organic compounds
2-Amino-5-methylpyridinium 2-carboxyacetate
aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
*Correspondence e-mail: hkfun@usm.my
In the title molecular salt, C6H9N2+·C3H3O4−, the cation is essentially planar, with a maximum deviation of 0.010 (3) Å. In the anion, an intramolecular O—H⋯O hydrogen bond generates an S(6) ring and results in a folded conformation. In the crystal, the protonated NH group and the 2-amino group of the cation are hydrogen bonded to the carboxylate O atoms of the anion via a pair of N—H⋯O hydrogen bonds, forming an R22(8) ring motif. Weak intermolecular C—H⋯O interactions help to further stabilize the crystal structure.
Related literature
For background to the chemistry of substituted pyridines, see: Pozharski et al. (1997); Katritzky et al. (1996). For related structures, see: Nahringbauer & Kvick (1977); Feng et al. (2005); Xuan et al. (2003); Jin et al. (2005); Hemamalini & Fun (2010a,b,c). For details of hydrogen bonding, see: Jeffrey & Saenger (1991); Jeffrey (1997); Scheiner (1997). For the conformation of the malonate ion, see: Djinović et al. (1990). 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 (Bruker, 2009); 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/S1600536810019239/hb5460sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810019239/hb5460Isup2.hkl
A hot methanol solution (20 ml) of 2-amino-5-methylpyridine (27 mg) and malonic acid (52 mg) were mixed and warmed over a heating magnetic stirrer for a few minutes. The resulting solution was allowed to cool slowly at room temperature and colourless blocks of (I) appeared after a few days.
All H atoms were located from a difference Fourier map and refined freely [C–H = 0.93 (4)–1.04 (4) Å and N–H = 0.89 (3)–0.97 (4) Å]. The hydrogen atom H1O3 was positioned geometrically and refined using a riding model.
Pyridine and its derivatives play an important role in heterocyclic chemistry (Pozharski et al., 1997; Katritzky et al., 1996). They are often involved in hydrogen-bond interactions (Jeffrey & Saenger, 1991; Jeffrey, 1997; Scheiner, 1997). The crystal structures of 2-amino-5-methylpyridine (Nahringbauer & Kvick, 1977), 2-amino-5-methylpyridinium phosphate (Feng et al., 2005), 2-amino-5-methylpyridinium 3-(4- hydroxy-3-methoxyphenyl)-2-propenoate monohydrate (Xuan et al., 2003) and 2-amino-5-methylpyridinium (2-amino-5- methylpyridine)trichlorozincate(II) (Jin et al., 2005) have been reported in the literature. We have recently reported the crystal structures of 2-amino-5-methylpyridinium 3-aminobenzoate (Hemamalini & Fun, 2010a), 2-amino-5-methylpyridinium 4-nitrobenzoate (Hemamalini & Fun, 2010b) and 2-amino-5-methylpyridinium nicotinate (Hemamalini & Fun, 2010c) from our laboratory. In order to study some interesting hydrogen bonding interactions, the synthesis and structure of the title salt is presented here.
The
