A 1:1 proton transfer compound of 2-amino­benzoic acid with nitric acid

The asymmetric unit of the title compound, 2-carboxy­anilinium nitrate, C₇H₈NO₂⁺·NO₃⁻, consists of a 2-carboxy­anilinium cation protonated at the amino group and a nitrate anion. The carboxyl group of 2-carboxy­anilinium lies in the benzene-ring plane and a characteristic S(6)-type motif forms via an intra­molecular N—H...O hydrogen bond between the carbonyl O atom and the amino group. The structure exhibits strong classical O—H...O and three-centered N—H...O inter­actions. Aggregation of cations and anions through hydrogen bonds form infinite one-dimensional hydrogen-bonded ribbons extending along [10.

Key indicators

• Single-crystal X-ray study
• T = 294 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.049
• wR factor = 0.146
• Data-to-parameter ratio = 10.4

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT430_ALERT_2_B Short Inter D...A Contact  O4     ..  O4      ..       2.83 Ang.

Alert level C
PLAT094_ALERT_2_C Ratio of Maximum / Minimum Residual Density ....       2.15
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         N2
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          2
              N O3

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

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

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S1. Comment

2-aminobenzoic acid (anthralinic acid) is a useful derivatizing agent for carbohydrate analyses (He et al., 2003). Depending upon on the pH of a buffer, the 2-amionbenzoic acid can be either positively or negatively charged or neutral, since it has both a carboxyl group and an amino group. In the present study, 2-aminobenzoic acid was reacted with nitric acid and the structure of the product, (I), is reported.

The asymmetric unit of (I) consists of a 2-aminobenzoic acid cation protonated at the carboxylate group, and a nitrate anion. A strong O—H···O hydrogen bond links the 2-aminobenzoic acid cation to nitrate anion (Fig. 1). N—O bond lengths for the nitrate anion range from 1.233 (2) to 1.238 (2)°, and O—N—O bond angles ranges from 118.93 (18) to 120.89 (18)°.

The torsion angle C3—C2—C1—O1, -173.1 (2)°, clearly shows the coplanarity of the carboxyl group and the benzene ring and forms an intramolecular N—H···O hydrogen bond between the amino N atom and the carboxyl O atom thereby forming a characteristic S(6)-type motif (Bernstein et al., 1995).

N—H···O and O—H···O hydrogen bonds stabilize the crystal structure. All the oxygen atoms are participating in the hydrogen bonding network. The three 2-amino H atoms are involved in hydrogen bonding network with three-centre associations (Jeffrey & Saenger, 1991) with the acceptor atoms. The three H atoms of the amino group are involved in extensive N⁺—H···O^- hydrogen bonding interactions with O-atom acceptors of three different nitrate anions (Table 2). In addition, a glide-related cation-cation interaction is also observed through an N—H···O hydrogen bond. The structure can be considered as consisting of an infinite one-dimensional hydrogen-bonded ribbons extended diagonally as illustrated in Fig.2. Each ribbon consists of pairs of cations and anions, with the aromatic groups of the cations being parallel. Weak C—H···O interactions are also noticed in the crystal structure. A short interatomic contact is obseved between nitrate anions [O4···O4 = 2.381 Å] which is a consequence of the dense packing of the components by the hydrogen bonding.

Related literature

In all essential details, the molecular geometry of the title compound is in good agreement with those of similar structures (Brown & Ehrenberg, 1985; Takazawa et al., 1986). For information on the uses of the title compound, see: He et al. (2003). For details of hydrogen-bonding motifs, see: Bernstein et al. (1995) and Jeffrey & Saenger (1991).

S2. Experimental

2-aminobenzoic acid and nitric acid were mixed in a 1:1 stoichiometric ratio and dissolved in water. Crystal were obtained by slow evaporation.

S3. Refinement

All N-bound and O-bound H atoms were located in difference Fourier map and their positions and isotropic displacement parameters were refined. All other H atoms were positioned geometrically and treated as riding on their parent C atoms, with C—H distance = 0.93 Å, and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg & Putz, 2005) and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. Dashed lines indicate hydrogen bonds.
	Fig. 2. A view of the packing, showing the infinite one-dimensional hydrogen-bonded ribbons. Dashed lines indicate O—H···O and N—H···O hydrogen bonds. H atoms not involved in hydrogen bonding have been removed for clarity. Only atoms involved in hydrogen bonding are labelled. [symmetry code: (i) -x + 3/2, y - 1/2, -z + 3/2; (ii) x - 1/2, -y + 5/2, z - 1/; (iii) -x + 3/2, y - 3/2, -z + 3/2.].

