organic compounds
2-Amino-5-methylpyridinium 2-aminobenzoate
aSchool of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
*Correspondence e-mail: arazaki@usm.my
In the 2-aminobenzoate anion of the title salt, C6H9N2+·C7H6NO2−, an intramolecular N—H⋯O hydrogen bond is observed. The dihedral angle between the ring and the CO2 group is 8.41 (13)°. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxylate O atoms via a pair of N—H⋯O hydrogen bonds, forming an R22(8) ring motif. The ion pairs are further connected via N—H⋯O hydrogen bonds, resulting in a donor–donor–acceptor–acceptor (DDAA) array of quadruple hydrogen bonds. The also features a weak N—H⋯O hydrogen bond and a C—H⋯π interaction, resulting in a three-dimensional network.
Related literature
For background to the chemistry of substituted pyridines, see: Pozharski et al. (1997); Katritzky et al. (1996). For details of hydrogen bonding, see: Jeffrey (1997); Scheiner (1997). For related structures, see: Nahringbauer & Kvick (1977); Hemamalini & Fun (2010a,b); Bis & Zaworotko (2005); Thanigaimani et al. (2012). For hydrogen-bond motifs, see: Bernstein et al. (1995). For hydrogen-bonding patterns in organic salts, see: Baskar Raj et al. (2003). For bond-length data, see: Allen et al. (1987). For stability of the temperature controller used for 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
10.1107/S1600536812043243/is5202sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536812043243/is5202Isup2.hkl
Supporting information file. DOI: 10.1107/S1600536812043243/is5202Isup3.cml
Hot methanol solutions (20 ml) of 2-amino-5-methylpyridine (54 mg, Aldrich) and 2-aminobenzoic acid (34 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 (I) appeared after a few days.
N-bound H Atoms were located in a difference Fourier maps and refined freely [refined N—H distances 0.959 (18), 0.926 (18), 0.933 (17), 0.897 (17) and 0.923 (18) Å]. The remaining hydrogen atoms were positioned geometrically (C—H = 0.95–0.98 Å) and were refined using a riding model, with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(methyl C). A rotating group model was used for the methyl group. In the final
eleven outliers were omitted (-4 5 5, -1 4 5, 0 6 6, 4 6 3, 1 6 5, 0 1 1, 3 6 4, 1 4 4, -4 6 7, -1 6 6 and -3 6 7).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 molecular structure of the title compound with atom labels with 50% probability displacement ellipsoids. | |
Fig. 2. The crystal packing of the title compound. The H atoms not involved in the intermolecular interactions (dashed lines) have been omitted for clarity. |
C6H9N2+·C7H6NO2− | F(000) = 520 |
Mr = 245.28 | Dx = 1.358 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 4117 reflections |
a = 9.2394 (8) Å | θ = 2.6–32.5° |
b = 13.9200 (11) Å | µ = 0.09 mm−1 |
c = 12.1514 (8) Å | T = 100 K |
β = 129.850 (4)° | Block, pink |
V = 1199.82 (16) Å3 | 0.35 × 0.33 × 0.14 mm |
Z = 4 |
Bruker SMART APEXII DUO CCD area-detector diffractometer | 2707 independent reflections |
