−3 |
0 restraints | Absolute structure: Flack (1983), with 1458 Fridel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: −0.04 (6) |
C5H6ClN2+·C6H4NO3−·0.85H2O | V = 1244.65 (4) Å3 |
Mr = 282.98 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 3.8096 (1) Å | µ = 0.32 mm−1 |
b = 15.6046 (3) Å | T = 296 K |
c = 20.9370 (3) Å | 0.52 × 0.22 × 0.11 mm |
Bruker SMART APEXII CCD area-detector diffractometer | 3632 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | 3129 reflections with I > 2σ(I) |
Tmin = 0.851, Tmax = 0.966 | Rint = 0.026 |
15196 measured reflections |
R[F2 > 2σ(F2)] = 0.036 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.113 | Δρmax = 0.20 e Å−3 |
S = 1.10 | Δρmin = −0.17 e Å−3 |
3632 reflections | Absolute structure: Flack (1983), with 1458 Fridel pairs |
215 parameters | Absolute structure parameter: −0.04 (6) |
0 restraints |
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 | Occ. (<1) | |
Cl1 | 0.29968 (15) | 0.97559 (3) | 1.16268 (2) | 0.04826 (15) | |
N1 | 0.0504 (4) | 0.98883 (9) | 0.97983 (7) | 0.0358 (3) | |
N2 | 0.1288 (6) | 0.90253 (11) | 0.89193 (7) | 0.0473 (4) | |
C1 | 0.0873 (5) | 1.00748 (10) | 1.04320 (8) | 0.0365 (4) | |
C2 | 0.1708 (5) | 0.91546 (9) | 0.95385 (8) | 0.0339 (3) | |
C3 | 0.3321 (6) | 0.85531 (10) | 0.99503 (8) | 0.0378 (4) | |
C4 | 0.3690 (5) | 0.87223 (11) | 1.05852 (9) | 0.0389 (4) | |
C5 | 0.2467 (5) | 0.95094 (10) | 1.08254 (7) | 0.0361 (4) | |
O1 | 0.8680 (5) | 0.75705 (8) | 0.15429 (5) | 0.0483 (4) | |
O2 | 0.6524 (5) | 0.96179 (8) | 0.31378 (6) | 0.0527 (4) | |
O3 | 0.8337 (5) | 0.90935 (8) | 0.40756 (6) | 0.0516 (4) | |
N3 | 0.8628 (4) | 0.82238 (9) | 0.25126 (6) | 0.0332 (3) | |
C6 | 0.9424 (5) | 0.75403 (10) | 0.21242 (8) | 0.0363 (4) | |
C7 | 1.1066 (5) | 0.68363 (11) | 0.24435 (9) | 0.0397 (4) | |
C8 | 1.1756 (6) | 0.68705 (11) | 0.30786 (9) | 0.0414 (4) | |
C9 | 1.0842 (6) | 0.75963 (12) | 0.34448 (8) | 0.0398 (4) | |
C10 | 0.9247 (5) | 0.82601 (10) | 0.31526 (8) | 0.0321 (3) | |
C11 | 0.7932 (6) | 0.90675 (10) | 0.34770 (7) | 0.0386 (4) | |
O1W | 0.5775 (11) | 0.18936 (16) | 1.01198 (10) | 0.1069 (12) | 0.85 |
H1W1 | 0.5888 | 0.1576 | 0.9790 | 0.101 (14)* | 0.85 |
H2W1 | 0.4401 | 0.2303 | 1.0216 | 0.109 (17)* | 0.85 |
H1 | −0.012 (6) | 1.0566 (13) | 1.0558 (9) | 0.040 (5)* | |
H3 | 0.416 (6) | 0.8069 (14) | 0.9779 (9) | 0.044 (6)* | |
H4 | 0.474 (6) | 0.8348 (12) | 1.0870 (8) | 0.032 (5)* | |
H8 | 1.274 (6) | 0.6427 (13) | 0.3299 (9) | 0.049 (6)* | |
H9 | 1.141 (9) | 0.7623 (15) | 0.3865 (11) | 0.065 (7)* | |
H7 | 1.155 (7) | 0.6344 (12) | 0.2193 (9) | 0.042 (5)* | |
H1N1 | −0.068 (6) | 1.0297 (13) | 0.9520 (10) | 0.046 (6)* | |
H1N2 | 0.222 (7) | 0.8578 (14) | 0.8740 (10) | 0.048 (6)* | |
H2N2 | 0.050 (7) | 0.9426 (17) | 0.8691 (11) | 0.057 (7)* | |