2-carboxyanilinium nitrate

Crystal data

C7H8NO2^+·NO3^−	F(000) = 416
Mr = 200.15	Dx = 1.539 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 5597 reflections
a = 12.2368 (7) Å	θ = 2.6–27.9°
b = 5.0082 (3) Å	µ = 0.13 mm^−1
c = 14.8395 (9) Å	T = 294 K
β = 108.270 (1)°	Block, colorless
V = 863.58 (9) Å^3	0.20 × 0.15 × 0.09 mm
Z = 4

Data collection

Bruker SMART APEX CCD area-detector diffractometer	1415 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.042
Graphite monochromator	θmax = 25.0°, θmin = 2.9°
ω scans	h = −14→14
6687 measured reflections	k = −5→5
1498 independent reflections	l = −17→17

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.050	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.146	w = 1/[σ^2(Fo^2) + (0.0638P)^2 + 0.3928P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max < 0.001
1498 reflections	Δρmax = 0.44 e Å^−3
144 parameters	Δρmin = −0.21 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.209 (18)

Special details

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.

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

	x	y	z	Uiso*/Ueq
C1	0.63021 (16)	0.9765 (4)	0.84294 (13)	0.0392 (5)
C2	0.54112 (15)	0.7649 (3)	0.82574 (12)	0.0365 (5)
C3	0.51308 (15)	0.6048 (4)	0.74515 (12)	0.0374 (5)
C4	0.42748 (19)	0.4147 (4)	0.72904 (16)	0.0507 (6)
H4	0.4093	0.3094	0.6747	0.061*
C5	0.36898 (19)	0.3818 (5)	0.79429 (18)	0.0586 (6)
H5	0.3114	0.2535	0.7838	0.070*
C6	0.3953 (2)	0.5372 (5)	0.87449 (17)	0.0576 (6)
H6	0.3557	0.5141	0.9182	0.069*
C7	0.48004 (19)	0.7262 (4)	0.88997 (15)	0.0484 (6)
H7	0.4973	0.8309	0.9444	0.058*
N1	0.57349 (17)	0.6312 (5)	0.67506 (13)	0.0469 (5)
H1N	0.620 (3)	0.762 (8)	0.685 (2)	0.089 (11)*
H2N	0.523 (3)	0.667 (7)	0.617 (3)	0.087 (9)*
H3N	0.609 (3)	0.500 (7)	0.673 (2)	0.087 (11)*
O1	0.65438 (15)	1.0888 (3)	0.92666 (10)	0.0544 (5)
H1O	0.696 (3)	1.202 (6)	0.931 (2)	0.071 (9)*
O2	0.67464 (13)	1.0449 (3)	0.78371 (10)	0.0533 (5)
N2	0.85489 (14)	1.6057 (3)	0.98956 (11)	0.0415 (5)
O3	0.79176 (15)	1.4943 (3)	0.91758 (11)	0.0636 (5)
O4	0.92357 (15)	1.7801 (4)	0.98375 (13)	0.0725 (6)
O5	0.84897 (18)	1.5455 (4)	1.06845 (12)	0.0719 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0382 (10)	0.0427 (10)	0.0382 (10)	−0.0009 (8)	0.0140 (8)	−0.0070 (7)
C2	0.0353 (9)	0.0376 (10)	0.0371 (9)	0.0022 (7)	0.0119 (7)	−0.0006 (7)
C3	0.0333 (9)	0.0388 (10)	0.0378 (9)	0.0057 (7)	0.0080 (7)	−0.0016 (7)
C4	0.0470 (12)	0.0432 (11)	0.0532 (12)	−0.0026 (9)	0.0031 (9)	−0.0067 (9)
C5	0.0439 (12)	0.0529 (13)	0.0743 (15)	−0.0114 (10)	0.0119 (11)	0.0099 (11)
C6	0.0495 (12)	0.0646 (14)	0.0643 (14)	−0.0043 (10)	0.0259 (11)	0.0121 (11)
C7	0.0525 (12)	0.0538 (12)	0.0444 (11)	−0.0006 (9)	0.0231 (9)	−0.0013 (9)
N1	0.0460 (11)	0.0555 (12)	0.0405 (10)	0.0033 (9)	0.0156 (8)	−0.0127 (8)
O1	0.0615 (10)	0.0615 (10)	0.0441 (8)	−0.0206 (8)	0.0223 (7)	−0.0189 (7)
O2	0.0551 (9)	0.0644 (10)	0.0486 (8)	−0.0201 (7)	0.0282 (7)	−0.0137 (7)
N2	0.0404 (9)	0.0412 (9)	0.0440 (9)	−0.0065 (7)	0.0147 (7)	0.0037 (7)
O3	0.0621 (10)	0.0713 (11)	0.0534 (10)	−0.0141 (8)	0.0122 (8)	−0.0146 (8)
O4	0.0667 (11)	0.0738 (12)	0.0704 (11)	−0.0337 (9)	0.0122 (9)	0.0206 (9)
O5	0.0864 (14)	0.0809 (12)	0.0531 (10)	−0.0183 (10)	0.0287 (9)	0.0121 (8)

