organic compounds
2-Amino-5-methylpyridinium 2-carboxybenzoate
aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
*Correspondence e-mail: hkfun@usm.my
In the title salt, C6H9N2+·C8H5O4−, the hydrogen phthalate anion is essentially planar, with a maximum deviation of 0.011 (2) Å. In the the protonated N atom of the pyridine ring 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. In the hydrogen phthalate anion, there is a very strong, almost symmetric, intramolecular O—H⋯O hydrogen bond, generating an S(7) motif [O⋯O = 2.382 (3) Å]. Furthermore, these two molecular motif rings are connected by a bifurcated N—H⋯(O,O) hydrogen-bonded motif R12(4), forming a supramolecular ribbon along the b axis. The is further stabilized by π–π interactions between the cations and anions [centroid–centroid distance = 3.6999 (10) Å].
Related literature
For the ); Küppers (1981); Ermer (1981). For the crystal structures of hydrogen phthalates, see: Jessen (1990); Jin et al. (2003); Küppers (1978). For a description of the Cambridge Structural Database, see: Allen (2002). For hydrogen-bond motifs, see: Bernstein et al. (1995). For reference bond-length data, see: Allen et al. (1987).
of phthalic acid, see: Nowacki & Jaggi (1957Experimental
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/S160053681003000X/wn2402sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S160053681003000X/wn2402Isup2.hkl
A hot methanol solution (20 ml) of 2-amino-5-methylpyridine (27 mg, Aldrich) and phthalic acid (41 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.
Atoms H1N1, H2N2, H1N2 and H1O1 were located from a difference Fourier map and were refined freely [N—H= 0.90 (3) – 0.95 (2) Å and O—H = 1.16 (3) – 1.22 (3) Å]. The remaining hydrogen atoms were positioned geometrically [C—H = 0.93 or 0.96 Å] and were refined using a riding model, with Uiso(H) = 1.2 or 1.5Ueq(C). A rotating group model was used for the methyl group.
The
of phthalic acid (Nowacki & Jaggi, 1957; Küppers, 1981; Ermer, 1981) has been reported several times. Analysis of the structures archived in the Cambridge Structural Database (Version 5.28; Allen, 2002) shows that the hydrogen phthalate ions of phthalate salts occur in two different forms: (i) non-planar, where both the carboxyl (COOH) and the carboxylate (COO-) groups are twisted out of the plane of the benzene ring (Jessen, 1990; Jin et al., 2003), and (ii) planar, in which both the COOH and the COO- groups are coplanar with the benzene plane (Küppers, 1978). Since our aim is to study some interesting hydrogen-bonding interactions, the of the title compound is presented here.The
of the title compound (Fig 1), contains a protonated 2-amino-5-methylpyridinium cation and a hydrogen phthalate anion. In the 2-amino-5-methylpyridinium cation, a wide angle (122.45 (16)°) is subtended at the protonated N1 atom. The hydrogen phthalate anion is almost planar, with a maximum deviation of 0.011 (2) Å for atom C5. The bond lengths are normal (Allen et al., 1987).In the π–π interactions between the cations and anions [centroid-centroid distance = 3.6999 (10) Å ; symmetry code: -1/2+x, 1/2-y, 1/2+z].