Radiation source: fine-focus sealed tube | 2361 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.031 |
ϕ and ω scans | θmax = 27.5°, θmin = 2.9° |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | h = −12→12 |
Tmin = 0.968, Tmax = 0.987 | k = −18→18 |
11650 measured reflections | l = −15→15 |
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)] = 0.037 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.101 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.07 | w = 1/[σ2(Fo2) + (0.0457P)2 + 0.4478P] where P = (Fo2 + 2Fc2)/3 |
2707 reflections | (Δ/σ)max < 0.001 |
184 parameters | Δρmax = 0.27 e Å−3 |
0 restraints | Δρmin = −0.24 e Å−3 |
C6H9N2+·C7H6NO2− | V = 1199.82 (16) Å3 |
Mr = 245.28 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 9.2394 (8) Å | µ = 0.09 mm−1 |
b = 13.9200 (11) Å | T = 100 K |
c = 12.1514 (8) Å | 0.35 × 0.33 × 0.14 mm |
β = 129.850 (4)° |
Bruker SMART APEXII DUO CCD area-detector diffractometer | 2707 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2009) | 2361 reflections with I > 2σ(I) |
Tmin = 0.968, Tmax = 0.987 | Rint = 0.031 |
11650 measured reflections |
R[F2 > 2σ(F2)] = 0.037 | 0 restraints |
wR(F2) = 0.101 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.07 | Δρmax = 0.27 e Å−3 |
2707 reflections | Δρmin = −0.24 e Å−3 |
184 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 e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(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 | −0.05463 (13) | 0.58465 (7) | 0.37647 (10) | 0.0151 (2) | |
N2 | −0.25399 (14) | 0.50164 (8) | 0.16340 (12) | 0.0204 (2) | |
C1 | 0.11839 (16) | 0.60745 (8) | 0.50265 (12) | 0.0151 (2) | |
H1A | 0.1274 | 0.6549 | 0.5629 | 0.018* | |
C2 | 0.27885 (15) | 0.56356 (8) | 0.54419 (12) | 0.0155 (2) | |
C3 | 0.25605 (16) | 0.49221 (8) | 0.45170 (13) | 0.0171 (2) | |
H3A | 0.3639 | 0.4586 | 0.4784 | 0.020* | |
C4 | 0.08252 (16) | 0.47011 (9) | 0.32426 (13) | 0.0177 (3) | |
H4A | 0.0711 | 0.4225 | 0.2631 | 0.021* | |
C5 | −0.07917 (16) | 0.51858 (8) | 0.28449 (12) | 0.0159 (2) | |
C6 | 0.47064 (16) | 0.59045 (9) | 0.68135 (13) | 0.0196 (3) | |
H6A | 0.4574 | 0.6181 | 0.7487 | 0.029* | |
H6B | 0.5289 | 0.6378 | 0.6607 | 0.029* | |
H6C | 0.5502 | 0.5330 | 0.7238 | 0.029* | |
O1 | 0.43909 (11) | 0.88549 (6) | 0.58761 (9) | 0.0185 (2) | |
O2 | 0.63811 (11) | 0.83318 (6) | 0.81350 (9) | 0.0196 (2) | |
N3 | 0.50078 (14) | 0.75894 (8) | 0.93299 (11) | 0.0194 (2) | |
C7 | 0.12951 (16) | 0.86387 (9) | 0.57403 (13) | 0.0182 (2) | |
H7A | 0.1169 | 0.8984 | 0.5008 | 0.022* | |
C8 | −0.03024 (16) | 0.84480 (9) | 0.55754 (13) | 0.0205 (3) | |
H8A | −0.1507 | 0.8658 | 0.4747 | 0.025* | |
C9 | −0.01034 (16) | 0.79390 (9) | 0.66560 (13) | 0.0194 (3) | |
H9A | −0.1190 | 0.7788 | 0.6550 | 0.023* | |
C10 | 0.16495 (16) | 0.76523 (9) | 0.78755 (13) | 0.0171 (2) | |
H10A | 0.1751 | 0.7310 | 0.8599 | 0.021* | |
C11 | 0.32976 (15) | 0.78581 (8) | 0.80692 (12) | 0.0149 (2) | |