(Fig. 1) contains one 2-amino-5-methylpyridinium cation and one hydrogen malonate anion. The proton transfer from the one of the carboxyl group oxygen atom (O2) to atom N1 of 2-amino-5-methylpyridine resulted in the widening of C1—N1—C5 angle of the pyridinium ring to 123.3 (2)°, compared to the corresponding angle of 117.4 (3)° in neutral 2-amino-5-methylpyridine (Nahringbauer & Kvick, 1977). The 2-amino-5-methylpyridinium cation is essentially planar, with a maximum deviation of 0.010 (3) Å for atom C4. The bond lengths and angles are normal (Allen et al., 1987).In the crystal packing (Fig. 2), the protonated N1 atom and the 2-amino group (N2) is hydrogen-bonded to the carboxylate oxygen atoms (O6 and O7) via a pair of intermolecular N1—H1N1···O2 and N2—H2N2···O1 hydrogen bonds forming a ring motif R22(8) (Bernstein et al., 1995). Atom O3 of the carboxyl group of the hydrogen malonate anions forms an intramolecular O3—H1O3···O1 hydrogen bond with the O atom of the carboxylate group (O1) [with graph-set notation S(6)], leading to a folded conformation. A similar intramolecular hydrogen bond has been observed in the crystal structures of benzylammonium hydrogen malonate and 4-picolinium hydrogen malonate (Djinović et al., 1990). The
is further stabilized by weak C2—H2A···O3 and C8—H8A···O2 (Table 1) hydrogen bonds.For background to the chemistry of substituted pyridines, see: Pozharski et al. (1997); Katritzky et al. (1996). For related structures, see: Nahringbauer & Kvick (1977); Feng et al. (2005); Xuan et al. (2003); Jin et al. (2005); Hemamalini & Fun (2010a,b,c). For details of hydrogen bonding, see: Jeffrey & Saenger (1991); Jeffrey (1997); Scheiner (1997). For the conformation of the malonate ion, see: Djinović et al. (1990). 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 (I). Displacement ellipsoids are drawn at the 50% probability level. | |
Fig. 2. The crystal packing of (I), showing hydrogen-bonded (dashed lines) networks. H atoms not involved in the hydrogen bond interactions are omitted for clarity. |
C6H9N2+·C3H3O4− | F(000) = 448 |
Mr = 212.21 | Dx = 1.426 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 3020 reflections |
a = 3.8082 (13) Å | θ = 2.4–29.9° |
b = 16.963 (5) Å | µ = 0.11 mm−1 |
c = 15.372 (5) Å | T = 100 K |
β = 95.436 (9)° | Block, colourless |
V = 988.6 (5) Å3 | 0.22 × 0.21 × 0.13 mm |
Z = 4 |
Bruker APEXII DUO CCD diffractometer | 2210 independent reflections |
Radiation source: fine-focus sealed tube | 1647 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.049 |
φ and ω scans | θmax = 27.5°, θmin = 1.8° |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | h = −3→4 |
Tmin = 0.975, Tmax = 0.986 | k = −22→21 |
8134 measured reflections | l = −19→19 |
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)] = 0.058 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.185 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.11 | w = 1/[σ2(Fo2) + (0.0826P)2 + 1.1878P] where P = (Fo2 + 2Fc2)/3 |
2210 reflections | (Δ/σ)max < 0.001 |
180 parameters | Δρmax = 0.41 e Å−3 |
0 restraints | Δρmin = −0.35 e Å−3 |
C6H9N2+·C3H3O4− | V = 988.6 (5) Å3 |
Mr = 212.21 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 3.8082 (13) Å | µ = 0.11 mm−1 |
b = 16.963 (5) Å | T = 100 K |
c = 15.372 (5) Å | 0.22 × 0.21 × 0.13 mm |
β = 95.436 (9)° |
Bruker APEXII DUO CCD diffractometer | 2210 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | 1647 reflections with I > 2σ(I) |
