2-Amino-5-methyl­pyridinium 2-carb­oxy­benzoate

In the title salt, C₆H₉N₂⁺·C₈H₅O₄⁻, the hydrogen phthalate anion is essentially planar, with a maximum deviation of 0.011 (2) Å. In the crystal structure, 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 crystal structure is further stabilized by π–π inter­actions between the cations and anions [centroid–centroid distance = 3.6999 (10) Å].

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.049
• wR factor = 0.136
• Data-to-parameter ratio = 15.5

checkCIF/PLATON results

No syntax errors found



Alert level C
SHFSU01_ALERT_2_C  Test not performed. _refine_ls_shift/su_max and
            _refine_ls_shift/esd_max not present.
            Absolute value of the parameter shift to su ratio given   0.001
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C7
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C8
PLAT369_ALERT_2_C Long   C(sp2)-C(sp2) Bond  C5     -   C7     ...       1.53 Ang.
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          1
PLAT042_ALERT_1_C Calc. and Reported MoietyFormula Strings  Differ          ?

Alert level G
PLAT128_ALERT_4_G Alternate Setting of Space-group P21/c   .......      P21/n
PLAT380_ALERT_4_G Check Incorrectly? Oriented X(sp2)-Methyl Moiety        C14
PLAT720_ALERT_4_G Number of Unusual/Non-Standard Labels ..........          4

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   6 ALERT level C = Check and explain
   3 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   4 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   3 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

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].

Related literature

For the crystal structure 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).

S2. Experimental

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.

S3. Refinement

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 U_iso(H) = 1.2 or 1.5U_eq(C). A rotating group model was used for the methyl group.

Computing details

Data collection: APEX2 (Bruker, 2009); cell refinement: 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).

Figures

	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.

2-Amino-5-methylpyridinium 2-carboxybenzoate

Crystal data

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) Å^3	0.47 × 0.33 × 0.20 mm
Z = 4

Data collection

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

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.049	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.136	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0585P)^2 + 0.230P] where P = (Fo^2 + 2Fc^2)/3
3049 reflections	(Δ/σ)max < 0.001
197 parameters	Δρmax = 0.19 e Å^−3
0 restraints	Δρmin = −0.14 e Å^−3

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	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)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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)

Geometric parameters (Å, º)

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)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N1···O2^i	0.928 (19)	1.786 (19)	2.713 (2)	175.7 (17)
N2—H2N2···O1^i	0.95 (2)	1.97 (2)	2.907 (3)	173 (2)
N2—H1N2···O3^ii	0.90 (3)	2.39 (3)	3.161 (2)	143 (2)
N2—H1N2···O4^ii	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.