(Fig. 2), the protonated N1 atom and the 2-amino group (N2) are hydrogen-bonded to the carboxylate oxygen atoms (O1 and O2) via a pair of N—H···O (Table 1) hydrogen bonds forming an R22(8) ring motif (Bernstein et al., 1995). In the hydrogen phthalate anion, there is a very strong intramolecular O—H···O hydrogen bond, generating an S(7) motif [O1···O3 = 2.382 (3) Å]. Furthermore, these two molecular motif rings are connected by a bifurcated hydrogen bonded motif R21(4), involving H1N2 of the 2-amino group and carboxyl atoms O3 and O4 to form a supramolecular ribbon along the b-axis. The is further stabilized byFor the
of phthalic acid, see: Nowacki & Jaggi (1957); Küppers (1981); Ermer (1981). For the crystal structures of hydrogen phthalates, see: Jessen (1990); Jin et al. (2003); Küppers (1978). For a description of the Cambridge Structural Database, see: Allen (2002). For hydrogen-bond motifs, see: Bernstein et al. (1995). For reference bond-length data, see: Allen et al. (1987).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. Hydrogen atoms are shown as spheres of arbitrary radius. A solid line indicates the intramolecular hydrogen bond. | |
Fig. 2. A view, down the a-axis, of supramolecular ribbons made up of cations and anions. The dashed lines indicate hydrogen bonds. |
C6H9N2+·C8H5O4− | F(000) = 576 |
Mr = 274.27 | Dx = 1.375 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 3124 reflections |
a = 11.3853 (2) Å | θ = 2.6–28.6° |
b = 8.8203 (2) Å | µ = 0.10 mm−1 |
c = 13.4617 (3) Å | T = 296 K |
β = 101.540 (2)° | Block, colourless |
V = 1324.52 (5) Å3 | 0.47 × 0.33 × 0.20 mm |
Z = 4 |
Bruker SMART APEXII CCD area-detector diffractometer | 3049 independent reflections |
Radiation source: fine-focus sealed tube | 2054 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.028 |
φ and ω scans | θmax = 27.5°, θmin = 2.6° |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | h = −14→14 |
Tmin = 0.953, Tmax = 0.980 | k = −11→11 |
12332 measured reflections | l = −17→12 |
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)] = 0.049 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.136 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.03 | w = 1/[σ2(Fo2) + (0.0585P)2 + 0.230P] where P = (Fo2 + 2Fc2)/3 |
3049 reflections | (Δ/σ)max < 0.001 |
197 parameters | Δρmax = 0.19 e Å−3 |
0 restraints | Δρmin = −0.14 e Å−3 |
C6H9N2+·C8H5O4− | V = 1324.52 (5) Å3 |
Mr = 274.27 | Z = 4 |
Monoclinic, P21/n | Mo Kα radiation |
a = 11.3853 (2) Å | µ = 0.10 mm−1 |
b = 8.8203 (2) Å | T = 296 K |
c = 13.4617 (3) Å | 0.47 × 0.33 × 0.20 mm |
β = 101.540 (2)° |
