3-Carboxy­anilinium 3-carb­oxy-4-hydroxy­benzene­sulfonate: the 1:1 proton-transfer compound of 5-sulfosalicylic acid with 3-amino­benzoic acid

The crystal structure of the anhydrous 1:1 proton-transfer compound of 5-sulfosalicylic acid (3-carb­oxy-4-hydroxy­benzene­sulfonic acid) with 3-amino­benzoic acid, C₇H₈NO₂⁺·C₇H₅O₆S⁻, shows heteromeric cyclic R₂²(8) carboxylic acid dimers formed through hydrogen-bonding inter­actions between the cation and anion species. Aminium–sulfonate N—H...O inter­actions link these dimers into zigzag chains and also give inter­chain associations. Cation–anion π–π ring inter­actions are also present, resulting in a three-dimensional layered polymer structure.

Key indicators

• Single-crystal X-ray study
• T = 297 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.045
• wR factor = 0.158
• Data-to-parameter ratio = 10.7

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S1. Comment

The structures of a number of 1:1 proton-transfer compounds of 3-carboxy-4-hydroxybenzenesulfonic acid (5-sulfosalicylic acid, 5-SSA) with aniline-type Lewis bases have been reported. These include compounds with aniline (Bakasova et al., 1991), the 4-X-substituted anilines (X = F, Cl, Br) (Smith et al., 2005a), 4-aminobenzoic acid (PABA) (Smith et al., 2005b) and 1,4-phenylenediamine (in which 5-SSA is dianionic) (Smith et al., 2005). Although the isomeric aminobenzoic acids are quite strong for organic acids (pK_a1 range 2.1–3.1), in the presence of stronger acids such as the nitrobenzoic acids or sulfonic acids, e.g. 5-SSA, protonation of the amine substituent will occur (for 3-aminobenzoic acid, pK_a2 = 4.7). The resultant aminium group is particularly effective in giving up to six hydrogen-bonding interactions usually with available O-atom acceptors, resulting in formation of good crystalline materials. In these crystals, it is unusual that water molecules of solvation are incorporated, contrasting with those compounds of 5-SSA with heteroaromatic Lewis bases where water is often found, acting in a proton donor–acceptor capacity. Furthermore, with these hydrates, direct N⁺—H···O(water) rather than N⁺—H···O(sulfonate) associations are more commonly found (Haynes et al., 2004). 3-Aminobenzoic acid (MABA) is less effective than PABA for the promotion of linear hydrogen-bonding extensions so that the structures of the proton-transfer compounds of MABA with organic acids are fewer. They include 1:1 compounds with 3,5-dinitrobenzoic acid (Lynch et al., 1994), 3,5-dinitrosalicylic acid (Smith et al., 1995a) and pyrazine-2,3-dicarboxylic acid (a dihydrate) (Smith et al., 1995b). Compounds in which MABA does not give proton transfer are the adducts with 2-aminopyrimidine (Smith et al., 1995) and 2-aminobenzothiazole (Lynch et al., 1998).

The structure of the anhydrous 1:1 proton-transfer compound formed from the reaction of 5-SSA with MABA in 50% aqueous ethanol, viz. 3-carboxyanilinium 5-sulfonatosalicylate, (I) (Fig. 1), has been determined and is reported here. In (I), the MABA cation and 5-SSA anion species form hydrogen-bonded heterodimers through symmetric cyclic R₂²(8) carboxylic acid interactions [O···O = 2.677 (4) and 2.679 (4) Å]. This is in contrast with the structure of the isomeric compound with PABA (Smith et al., 2005b), where both the PABA cations and the 5-SSA anions are involved in homomolecular R₂²(8) associations. In (I), the dimers form zigzag chains through head-to-tail N⁺—H···O(sulfonate) interactions [N31···O53^iv = 2.921 (5) Å; symmetry code: (iv) −1/2 + x, 1/2 − y, 1/2 + z], which run along the b axial direction (Figs. 2 and 3). The chains so formed are linked along the other two axial directions by similar N—H···O interactions (Table 1), giving a three-dimensional layered structure. In addition, there are some cation–anion π–π ring stacking interactions between the stacks which form down the a axial direction [ring centroid separation = 3.73 (1) Å and interplanar dihedral angle = 2.4 (1) °].