C12 | 0.31006 (15) | 0.83401 (8) | 0.69541 (12) | 0.0147 (2) | |
C13 | 0.47372 (15) | 0.85226 (8) | 0.69945 (12) | 0.0150 (2) | |
H1 | −0.280 (2) | 0.4597 (12) | 0.0936 (19) | 0.032 (4)* | |
H2 | 0.500 (2) | 0.7164 (12) | 0.9882 (18) | 0.027 (4)* | |
H3 | 0.605 (2) | 0.7676 (13) | 0.9397 (18) | 0.034 (4)* | |
H4 | −0.165 (2) | 0.6175 (13) | 0.3487 (19) | 0.038 (5)* | |
H5 | −0.354 (2) | 0.5383 (12) | 0.1417 (18) | 0.031 (4)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0141 (5) | 0.0158 (5) | 0.0159 (5) | 0.0000 (4) | 0.0099 (4) | −0.0003 (4) |
N2 | 0.0149 (5) | 0.0239 (5) | 0.0183 (5) | −0.0009 (4) | 0.0088 (4) | −0.0060 (4) |
C1 | 0.0171 (5) | 0.0140 (5) | 0.0147 (5) | −0.0024 (4) | 0.0104 (5) | −0.0017 (4) |
C2 | 0.0150 (5) | 0.0156 (5) | 0.0153 (5) | −0.0013 (4) | 0.0094 (5) | 0.0012 (4) |
C3 | 0.0158 (5) | 0.0169 (5) | 0.0201 (6) | 0.0007 (4) | 0.0123 (5) | 0.0013 (5) |
C4 | 0.0190 (6) | 0.0167 (5) | 0.0191 (6) | −0.0009 (4) | 0.0130 (5) | −0.0028 (5) |
C5 | 0.0163 (5) | 0.0162 (5) | 0.0156 (5) | −0.0018 (4) | 0.0105 (5) | −0.0002 (4) |
C6 | 0.0156 (5) | 0.0200 (6) | 0.0184 (6) | −0.0007 (4) | 0.0087 (5) | −0.0018 (5) |
O1 | 0.0187 (4) | 0.0220 (4) | 0.0151 (4) | −0.0006 (3) | 0.0109 (4) | 0.0014 (3) |
O2 | 0.0132 (4) | 0.0241 (5) | 0.0180 (4) | −0.0006 (3) | 0.0084 (4) | 0.0046 (3) |
N3 | 0.0150 (5) | 0.0256 (5) | 0.0152 (5) | −0.0005 (4) | 0.0085 (4) | 0.0043 (4) |
C7 | 0.0179 (5) | 0.0189 (6) | 0.0146 (5) | 0.0009 (4) | 0.0090 (5) | 0.0006 (5) |
C8 | 0.0135 (5) | 0.0250 (6) | 0.0164 (6) | 0.0020 (4) | 0.0065 (5) | −0.0009 (5) |
C9 | 0.0148 (5) | 0.0219 (6) | 0.0216 (6) | −0.0031 (4) | 0.0117 (5) | −0.0053 (5) |
C10 | 0.0185 (5) | 0.0173 (6) | 0.0176 (6) | −0.0032 (4) | 0.0125 (5) | −0.0025 (4) |
C11 | 0.0147 (5) | 0.0138 (5) | 0.0136 (5) | −0.0010 (4) | 0.0079 (5) | −0.0027 (4) |
C12 | 0.0139 (5) | 0.0142 (5) | 0.0144 (5) | −0.0017 (4) | 0.0084 (5) | −0.0025 (4) |
C13 | 0.0156 (5) | 0.0124 (5) | 0.0153 (5) | −0.0010 (4) | 0.0091 (5) | −0.0013 (4) |
N1—C5 | 1.3498 (15) | O1—C13 | 1.2672 (14) |
N1—C1 | 1.3660 (14) | O2—C13 | 1.2651 (14) |
N1—H4 | 0.959 (18) | N3—C11 | 1.3717 (15) |
N2—C5 | 1.3356 (15) | N3—H2 | 0.897 (17) |
N2—H1 | 0.926 (18) | N3—H3 | 0.923 (18) |
N2—H5 | 0.933 (17) | C7—C8 | 1.3821 (17) |
C1—C2 | 1.3664 (16) | C7—C12 | 1.4064 (16) |
C1—H1A | 0.9500 | C7—H7A | 0.9500 |
C2—C3 | 1.4108 (17) | C8—C9 | 1.3966 (18) |
C2—C6 | 1.5077 (16) | C8—H8A | 0.9500 |
C3—C4 | 1.3716 (16) | C9—C10 | 1.3793 (16) |
C3—H3A | 0.9500 | C9—H9A | 0.9500 |
C4—C5 | 1.4125 (16) | C10—C11 | 1.4131 (16) |
C4—H4A | 0.9500 | C10—H10A | 0.9500 |
C6—H6A | 0.9800 | C11—C12 | 1.4153 (16) |
C6—H6B | 0.9800 | C12—C13 | 1.5029 (15) |
C6—H6C | 0.9800 | ||
C5—N1—C1 | 122.86 (10) | H6B—C6—H6C | 109.5 |
C5—N1—H4 | 117.1 (11) | C11—N3—H2 | 117.4 (10) |
C1—N1—H4 | 120.0 (11) | C11—N3—H3 | 117.0 (11) |
C5—N2—H1 | 122.7 (10) | H2—N3—H3 | 121.8 (15) |
C5—N2—H5 | 119.6 (10) | C8—C7—C12 | 122.28 (11) |
H1—N2—H5 | 117.2 (15) | C8—C7—H7A | 118.9 |
N1—C1—C2 | 121.54 (11) | C12—C7—H7A | 118.9 |