Bruker SMART APEXII CCD area-detector diffractometer | 3049 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | 2054 reflections with I > 2σ(I) |
Tmin = 0.953, Tmax = 0.980 | Rint = 0.028 |
12332 measured reflections |
R[F2 > 2σ(F2)] = 0.049 | 0 restraints |
wR(F2) = 0.136 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.03 | Δρmax = 0.19 e Å−3 |
3049 reflections | Δρmin = −0.14 e Å−3 |
197 parameters |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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 | 0.22365 (18) | −0.0844 (2) | 0.56803 (13) | 0.1122 (6) | |
O2 | 0.11271 (15) | −0.09799 (18) | 0.41687 (11) | 0.0907 (5) | |
O3 | 0.39091 (17) | 0.0516 (2) | 0.66089 (11) | 0.1042 (6) | |
O4 | 0.51382 (17) | 0.2270 (2) | 0.63733 (13) | 0.1129 (6) | |
C1 | 0.24378 (17) | 0.09471 (19) | 0.33146 (12) | 0.0560 (4) | |
H1A | 0.1762 | 0.0456 | 0.2956 | 0.067* | |
C2 | 0.30478 (17) | 0.1928 (2) | 0.28048 (13) | 0.0609 (5) | |
H2A | 0.2777 | 0.2107 | 0.2116 | 0.073* | |
C3 | 0.40493 (17) | 0.2635 (2) | 0.33145 (15) | 0.0689 (5) | |
H3A | 0.4481 | 0.3277 | 0.2973 | 0.083* | |
C4 | 0.44221 (17) | 0.2395 (2) | 0.43406 (16) | 0.0675 (5) | |
H4A | 0.5104 | 0.2894 | 0.4682 | 0.081* | |
C5 | 0.38123 (16) | 0.14284 (19) | 0.48854 (12) | 0.0547 (4) | |
C6 | 0.27973 (15) | 0.06614 (17) | 0.43513 (12) | 0.0508 (4) | |
C7 | 0.4338 (2) | 0.1418 (3) | 0.60205 (16) | 0.0719 (6) | |
C8 | 0.1997 (2) | −0.0461 (2) | 0.47582 (15) | 0.0644 (5) | |
N1 | 0.55034 (14) | 0.21351 (16) | 0.02651 (10) | 0.0539 (4) | |
N2 | 0.46340 (18) | 0.2514 (2) | −0.14144 (14) | 0.0712 (5) | |
C9 | 0.54553 (16) | 0.18327 (18) | −0.07217 (12) | 0.0532 (4) | |
C10 | 0.62974 (17) | 0.0798 (2) | −0.09620 (14) | 0.0611 (5) | |
H10A | 0.6290 | 0.0552 | −0.1635 | 0.073* | |
C11 | 0.71156 (17) | 0.0164 (2) | −0.02130 (14) | 0.0619 (5) | |
H11A | 0.7671 | −0.0511 | −0.0383 | 0.074* | |
C12 | 0.71554 (16) | 0.04912 (19) | 0.08173 (13) | 0.0573 (4) | |
C13 | 0.63244 (16) | 0.14845 (19) | 0.10155 (13) | 0.0581 (4) | |
H13A | 0.6316 | 0.1729 | 0.1686 | 0.070* | |
C14 | 0.80669 (19) | −0.0225 (3) | 0.16415 (16) | 0.0798 (6) | |
H14A | 0.7953 | 0.0133 | 0.2289 | 0.120* | |
H14B | 0.8858 | 0.0039 | 0.1553 | 0.120* | |
H14C | 0.7975 | −0.1307 | 0.1611 | 0.120* | |
H1N1 | 0.4931 (17) | 0.279 (2) | 0.0425 (14) | 0.067 (6)* | |
H2N2 | 0.404 (2) | 0.312 (3) | −0.1211 (17) | 0.086 (7)* | |
H1N2 | 0.466 (2) | 0.227 (3) | −0.206 (2) | 0.096 (8)* | |
H1O1 | 0.308 (2) | −0.022 (3) | 0.6119 (18) | 0.100 (7)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.1250 (15) | 0.1378 (15) | 0.0725 (10) | −0.0338 (12) | 0.0163 (10) | 0.0395 (10) |
O2 | 0.1126 (12) | 0.0943 (11) | 0.0705 (9) | −0.0427 (9) | 0.0308 (9) | −0.0029 (8) |