Tmin = 0.975, Tmax = 0.986 | Rint = 0.049 |
8134 measured reflections |
R[F2 > 2σ(F2)] = 0.058 | 0 restraints |
wR(F2) = 0.185 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.11 | Δρmax = 0.41 e Å−3 |
2210 reflections | Δρmin = −0.35 e Å−3 |
180 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 | ||
N1 | 0.9416 (6) | 0.73279 (11) | 0.44933 (13) | 0.0206 (5) | |
N2 | 1.1470 (7) | 0.75544 (13) | 0.31461 (14) | 0.0244 (5) | |
C1 | 1.0172 (7) | 0.78349 (13) | 0.38551 (16) | 0.0200 (5) | |
C2 | 0.9494 (7) | 0.86455 (14) | 0.39920 (17) | 0.0227 (6) | |
C3 | 0.8223 (7) | 0.88786 (13) | 0.47473 (17) | 0.0225 (5) | |
C4 | 0.7545 (7) | 0.83392 (14) | 0.54172 (16) | 0.0220 (5) | |
C5 | 0.8174 (7) | 0.75628 (14) | 0.52501 (16) | 0.0216 (5) | |
C6 | 0.6322 (9) | 0.86073 (17) | 0.62714 (19) | 0.0287 (6) | |
O1 | 0.3293 (5) | 0.58819 (10) | 0.30911 (11) | 0.0254 (5) | |
O2 | 0.0927 (5) | 0.58087 (10) | 0.43646 (11) | 0.0247 (5) | |
O3 | 0.5960 (6) | 0.46992 (10) | 0.24783 (12) | 0.0288 (5) | |
H1O3 | 0.5045 | 0.5236 | 0.2593 | 0.043* | |
O4 | 0.5733 (6) | 0.35450 (10) | 0.31494 (12) | 0.0305 (5) | |
C7 | 0.2547 (7) | 0.55182 (13) | 0.37706 (15) | 0.0201 (5) | |
C8 | 0.3717 (7) | 0.46644 (13) | 0.38965 (16) | 0.0197 (5) | |
C9 | 0.5161 (7) | 0.42551 (14) | 0.31344 (16) | 0.0221 (5) | |
H2A | 1.011 (8) | 0.8991 (17) | 0.3559 (18) | 0.019 (7)* | |
H3A | 0.762 (10) | 0.943 (2) | 0.485 (2) | 0.042 (9)* | |
H5A | 0.767 (7) | 0.7161 (15) | 0.5656 (16) | 0.011 (6)* | |
H6A | 0.817 (10) | 0.885 (2) | 0.661 (2) | 0.038 (9)* | |
H6B | 0.426 (11) | 0.899 (2) | 0.614 (2) | 0.044 (10)* | |
H6C | 0.532 (10) | 0.818 (2) | 0.660 (2) | 0.048 (10)* | |
H8A | 0.559 (9) | 0.4656 (18) | 0.4350 (19) | 0.025 (8)* | |
H8B | 0.173 (9) | 0.4314 (19) | 0.411 (2) | 0.033 (8)* | |
H1N1 | 1.008 (10) | 0.676 (2) | 0.438 (2) | 0.045 (10)* | |
H1N2 | 1.209 (8) | 0.7882 (19) | 0.273 (2) | 0.025 (8)* | |
H2N2 | 1.212 (10) | 0.700 (2) | 0.311 (2) | 0.038 (9)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0273 (12) | 0.0096 (9) | 0.0251 (10) | 0.0002 (8) | 0.0036 (8) | 0.0015 (7) |
N2 | 0.0371 (14) | 0.0120 (10) | 0.0251 (11) | 0.0017 (8) | 0.0072 (9) | 0.0023 (8) |
C1 | 0.0234 (14) | 0.0118 (11) | 0.0246 (12) | −0.0001 (9) | 0.0013 (9) | 0.0018 (8) |
C2 | 0.0273 (15) | 0.0105 (11) | 0.0301 (13) | −0.0003 (9) | 0.0019 (10) | 0.0023 (9) |
C3 | 0.0227 (14) | 0.0103 (10) | 0.0341 (13) | 0.0007 (9) | 0.0008 (10) | −0.0011 (9) |
C4 | 0.0222 (14) | 0.0165 (11) | 0.0273 (12) | 0.0008 (9) | 0.0022 (10) | −0.0030 (9) |
C5 | 0.0264 (14) | 0.0145 (11) | 0.0237 (11) | 0.0001 (9) | 0.0025 (10) | 0.0007 (9) |
C6 | 0.0320 (17) | 0.0244 (13) | 0.0302 (14) | 0.0001 (11) | 0.0052 (12) | −0.0058 (11) |
O1 | 0.0387 (12) | 0.0126 (8) | 0.0254 (9) | 0.0024 (7) | 0.0061 (8) | 0.0024 (7) |
O2 | 0.0374 (12) | 0.0108 (8) | 0.0268 (9) | 0.0044 (7) | 0.0082 (8) | 0.0007 (6) |
O3 | 0.0478 (13) | 0.0146 (9) | 0.0255 (9) | 0.0002 (8) | 0.0115 (8) | −0.0007 (7) |
O4 | 0.0496 (14) | 0.0108 (8) | 0.0326 (10) | 0.0014 (8) | 0.0112 (9) | −0.0030 (7) |
C7 | 0.0252 (14) | 0.0116 (10) | 0.0232 (12) | −0.0006 (9) | 0.0006 (9) | 0.0002 (8) |
C8 | 0.0264 (14) | 0.0110 (10) | 0.0221 (11) | 0.0014 (9) | 0.0040 (10) | 0.0007 (8) |