H1N3 | 0.771 (6) | 0.8649 (13) | 0.2351 (9) | 0.043 (6)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Cl1 | 0.0578 (3) | 0.0516 (2) | 0.0353 (2) | −0.0024 (2) | −0.0049 (2) | −0.00042 (17) |
N1 | 0.0431 (8) | 0.0311 (6) | 0.0331 (7) | 0.0030 (6) | 0.0011 (6) | 0.0030 (5) |
N2 | 0.0696 (13) | 0.0352 (7) | 0.0370 (7) | 0.0118 (8) | −0.0039 (8) | −0.0020 (6) |
C1 | 0.0429 (9) | 0.0308 (7) | 0.0358 (8) | 0.0003 (7) | 0.0029 (7) | 0.0006 (6) |
C2 | 0.0368 (8) | 0.0298 (7) | 0.0352 (7) | −0.0011 (7) | 0.0018 (8) | 0.0024 (6) |
C3 | 0.0400 (9) | 0.0302 (7) | 0.0432 (8) | 0.0033 (7) | −0.0002 (8) | 0.0020 (6) |
C4 | 0.0372 (9) | 0.0358 (8) | 0.0435 (9) | 0.0001 (8) | −0.0030 (8) | 0.0099 (7) |
C5 | 0.0370 (9) | 0.0383 (8) | 0.0329 (7) | −0.0048 (7) | −0.0002 (7) | 0.0029 (6) |
O1 | 0.0731 (10) | 0.0412 (6) | 0.0306 (5) | 0.0021 (7) | −0.0036 (7) | −0.0059 (5) |
O2 | 0.0771 (11) | 0.0396 (6) | 0.0414 (6) | 0.0175 (7) | −0.0040 (8) | −0.0052 (5) |
O3 | 0.0709 (10) | 0.0500 (7) | 0.0339 (6) | 0.0190 (8) | −0.0034 (8) | −0.0099 (5) |
N3 | 0.0434 (8) | 0.0265 (6) | 0.0297 (6) | 0.0026 (6) | −0.0020 (6) | 0.0002 (5) |
C6 | 0.0427 (9) | 0.0324 (7) | 0.0338 (7) | −0.0044 (7) | 0.0038 (8) | −0.0036 (6) |
C7 | 0.0440 (10) | 0.0321 (7) | 0.0429 (9) | 0.0048 (8) | 0.0060 (8) | −0.0045 (7) |
C8 | 0.0445 (10) | 0.0368 (8) | 0.0430 (9) | 0.0099 (8) | 0.0017 (9) | 0.0057 (7) |
C9 | 0.0447 (10) | 0.0421 (8) | 0.0325 (8) | 0.0040 (8) | −0.0020 (8) | 0.0005 (7) |
C10 | 0.0330 (8) | 0.0334 (7) | 0.0300 (7) | −0.0012 (7) | 0.0024 (7) | −0.0026 (6) |
C11 | 0.0466 (10) | 0.0357 (7) | 0.0335 (7) | 0.0030 (8) | −0.0001 (8) | −0.0054 (6) |
O1W | 0.187 (4) | 0.0767 (15) | 0.0574 (12) | 0.013 (2) | −0.0226 (18) | −0.0259 (11) |
Cl1—C5 | 1.7331 (16) | O2—C11 | 1.237 (2) |
N1—C2 | 1.348 (2) | O3—C11 | 1.2633 (18) |
N1—C1 | 1.365 (2) | N3—C10 | 1.362 (2) |
N1—H1N1 | 0.97 (2) | N3—C6 | 1.375 (2) |
N2—C2 | 1.322 (2) | N3—H1N3 | 0.82 (2) |
N2—H1N2 | 0.87 (2) | C6—C7 | 1.430 (3) |
N2—H2N2 | 0.84 (3) | C7—C8 | 1.356 (3) |
C1—C5 | 1.351 (2) | C7—H7 | 0.95 (2) |
C1—H1 | 0.90 (2) | C8—C9 | 1.411 (3) |
C2—C3 | 1.415 (2) | C8—H8 | 0.91 (2) |
C3—C4 | 1.363 (3) | C9—C10 | 1.348 (2) |
C3—H3 | 0.89 (2) | C9—H9 | 0.91 (2) |
C4—C5 | 1.407 (2) | C10—C11 | 1.516 (2) |
C4—H4 | 0.925 (19) | O1W—H1W1 | 0.85 |
O1—C6 | 1.2506 (19) | O1W—H2W1 | 0.85 |
C2—N1—C1 | 122.55 (14) | C10—N3—H1N3 | 116.4 (14) |
C2—N1—H1N1 | 118.2 (12) | C6—N3—H1N3 | 118.4 (14) |
C1—N1—H1N1 | 119.3 (12) | O1—C6—N3 | 119.75 (16) |
C2—N2—H1N2 | 119.8 (15) | O1—C6—C7 | 125.67 (15) |
C2—N2—H2N2 | 119.1 (16) | N3—C6—C7 | 114.58 (15) |
H1N2—N2—H2N2 | 120 (2) | C8—C7—C6 | 120.84 (16) |
C5—C1—N1 | 119.97 (16) | C8—C7—H7 | 122.4 (12) |
C5—C1—H1 | 124.8 (12) | C6—C7—H7 | 116.7 (12) |