O3 | 0.1091 (13) | 0.1526 (16) | 0.0486 (8) | 0.0056 (12) | 0.0099 (9) | 0.0157 (10) |
O4 | 0.1112 (14) | 0.1306 (15) | 0.0794 (11) | −0.0074 (12) | −0.0228 (10) | −0.0167 (10) |
C1 | 0.0660 (11) | 0.0552 (9) | 0.0472 (9) | −0.0033 (8) | 0.0125 (8) | −0.0049 (7) |
C2 | 0.0717 (12) | 0.0679 (11) | 0.0459 (9) | 0.0020 (9) | 0.0182 (8) | 0.0024 (8) |
C3 | 0.0639 (12) | 0.0761 (12) | 0.0709 (12) | −0.0040 (10) | 0.0236 (10) | 0.0115 (10) |
C4 | 0.0502 (10) | 0.0771 (12) | 0.0731 (13) | −0.0024 (9) | 0.0072 (9) | −0.0031 (10) |
C5 | 0.0560 (10) | 0.0579 (9) | 0.0500 (9) | 0.0147 (8) | 0.0100 (8) | −0.0032 (7) |
C6 | 0.0617 (10) | 0.0460 (8) | 0.0478 (9) | 0.0080 (7) | 0.0185 (8) | −0.0019 (7) |
C7 | 0.0707 (13) | 0.0821 (14) | 0.0587 (11) | 0.0237 (11) | 0.0026 (10) | −0.0087 (10) |
C8 | 0.0841 (14) | 0.0567 (10) | 0.0575 (11) | −0.0010 (9) | 0.0265 (10) | 0.0015 (8) |
N1 | 0.0587 (9) | 0.0533 (8) | 0.0517 (8) | 0.0012 (7) | 0.0158 (7) | −0.0046 (6) |
N2 | 0.0868 (13) | 0.0727 (11) | 0.0517 (10) | 0.0110 (9) | 0.0079 (9) | −0.0033 (8) |
C9 | 0.0635 (11) | 0.0470 (8) | 0.0502 (9) | −0.0094 (8) | 0.0140 (8) | −0.0026 (7) |
C10 | 0.0753 (12) | 0.0588 (10) | 0.0532 (10) | −0.0047 (9) | 0.0225 (9) | −0.0102 (8) |
C11 | 0.0617 (11) | 0.0564 (10) | 0.0710 (11) | 0.0005 (8) | 0.0216 (9) | −0.0101 (9) |
C12 | 0.0543 (10) | 0.0569 (9) | 0.0613 (10) | −0.0037 (8) | 0.0133 (8) | −0.0035 (8) |
C13 | 0.0642 (11) | 0.0639 (10) | 0.0468 (9) | −0.0019 (9) | 0.0124 (8) | −0.0036 (8) |
C14 | 0.0699 (13) | 0.0880 (14) | 0.0781 (13) | 0.0120 (11) | 0.0064 (11) | −0.0013 (11) |
O1—C8 | 1.263 (2) | N1—C9 | 1.345 (2) |
O1—H1O1 | 1.16 (3) | N1—C13 | 1.359 (2) |
O2—C8 | 1.227 (2) | N1—H1N1 | 0.93 (2) |
O3—C7 | 1.286 (3) | N2—C9 | 1.325 (2) |
O3—H1O1 | 1.22 (3) | N2—H2N2 | 0.95 (2) |
O4—C7 | 1.203 (3) | N2—H1N2 | 0.90 (3) |
C1—C2 | 1.376 (2) | C9—C10 | 1.407 (3) |
C1—C6 | 1.396 (2) | C10—C11 | 1.350 (3) |
C1—H1A | 0.9300 | C10—H10A | 0.9300 |
C2—C3 | 1.359 (3) | C11—C12 | 1.409 (2) |
C2—H2A | 0.9300 | C11—H11A | 0.9300 |
C3—C4 | 1.378 (3) | C12—C13 | 1.355 (2) |
C3—H3A | 0.9300 | C12—C14 | 1.499 (3) |
C4—C5 | 1.397 (3) | C13—H13A | 0.9300 |
C4—H4A | 0.9300 | C14—H14A | 0.9600 |
C5—C6 | 1.406 (2) | C14—H14B | 0.9600 |
C5—C7 | 1.525 (3) | C14—H14C | 0.9600 |
C6—C8 | 1.520 (3) | ||
C8—O1—H1O1 | 111.6 (12) | C9—N1—H1N1 | 117.5 (11) |
C7—O3—H1O1 | 110.1 (11) | C13—N1—H1N1 | 120.1 (11) |
C2—C1—C6 | 122.40 (17) | C9—N2—H2N2 | 119.9 (13) |
C2—C1—H1A | 118.8 | C9—N2—H1N2 | 114.5 (15) |
C6—C1—H1A | 118.8 | H2N2—N2—H1N2 | 125 (2) |
C3—C2—C1 | 119.53 (17) | N2—C9—N1 | 119.25 (17) |
C3—C2—H2A | 120.2 | N2—C9—C10 | 123.33 (17) |
C1—C2—H2A | 120.2 | N1—C9—C10 | 117.42 (16) |