Structurally, the 5-SSA anion molecules are similar to those in previously reported compounds. The carboxylic acid group is essentially coplanar with the benzene ring [C2–C1–C7–O72 = 177.7 (4)°] because of the intramolecular O—H(phenol)···O(carboxyl) hydrogen bond [O···O = 2.598 (5) Å]. The carboxylic acid group of the MABA cation molecule shows significant deviation from coplanarity with the benzene ring [C21—C11—C71—O711 = 167.1 (4)°] as is observed in the compound with 3,5-dinitrosalicylic acid (−153°; Smith et al., 1995a) but different from the equivalent angle in the planar parent acid (−178°; Voogd et al., 1980).

S2. Experimental

The title compound was synthesized by heating 1 mmol quantities of 3-carboxy-4-hydroxybenzenesulfonic acid (5-sulfosalicylic acid) and 3-aminobenzoic acid in 50% ethanol–water (50 ml) for 10 min under reflux. After concentration to ca 30 ml, partial room temperature evaporation of the hot-filtered solution gave pale-brown crystal prisms of (I) (m.p. 541 K).

S3. Refinement

H atoms potentially involved in hydrogen-bonding interactions were located by difference methods and their positional and isotropic displacement parameters were refined. Other H atoms were included in the refinement in calculated positions (C—H = 0.96 Å) using a riding-model approximation, with U_eq values fixed at 1.2U_eq(C). A 15.8% decay in the diffraction intensities during data collection was allowed for using a linear correction.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1999); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN for Windows (Molecular Structure Corporation, 1999); program(s) used to solve structure: SIR92 (Altomare, 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: PLATON.

Figures

	Fig. 1. The molecular configuration and atom-numbering scheme for the MABA cation and 5-SSA anion in (I). Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. Perspective view of the packing of (I) in the unit cell, viewed down the approximate c-cell direction, showing hydrogen-bonding associations as dashed lines. [Symmetry code: (v) 1/2 + x, 1/2 − y, 1/2 + z; for other codes, see Table 1].
	Fig. 3. Perspective view of the packing of (I) in the unit cell, viewed down the approximate a-cell direction, showing the zigzag chain-polymer extensions.

3-carboxyanilinium 3-carboxy-4-hydroxybenzenesulfonate

Crystal data

C7H8NO2^+·C7H5O6S^−	F(000) = 736
Mr = 355.31	Dx = 1.620 Mg m^−3
Monoclinic, P21/n	Melting point: 541 K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71069 Å
a = 7.3325 (14) Å	Cell parameters from 25 reflections
b = 31.430 (5) Å	θ = 10.3–17.5°
c = 6.3749 (18) Å	µ = 0.27 mm^−1
β = 97.35 (2)°	T = 297 K
V = 1457.1 (6) Å^3	Prism, pale brown
Z = 4	0.25 × 0.10 × 0.07 mm

Data collection

Rigaku AFC-7R diffractometer	1655 reflections with I > 2σ(I)
Radiation source: Rigaku rotating anode	Rint = 0.040
Graphite monochromator	θmax = 25.0°, θmin = 2.6°
ω–2θ scans	h = −8→4
Absorption correction: ψ scan (TEXSAN for Windows; Molecular Structure Corporation, 1999)	k = 0→37
Tmin = 0.936, Tmax = 0.981	l = −7→7
3013 measured reflections	3 standard reflections every 150 min
2573 independent reflections	intensity decay: 15.8%

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)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.158	H atoms treated by a mixture of independent and constrained refinement
S = 0.90	w = 1/[σ^2(Fo^2) + (0.1P)^2 + 5.4071P] where P = (Fo^2 + 2Fc^2)/3
2573 reflections	(Δ/σ)max = 0.008
241 parameters	Δρmax = 0.28 e Å^−3
0 restraints	Δρmin = −0.37 e Å^−3

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All e.s.d.'s are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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.