N1—C1—H1A | 119.2 | C7—C8—C9 | 118.44 (11) |
C2—C1—H1A | 119.2 | C7—C8—H8A | 120.8 |
C1—C2—C3 | 116.59 (10) | C9—C8—H8A | 120.8 |
C1—C2—C6 | 121.72 (11) | C10—C9—C8 | 120.90 (11) |
C3—C2—C6 | 121.68 (10) | C10—C9—H9A | 119.6 |
C4—C3—C2 | 121.81 (11) | C8—C9—H9A | 119.6 |
C4—C3—H3A | 119.1 | C9—C10—C11 | 121.22 (11) |
C2—C3—H3A | 119.1 | C9—C10—H10A | 119.4 |
C3—C4—C5 | 119.61 (11) | C11—C10—H10A | 119.4 |
C3—C4—H4A | 120.2 | N3—C11—C10 | 118.55 (11) |
C5—C4—H4A | 120.2 | N3—C11—C12 | 123.23 (10) |
N2—C5—N1 | 118.38 (10) | C10—C11—C12 | 118.22 (10) |
N2—C5—C4 | 124.05 (11) | C7—C12—C11 | 118.86 (10) |
N1—C5—C4 | 117.55 (10) | C7—C12—C13 | 118.47 (10) |
C2—C6—H6A | 109.5 | C11—C12—C13 | 122.65 (10) |
C2—C6—H6B | 109.5 | O2—C13—O1 | 123.53 (10) |
H6A—C6—H6B | 109.5 | O2—C13—C12 | 118.48 (10) |
C2—C6—H6C | 109.5 | O1—C13—C12 | 117.99 (10) |
H6A—C6—H6C | 109.5 | ||
C5—N1—C1—C2 | −0.49 (17) | C9—C10—C11—N3 | 177.35 (11) |
N1—C1—C2—C3 | −1.33 (17) | C9—C10—C11—C12 | −2.10 (17) |
N1—C1—C2—C6 | 178.25 (11) | C8—C7—C12—C11 | −2.35 (18) |
C1—C2—C3—C4 | 2.07 (17) | C8—C7—C12—C13 | 175.98 (11) |
C6—C2—C3—C4 | −177.52 (11) | N3—C11—C12—C7 | −176.04 (11) |
C2—C3—C4—C5 | −1.02 (18) | C10—C11—C12—C7 | 3.38 (16) |
C1—N1—C5—N2 | −179.68 (11) | N3—C11—C12—C13 | 5.71 (18) |
C1—N1—C5—C4 | 1.58 (16) | C10—C11—C12—C13 | −174.87 (10) |
C3—C4—C5—N2 | −179.47 (11) | C7—C12—C13—O2 | 173.86 (10) |
C3—C4—C5—N1 | −0.81 (17) | C11—C12—C13—O2 | −7.88 (17) |
C12—C7—C8—C9 | −0.13 (18) | C7—C12—C13—O1 | −6.58 (16) |
C7—C8—C9—C10 | 1.51 (18) | C11—C12—C13—O1 | 171.69 (10) |
C8—C9—C10—C11 | −0.38 (18) |
Cg1 is the centroid of the C7–C12 ring. |
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H3···O2 | 0.92 (2) | 1.97 (2) | 2.6734 (18) | 131.8 (15) |
N2—H1···O1i | 0.926 (18) | 1.982 (18) | 2.8561 (14) | 157 (2) |
N3—H2···O1ii | 0.897 (17) | 2.159 (18) | 3.0445 (14) | 168.7 (14) |
N1—H4···O2iii | 0.959 (18) | 1.723 (18) | 2.6776 (13) | 172.7 (17) |
N2—H5···O1iii | 0.933 (17) | 1.899 (18) | 2.8305 (14) | 176.8 (16) |
C1—H1A···Cg1 | 0.95 | 2.58 | 3.5094 (13) | 165 |
Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) x, −y+3/2, z+1/2; (iii) x−1, −y+3/2, z−1/2. |
Experimental details
Crystal data | |
Chemical formula | C6H9N2+·C7H6NO2− |
Mr | 245.28 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 100 |
a, b, c (Å) | 9.2394 (8), 13.9200 (11), 12.1514 (8) |
β (°) | 129.850 (4) |
V (Å3) | 1199.82 (16) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.35 × 0.33 × 0.14 |
Data collection | |
Diffractometer | Bruker SMART APEXII DUO CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 2009) |
Tmin, Tmax | 0.968, 0.987 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 11650, 2707, 2361 |
Rint | 0.031 |
(sin θ/λ)max (Å−1) | 0.649 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.037, 0.101, 1.07 |
No. of reflections | 2707 |
No. of parameters | 184 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.27, −0.24 |
Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).