C2—C3—C4 | 119.66 (18) | C11—C10—C9 | 119.81 (16) |
C2—C3—H3A | 120.2 | C11—C10—H10A | 120.1 |
C4—C3—H3A | 120.2 | C9—C10—H10A | 120.1 |
C3—C4—C5 | 122.31 (18) | C10—C11—C12 | 122.15 (17) |
C3—C4—H4A | 118.8 | C10—C11—H11A | 118.9 |
C5—C4—H4A | 118.8 | C12—C11—H11A | 118.9 |
C4—C5—C6 | 117.98 (16) | C13—C12—C11 | 116.12 (16) |
C4—C5—C7 | 113.14 (18) | C13—C12—C14 | 122.30 (17) |
C6—C5—C7 | 128.82 (17) | C11—C12—C14 | 121.58 (17) |
C1—C6—C5 | 118.08 (16) | C12—C13—N1 | 122.04 (16) |
C1—C6—C8 | 113.62 (16) | C12—C13—H13A | 119.0 |
C5—C6—C8 | 128.29 (16) | N1—C13—H13A | 119.0 |
O4—C7—O3 | 119.6 (2) | C12—C14—H14A | 109.5 |
O4—C7—C5 | 120.4 (2) | C12—C14—H14B | 109.5 |
O3—C7—C5 | 120.0 (2) | H14A—C14—H14B | 109.5 |
O2—C8—O1 | 121.58 (19) | C12—C14—H14C | 109.5 |
O2—C8—C6 | 118.33 (16) | H14A—C14—H14C | 109.5 |
O1—C8—C6 | 120.09 (19) | H14B—C14—H14C | 109.5 |
C9—N1—C13 | 122.45 (16) | ||
C6—C1—C2—C3 | 1.1 (3) | C1—C6—C8—O2 | −1.1 (2) |
C1—C2—C3—C4 | −1.9 (3) | C5—C6—C8—O2 | 178.03 (17) |
C2—C3—C4—C5 | 0.7 (3) | C1—C6—C8—O1 | 178.51 (19) |
C3—C4—C5—C6 | 1.2 (3) | C5—C6—C8—O1 | −2.3 (3) |
C3—C4—C5—C7 | −176.18 (17) | C13—N1—C9—N2 | −179.69 (16) |
C2—C1—C6—C5 | 0.8 (3) | C13—N1—C9—C10 | 0.1 (2) |
C2—C1—C6—C8 | −179.89 (16) | N2—C9—C10—C11 | 179.23 (17) |
C4—C5—C6—C1 | −1.9 (2) | N1—C9—C10—C11 | −0.5 (3) |
C7—C5—C6—C1 | 175.00 (16) | C9—C10—C11—C12 | 0.6 (3) |
C4—C5—C6—C8 | 178.91 (16) | C10—C11—C12—C13 | −0.1 (3) |
C7—C5—C6—C8 | −4.1 (3) | C10—C11—C12—C14 | 179.80 (18) |
C4—C5—C7—O4 | 5.3 (3) | C11—C12—C13—N1 | −0.3 (3) |
C6—C5—C7—O4 | −171.79 (19) | C14—C12—C13—N1 | 179.74 (17) |
C4—C5—C7—O3 | −176.07 (19) | C9—N1—C13—C12 | 0.4 (3) |
C6—C5—C7—O3 | 6.9 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1N1···O2i | 0.928 (19) | 1.786 (19) | 2.713 (2) | 175.7 (17) |
N2—H2N2···O1i | 0.95 (2) | 1.97 (2) | 2.907 (3) | 173 (2) |
N2—H1N2···O3ii | 0.90 (3) | 2.39 (3) | 3.161 (2) | 143 (2) |
N2—H1N2···O4ii | 0.90 (3) | 2.28 (3) | 3.151 (3) | 162 (2) |
O1—H1O1···O3 | 1.16 (2) | 1.22 (2) | 2.382 (3) | 175 (2) |
Symmetry codes: (i) −x+1/2, y+1/2, −z+1/2; (ii) x, y, z−1. |
Experimental details
Crystal data | |
Chemical formula | C6H9N2+·C8H5O4− |
Mr | 274.27 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 296 |
a, b, c (Å) | 11.3853 (2), 8.8203 (2), 13.4617 (3) |
β (°) | 101.540 (2) |
V (Å3) | 1324.52 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.47 × 0.33 × 0.20 |
Data collection | |
Diffractometer | Bruker SMART APEXII CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 2009) |
Tmin, Tmax | 0.953, 0.980 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 12332, 3049, 2054 |
Rint | 0.028 |
(sin θ/λ)max (Å−1) | 0.650 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.049, 0.136, 1.03 |