C9 | 0.0284 (15) | 0.0134 (11) | 0.0245 (12) | −0.0015 (9) | 0.0028 (10) | −0.0028 (9) |
N1—C1 | 1.356 (3) | C5—H5A | 0.96 (3) |
N1—C5 | 1.357 (3) | C6—H6A | 0.93 (4) |
N1—H1N1 | 1.02 (4) | C6—H6B | 1.03 (4) |
N2—C1 | 1.327 (3) | C6—H6C | 0.99 (4) |
N2—H1N2 | 0.89 (3) | O1—C7 | 1.268 (3) |
N2—H2N2 | 0.97 (4) | O2—C7 | 1.251 (3) |
C1—C2 | 1.419 (3) | O3—C9 | 1.317 (3) |
C2—C3 | 1.358 (4) | O3—H1O3 | 0.9974 |
C2—H2A | 0.93 (3) | O4—C9 | 1.224 (3) |
C3—C4 | 1.419 (4) | C7—C8 | 1.522 (3) |
C3—H3A | 0.97 (4) | C8—C9 | 1.510 (3) |
C4—C5 | 1.367 (3) | C8—H8A | 0.95 (3) |
C4—C6 | 1.505 (4) | C8—H8B | 1.04 (4) |
C1—N1—C5 | 123.3 (2) | C4—C5—H5A | 121.0 (15) |
C1—N1—H1N1 | 114 (2) | C4—C6—H6A | 110 (2) |
C5—N1—H1N1 | 122 (2) | C4—C6—H6B | 108 (2) |
C1—N2—H1N2 | 120 (2) | H6A—C6—H6B | 110 (3) |
C1—N2—H2N2 | 120.6 (19) | C4—C6—H6C | 113 (2) |
H1N2—N2—H2N2 | 118 (3) | H6A—C6—H6C | 110 (3) |
N2—C1—N1 | 119.2 (2) | H6B—C6—H6C | 105 (3) |
N2—C1—C2 | 123.8 (2) | C9—O3—H1O3 | 106.1 |
N1—C1—C2 | 117.0 (2) | O2—C7—O1 | 125.0 (2) |
C3—C2—C1 | 119.6 (2) | O2—C7—C8 | 116.2 (2) |
C3—C2—H2A | 124.1 (18) | O1—C7—C8 | 118.8 (2) |
C1—C2—H2A | 116.2 (18) | C9—C8—C7 | 117.6 (2) |
C2—C3—C4 | 122.4 (2) | C9—C8—H8A | 105.0 (18) |
C2—C3—H3A | 121 (2) | C7—C8—H8A | 107.3 (19) |
C4—C3—H3A | 116 (2) | C9—C8—H8B | 107.9 (18) |
C5—C4—C3 | 116.0 (2) | C7—C8—H8B | 111.9 (19) |
C5—C4—C6 | 122.0 (2) | H8A—C8—H8B | 106 (3) |
C3—C4—C6 | 122.1 (2) | O4—C9—O3 | 121.6 (2) |
N1—C5—C4 | 121.7 (2) | O4—C9—C8 | 121.0 (2) |
N1—C5—H5A | 117.3 (15) | O3—C9—C8 | 117.3 (2) |
C5—N1—C1—N2 | 178.1 (2) | C1—N1—C5—C4 | 0.9 (4) |
C5—N1—C1—C2 | −2.1 (4) | C3—C4—C5—N1 | 0.9 (4) |
N2—C1—C2—C3 | −178.8 (3) | C6—C4—C5—N1 | −177.2 (2) |
N1—C1—C2—C3 | 1.5 (4) | O2—C7—C8—C9 | 170.6 (2) |
C1—C2—C3—C4 | 0.2 (4) | O1—C7—C8—C9 | −10.1 (4) |
C2—C3—C4—C5 | −1.4 (4) | C7—C8—C9—O4 | −170.7 (3) |
C2—C3—C4—C6 | 176.7 (3) | C7—C8—C9—O3 | 13.0 (4) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H1O3···O1 | 1.00 | 1.53 | 2.475 (3) | 157 |
N1—H1N1···O2i | 1.02 (3) | 1.65 (3) | 2.652 (3) | 170 (3) |
N2—H1N2···O4ii | 0.90 (3) | 2.00 (3) | 2.886 (3) | 171 (3) |
N2—H2N2···O1i | 0.98 (3) | 1.95 (3) | 2.924 (3) | 177 (3) |
C2—H2A···O3ii | 0.93 (3) | 2.58 (3) | 3.470 (3) | 159 (2) |
C8—H8A···O2iii | 0.95 (3) | 2.41 (3) | 3.304 (3) | 158 (3) |
Symmetry codes: (i) x+1, y, z; (ii) −x+2, y+1/2, −z+1/2; (iii) −x+1, −y+1, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C6H9N2+·C3H3O4− |
Mr | 212.21 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 100 |
a, b, c (Å) | 3.8082 (13), 16.963 (5), 15.372 (5) |
β (°) | 95.436 (9) |
V (Å3) | 988.6 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.11 |
Crystal size (mm) | 0.22 × 0.21 × 0.13 |
Data collection | |
Diffractometer | Bruker APEXII DUO CCD |
Absorption correction | Multi-scan (SADABS; Bruker, 2009) |
Tmin, Tmax | 0.975, 0.986 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8134, 2210, 1647 |
Rint | 0.049 |
(sin θ/λ)max (Å−1) | 0.650 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.058, 0.185, 1.11 |
No. of reflections | 2210 |
No. of parameters | 180 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.41, −0.35 |
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 |