Cg1 is the centroid of the C7–C12 ring. |
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H3···O2 | 0.92 (2) | 1.97 (2) | 2.6734 (18) | 131.8 (15) |
N2—H1···O1i | 0.926 (18) | 1.982 (18) | 2.8561 (14) | 157 (2) |
N3—H2···O1ii | 0.897 (17) | 2.159 (18) | 3.0445 (14) | 168.7 (14) |
N1—H4···O2iii | 0.959 (18) | 1.723 (18) | 2.6776 (13) | 172.7 (17) |
N2—H5···O1iii | 0.933 (17) | 1.899 (18) | 2.8305 (14) | 176.8 (16) |
C1—H1A···Cg1 | 0.95 | 2.58 | 3.5094 (13) | 165 |
Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) x, −y+3/2, z+1/2; (iii) x−1, −y+3/2, z−1/2. |
Footnotes
‡Thomson Reuters ResearcherID: A-5599-2009.
Acknowledgements
The authors thank the Malaysian Government and Universiti Sains Malaysia (USM) for the research facilities and Fundamental Research Grant Scheme (FRGS) No. 203/PFIZIK/6711171 to conduct this work. KT thanks The Academy of Sciences for the Developing World and USM for a TWAS–USM fellowship.
References
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Pyridine and its derivatives play an important role in heterocyclic chemistry (Pozharski et al., 1997; Katritzky et al., 1996). The are often involved in hydrogen-bond interactions (Jeffrey, 1997; Scheiner, 1997). The crystal structures of 2-amino-5-methylpyridine (Nahringbauer & Kvick, 1977), 2-amino-5-methylpyridinium 4-hydroxybenzoate (Hemamalini & Fun, 2010a), 2-amino-5-methylpyridinium 3-aminobenzoate (Hemamalini & Fun, 2010b) and 2-amino-5-methylpyridinium benzoate (Bis & Zaworotko, 2005) have been reported. In order to study some interesting hydrogen bonding interactions, the synthesis and structure of the title compound, (I), is presented here.
The asymmetric unit (Fig. 1) contains one 2-amino-5-methylpyridinium cation and one 2-aminobenzoate anion. In the 2-amino-5-methylpyridinium cation, a wider than normal angle [C1—N1—C5 = 122.86 (13)°] is subtended at the protonated N1 atom. The 2-amino-5-methylpyridinium cation is essentially planar, with a maximum deviation of 0.001 (1) Å for atom C2. The bond lengths (Allen et al., 1987) and angles are normal. In the crystal packing (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 intermolecular N1—H4···O2iii and N2—H5···O1iii hydrogen bonds (symmetry code in Table 1), forming an R22(8) (Bernstein et al., 1995) ring motif. These motifs are centrosymmetrically paired via N2—H1···O1i hydrogen bonds (symmetry code in Table 1), forming a complementary donor-donor-acceptor-acceptor (DDAA) array (Baskar Raj et al., 2003). These arrays are further connected via N3—H2···O1ii hydrogen bonds (symmetry code in Table 1), resulting a three-dimensional network. There is a typical intramolecular N3—H3···O2 hydrogen bond in the 2-aminobenzoate anion, (graph-set notation S6). The crystal structure is further stabilized by a weak C—H···π interaction (Table 1) involving the C7–C12 (centroid Cg1) ring.