N1—C1—H1 | 115.1 (12) | C7—C8—C9 | 121.09 (17) |
N2—C2—N1 | 118.97 (15) | C7—C8—H8 | 123.0 (13) |
N2—C2—C3 | 123.30 (16) | C9—C8—H8 | 115.8 (13) |
N1—C2—C3 | 117.72 (15) | C10—C9—C8 | 118.78 (15) |
C4—C3—C2 | 120.72 (16) | C10—C9—H9 | 120.8 (16) |
C4—C3—H3 | 121.2 (13) | C8—C9—H9 | 120.4 (17) |
C2—C3—H3 | 118.0 (13) | C9—C10—N3 | 119.51 (15) |
C3—C4—C5 | 118.93 (16) | C9—C10—C11 | 125.75 (15) |
C3—C4—H4 | 123.4 (11) | N3—C10—C11 | 114.73 (14) |
C5—C4—H4 | 117.6 (11) | O2—C11—O3 | 126.89 (15) |
C1—C5—C4 | 120.07 (16) | O2—C11—C10 | 117.57 (14) |
C1—C5—Cl1 | 119.85 (13) | O3—C11—C10 | 115.51 (15) |
C4—C5—Cl1 | 120.09 (13) | H1W1—O1W—H2W1 | 131.4 |
C10—N3—C6 | 125.17 (15) | ||
C2—N1—C1—C5 | −0.7 (3) | O1—C6—C7—C8 | −180.0 (2) |
C1—N1—C2—N2 | −179.18 (19) | N3—C6—C7—C8 | −0.4 (3) |
C1—N1—C2—C3 | 1.8 (3) | C6—C7—C8—C9 | 0.7 (3) |
N2—C2—C3—C4 | 179.8 (2) | C7—C8—C9—C10 | 0.3 (3) |
N1—C2—C3—C4 | −1.2 (3) | C8—C9—C10—N3 | −1.5 (3) |
C2—C3—C4—C5 | −0.5 (3) | C8—C9—C10—C11 | 176.86 (19) |
N1—C1—C5—C4 | −1.1 (3) | C6—N3—C10—C9 | 1.8 (3) |
N1—C1—C5—Cl1 | 178.92 (14) | C6—N3—C10—C11 | −176.69 (18) |
C3—C4—C5—C1 | 1.7 (3) | C9—C10—C11—O2 | 179.9 (2) |
C3—C4—C5—Cl1 | −178.37 (16) | N3—C10—C11—O2 | −1.7 (3) |
C10—N3—C6—O1 | 178.73 (18) | C9—C10—C11—O3 | −1.6 (3) |
C10—N3—C6—C7 | −0.8 (3) | N3—C10—C11—O3 | 176.80 (17) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1W1···O3i | 0.85 | 1.85 | 2.696 (3) | 174 |
O1W—H2W1···O1Wii | 0.85 | 1.99 | 2.732 (5) | 145 |
N1—H1N1···O3iii | 0.98 (2) | 1.67 (2) | 2.637 (2) | 170 (2) |
N2—H1N2···O1iv | 0.87 (2) | 1.97 (2) | 2.823 (2) | 168 (2) |
N2—H2N2···O2iii | 0.84 (3) | 2.04 (3) | 2.882 (2) | 179 (3) |
C4—H4···O1v | 0.93 (2) | 2.39 (2) | 3.296 (2) | 166 (2) |
Symmetry codes: (i) −x+3/2, −y+1, z+1/2; (ii) x−1/2, −y+1/2, −z+2; (iii) −x+1/2, −y+2, z+1/2; (iv) x−1/2, −y+3/2, −z+1; (v) x, y, z+1. |
Experimental details
Crystal data | |
Chemical formula | C5H6ClN2+·C6H4NO3−·0.85H2O |
Mr | 282.98 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 296 |
a, b, c (Å) | 3.8096 (1), 15.6046 (3), 20.9370 (3) |
V (Å3) | 1244.65 (4) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.32 |
Crystal size (mm) | 0.52 × 0.22 × 0.11 |
Data collection | |
Diffractometer | Bruker SMART APEXII CCD area-detector |
Absorption correction | Multi-scan (SADABS; Bruker, 2009) |
Tmin, Tmax | 0.851, 0.966 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 15196, 3632, 3129 |
Rint | 0.026 |
(sin θ/λ)max (Å−1) | 0.705 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.036, 0.113, 1.10 |
No. of reflections | 3632 |
No. of parameters | 215 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.20, −0.17 |
Absolute structure | Flack (1983), with 1458 Fridel pairs |
Absolute structure parameter | −0.04 (6) |