Geometric parameters (Å, º)

C1—O2	1.219 (2)	C6—C7	1.369 (3)
C1—O1	1.310 (2)	C6—H6	0.9300
C1—C2	1.484 (3)	C7—H7	0.9300
C2—C3	1.391 (3)	N1—H1N	0.85 (4)
C2—C7	1.397 (3)	N1—H2N	0.91 (4)
C3—C4	1.380 (3)	N1—H3N	0.79 (4)
C3—N1	1.459 (3)	O1—H1O	0.75 (3)
C4—C5	1.383 (3)	N2—O5	1.233 (2)
C4—H4	0.9300	N2—O4	1.234 (2)
C5—C6	1.373 (4)	N2—O3	1.238 (2)
C5—H5	0.9300
O2—C1—O1	122.96 (19)	C7—C6—H6	120.1
O2—C1—C2	123.13 (17)	C5—C6—H6	120.1
O1—C1—C2	113.88 (17)	C6—C7—C2	121.4 (2)
C3—C2—C7	117.79 (18)	C6—C7—H7	119.3
C3—C2—C1	121.98 (16)	C2—C7—H7	119.3
C7—C2—C1	120.21 (17)	C3—N1—H1N	114 (2)
C4—C3—C2	121.07 (18)	C3—N1—H2N	110 (2)
C4—C3—N1	117.77 (18)	H1N—N1—H2N	103 (3)
C2—C3—N1	121.16 (17)	C3—N1—H3N	111 (2)
C3—C4—C5	119.5 (2)	H1N—N1—H3N	107 (3)
C3—C4—H4	120.2	H2N—N1—H3N	110 (3)
C5—C4—H4	120.2	C1—O1—H1O	110 (2)
C6—C5—C4	120.5 (2)	O5—N2—O4	118.93 (18)
C6—C5—H5	119.8	O5—N2—O3	120.18 (17)
C4—C5—H5	119.8	O4—N2—O3	120.89 (18)
C7—C6—C5	119.8 (2)
O2—C1—C2—C3	8.8 (3)	C2—C3—C4—C5	−0.3 (3)
O1—C1—C2—C3	−173.12 (17)	N1—C3—C4—C5	179.4 (2)
O2—C1—C2—C7	−169.4 (2)	C3—C4—C5—C6	0.2 (3)
O1—C1—C2—C7	8.7 (3)	C4—C5—C6—C7	0.0 (4)
C7—C2—C3—C4	0.2 (3)	C5—C6—C7—C2	−0.1 (3)
C1—C2—C3—C4	−177.97 (17)	C3—C2—C7—C6	0.0 (3)
C7—C2—C3—N1	−179.47 (18)	C1—C2—C7—C6	178.24 (19)
C1—C2—C3—N1	2.3 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···O3	0.75 (3)	1.93 (3)	2.667 (2)	170 (3)
N1—H1N···O2	0.85 (4)	2.00 (4)	2.678 (3)	136 (3)
N1—H1N···O3^i	0.85 (4)	2.42 (3)	3.056 (3)	132 (3)
N1—H2N···O4^ii	0.91 (4)	1.99 (4)	2.891 (3)	173 (3)
N1—H2N···O5^ii	0.91 (4)	2.48 (4)	3.154 (3)	131 (3)
N1—H2N···N2^ii	0.91 (4)	2.58 (4)	3.443 (3)	159 (3)
N1—H3N···O4^iii	0.79 (4)	2.49 (3)	2.950 (2)	119 (3)
N1—H3N···O2^i	0.79 (4)	2.53 (4)	2.980 (2)	117 (3)
C4—H4···O5^iv	0.93	2.34	3.237 (3)	163
C6—H6···O5^v	0.93	2.59	3.378 (3)	143

Symmetry codes: (i) −x+3/2, y−1/2, −z+3/2; (ii) x−1/2, −y+5/2, z−1/2; (iii) −x+3/2, y−3/2, −z+3/2; (iv) x−1/2, −y+3/2, z−1/2; (v) −x+1, −y+2, −z+2.