No. of reflections | 3049 |
No. of parameters | 197 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.19, −0.14 |
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 | 0.928 (19) | 1.786 (19) | 2.713 (2) | 175.7 (17) |
N2—H2N2···O1i | 0.95 (2) | 1.97 (2) | 2.907 (3) | 173 (2) |
N2—H1N2···O3ii | 0.90 (3) | 2.39 (3) | 3.161 (2) | 143 (2) |
N2—H1N2···O4ii | 0.90 (3) | 2.28 (3) | 3.151 (3) | 162 (2) |
O1—H1O1···O3 | 1.16 (2) | 1.22 (2) | 2.382 (3) | 175 (2) |
Symmetry codes: (i) −x+1/2, y+1/2, −z+1/2; (ii) x, y, 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 Universiti Sains Malaysia for a post-doctoral research fellowship.
References
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The crystal structure of phthalic acid (Nowacki & Jaggi, 1957; Küppers, 1981; Ermer, 1981) has been reported several times. Analysis of the structures archived in the Cambridge Structural Database (Version 5.28; Allen, 2002) shows that the hydrogen phthalate ions of phthalate salts occur in two different forms: (i) non-planar, where both the carboxyl (COOH) and the carboxylate (COO-) groups are twisted out of the plane of the benzene ring (Jessen, 1990; Jin et al., 2003), and (ii) planar, in which both the COOH and the COO- groups are coplanar with the benzene plane (Küppers, 1978). Since our aim is to study some interesting hydrogen-bonding interactions, the crystal structure of the title compound is presented here.
The asymmetric unit of the title compound (Fig 1), contains a protonated 2-amino-5-methylpyridinium cation and a hydrogen phthalate anion. In the 2-amino-5-methylpyridinium cation, a wide angle (122.45 (16)°) is subtended at the protonated N1 atom. The hydrogen phthalate anion is almost planar, with a maximum deviation of 0.011 (2) Å for atom C5. The bond lengths are normal (Allen et al., 1987).
In the crystal structure (Fig. 2), the protonated N1 atom and the 2-amino group (N2) are hydrogen-bonded to the carboxylate oxygen atoms (O1 and O2) via a pair of N—H···O (Table 1) hydrogen bonds forming an R22(8) ring motif (Bernstein et al., 1995). In the hydrogen phthalate anion, there is a very strong intramolecular O—H···O hydrogen bond, generating an S(7) motif [O1···O3 = 2.382 (3) Å]. Furthermore, these two molecular motif rings are connected by a bifurcated hydrogen bonded motif R21(4), involving H1N2 of the 2-amino group and carboxyl atoms O3 and O4 to form a supramolecular ribbon along the b-axis. The crystal structure is further stabilized by π–π interactions between the cations and anions [centroid-centroid distance = 3.6999 (10) Å ; symmetry code: -1/2+x, 1/2-y, 1/2+z].