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 |
O1W—H1W1···O3i | 0.85 | 1.85 | 2.696 (3) | 174 |
O1W—H2W1···O1Wii | 0.85 | 1.99 | 2.732 (5) | 145 |
N1—H1N1···O3iii | 0.98 (2) | 1.67 (2) | 2.637 (2) | 170 (2) |
N2—H1N2···O1iv | 0.87 (2) | 1.97 (2) | 2.823 (2) | 168 (2) |
N2—H2N2···O2iii | 0.84 (3) | 2.04 (3) | 2.882 (2) | 179 (3) |
C4—H4···O1v | 0.93 (2) | 2.39 (2) | 3.296 (2) | 166 (2) |
Symmetry codes: (i) −x+3/2, −y+1, z+1/2; (ii) x−1/2, −y+1/2, −z+2; (iii) −x+1/2, −y+2, z+1/2; (iv) x−1/2, −y+3/2, −z+1; (v) x, y, z+1. |
Footnotes
‡Thomson Reuters ResearcherID: A-3561-2009.
Acknowledgements
The authors thank the Malaysian Government and Universiti Sains Malaysia for Research University Golden Goose grant No. 1001/PFIZIK/811012. MH also thanks Universiti Sains Malaysia for a postdoctoral research fellowship.
References
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Intermolecular interaction analyses in crystalline systems are very important in supramolecular chemistry (Braga et al., 2002). These interactions are responsible for crystal packing, and through an understanding of such interactions we can comprehend collective properties and design new crystals with specific physical and chemical properties (Lam & Mak, 2000). We have been interested in hydrogen-bonded systems formed by 2-amino pyridines and carboxylic acids that generate molecular assemblies (Hemamalini & Fun, 2010a,b,c,d,e,f). In continuation of our studies of pyridinium derivatives, the crystal structure determination of the title compound has been undertaken.
The asymmetric unit, (Fig. 1), contains one 2-amino-5-chloropyridinium cation, one 6-oxo-1,6-dihydropyridine-2-carboxylate anion and one water molecule with a refined site occupany of 0.85. The pyridinium ring is essentially planar, with a maximum deviation of 0.010 (2) Å for atom C5. In the 2-amino-5-chloropyridinium cation, a wider than normal angle [C1—N1—C2 = 122.55 (14)°] is subtended at the protonated N1 atom. The anion exists in the keto–enol tautomerism of the -CONH moiety. Similar tautomerism is also observed in the crystal structure of 2-oxo-1,2-dihydropyridine-6-carboxylic acid (Sawada & Ohashi, 1998).
In the crystal packing (Fig. 2), the protonated N1 atom and the 2-amino group (N2) are hydrogen-bonded to the carboxylate oxygen atoms (O2 and O3) via a pair of intermolecular N1—H1N1···O3 and N2—H2N2···O2 hydrogen bonds, forming an R22(8) ring motif (Bernstein et al., 1995). The ion pairs are further connected via O1W—H1W1···O3, O1W—H2W1···O1W, N2—H1N2···O1 and C4—H4···O1 (Table 1) hydrogen bonds, forming a three-dimensional network. The crystal of title compound is isomorphous with that of 2-amino-5-bromopyridinium 6-oxo-1,6-dihydropyridine-2-carboxylate monohydrate (Hemamalini & Fun, 2010f).