O3—H1O3···O1 | 1.00 | 1.53 | 2.475 (3) | 157 |
N1—H1N1···O2i | 1.02 (3) | 1.65 (3) | 2.652 (3) | 170 (3) |
N2—H1N2···O4ii | 0.90 (3) | 2.00 (3) | 2.886 (3) | 171 (3) |
N2—H2N2···O1i | 0.98 (3) | 1.95 (3) | 2.924 (3) | 177 (3) |
C2—H2A···O3ii | 0.93 (3) | 2.58 (3) | 3.470 (3) | 159 (2) |
C8—H8A···O2iii | 0.95 (3) | 2.41 (3) | 3.304 (3) | 158 (3) |
Symmetry codes: (i) x+1, y, z; (ii) −x+2, y+1/2, −z+1/2; (iii) −x+1, −y+1, −z+1. |
Footnotes
‡Thomson Reuters ResearcherID: A-3561-2009.
Acknowledgements
MH and HKF thank the Malaysian Government and Universiti Sains Malaysia for the Research University Golden Goose grant No. 1001/PFIZIK/811012. MH also thanks USM for a post-doctoral research fellowship.
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Pyridine and its derivatives play an important role in heterocyclic chemistry (Pozharski et al., 1997; Katritzky et al., 1996). They are often involved in hydrogen-bond interactions (Jeffrey & Saenger, 1991; Jeffrey, 1997; Scheiner, 1997). The crystal structures of 2-amino-5-methylpyridine (Nahringbauer & Kvick, 1977), 2-amino-5-methylpyridinium phosphate (Feng et al., 2005), 2-amino-5-methylpyridinium 3-(4- hydroxy-3-methoxyphenyl)-2-propenoate monohydrate (Xuan et al., 2003) and 2-amino-5-methylpyridinium (2-amino-5- methylpyridine)trichlorozincate(II) (Jin et al., 2005) have been reported in the literature. We have recently reported the crystal structures of 2-amino-5-methylpyridinium 3-aminobenzoate (Hemamalini & Fun, 2010a), 2-amino-5-methylpyridinium 4-nitrobenzoate (Hemamalini & Fun, 2010b) and 2-amino-5-methylpyridinium nicotinate (Hemamalini & Fun, 2010c) from our laboratory. In order to study some interesting hydrogen bonding interactions, the synthesis and structure of the title salt is presented here.
The asymmetric unit (Fig. 1) contains one 2-amino-5-methylpyridinium cation and one hydrogen malonate anion. The proton transfer from the one of the carboxyl group oxygen atom (O2) to atom N1 of 2-amino-5-methylpyridine resulted in the widening of C1—N1—C5 angle of the pyridinium ring to 123.3 (2)°, compared to the corresponding angle of 117.4 (3)° in neutral 2-amino-5-methylpyridine (Nahringbauer & Kvick, 1977). The 2-amino-5-methylpyridinium cation is essentially planar, with a maximum deviation of 0.010 (3) Å for atom C4. The bond lengths and angles are normal (Allen et al., 1987).
In the crystal packing (Fig. 2), the protonated N1 atom and the 2-amino group (N2) is hydrogen-bonded to the carboxylate oxygen atoms (O6 and O7) via a pair of intermolecular N1—H1N1···O2 and N2—H2N2···O1 hydrogen bonds forming a ring motif R22(8) (Bernstein et al., 1995). Atom O3 of the carboxyl group of the hydrogen malonate anions forms an intramolecular O3—H1O3···O1 hydrogen bond with the O atom of the carboxylate group (O1) [with graph-set notation S(6)], leading to a folded conformation. A similar intramolecular hydrogen bond has been observed in the crystal structures of benzylammonium hydrogen malonate and 4-picolinium hydrogen malonate (Djinović et al., 1990). The crystal structure is further stabilized by weak C2—H2A···O3 and C8—H8A···O2 (Table 1) hydrogen bonds.