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

	x	y	z	Uiso*/Ueq
S5	0.69845 (13)	0.20812 (3)	0.17349 (14)	0.0243 (3)
O2	0.8977 (5)	0.04304 (10)	0.5757 (5)	0.0501 (13)
O51	0.6699 (4)	0.23702 (8)	0.3422 (4)	0.0399 (10)
O52	0.5377 (4)	0.20265 (8)	0.0194 (4)	0.0323 (9)
O53	0.8583 (4)	0.21940 (9)	0.0680 (5)	0.0372 (9)
O71	0.7940 (5)	0.00769 (9)	0.2116 (5)	0.0527 (13)
O72	0.6675 (5)	0.04736 (9)	−0.0567 (5)	0.0458 (10)
C1	0.7702 (5)	0.08173 (11)	0.2643 (6)	0.0287 (11)
C2	0.8466 (5)	0.07979 (12)	0.4770 (6)	0.0320 (12)
C3	0.8720 (6)	0.11682 (13)	0.5963 (6)	0.0348 (14)
C4	0.8241 (5)	0.15583 (12)	0.5053 (6)	0.0292 (11)
C5	0.7506 (5)	0.15801 (11)	0.2930 (6)	0.0241 (11)
C6	0.7239 (5)	0.12168 (11)	0.1737 (6)	0.0267 (11)
C7	0.7452 (6)	0.04283 (12)	0.1373 (7)	0.0361 (12)
O711	0.3273 (5)	0.02781 (9)	0.2533 (5)	0.0525 (13)
O721	0.1735 (5)	0.06575 (9)	−0.0062 (5)	0.0512 (10)
N31	0.2327 (5)	0.21833 (10)	0.2410 (6)	0.0268 (10)
C11	0.2776 (5)	0.10096 (11)	0.3127 (6)	0.0284 (11)
C21	0.2343 (5)	0.14040 (12)	0.2193 (6)	0.0271 (11)
C31	0.2640 (5)	0.17654 (11)	0.3436 (6)	0.0235 (11)
C41	0.3310 (6)	0.17449 (12)	0.5537 (6)	0.0323 (11)
C51	0.3682 (6)	0.13476 (13)	0.6448 (6)	0.0342 (12)
C61	0.3457 (6)	0.09846 (12)	0.5248 (6)	0.0339 (12)
C71	0.2608 (6)	0.06135 (12)	0.1841 (7)	0.0351 (14)
H3	0.924200	0.115200	0.742400	0.0390*
H4	0.841800	0.181500	0.588100	0.0340*
H6	0.672800	0.123700	0.027400	0.0300*
H2	0.858 (7)	0.0223 (16)	0.479 (9)	0.066 (17)*
H72	0.669 (6)	0.0222 (15)	−0.123 (7)	0.052 (14)*
H31A	0.118 (6)	0.2217 (13)	0.184 (7)	0.031 (11)*
H21	0.185800	0.142700	0.073000	0.0310*
H31B	0.299 (7)	0.2198 (15)	0.122 (8)	0.058 (15)*
H31C	0.266 (7)	0.2375 (16)	0.341 (9)	0.064 (17)*
H41	0.352400	0.200000	0.637000	0.0370*
H51	0.410200	0.132500	0.793700	0.0390*
H61	0.377600	0.071300	0.587600	0.0400*
H721	0.184 (6)	0.0411 (15)	−0.075 (7)	0.062 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S5	0.0267 (5)	0.0186 (4)	0.0274 (5)	0.0003 (4)	0.0027 (4)	0.0015 (4)
O2	0.080 (3)	0.0280 (16)	0.0382 (18)	0.0132 (16)	−0.0078 (17)	0.0078 (14)
O51	0.0579 (19)	0.0252 (14)	0.0362 (16)	0.0050 (13)	0.0040 (14)	−0.0065 (12)
O52	0.0322 (15)	0.0314 (15)	0.0313 (15)	0.0018 (12)	−0.0035 (12)	0.0030 (12)
O53	0.0297 (15)	0.0363 (16)	0.0469 (17)	−0.0006 (12)	0.0094 (13)	0.0153 (13)
O71	0.087 (3)	0.0251 (16)	0.0433 (19)	0.0148 (16)	−0.0022 (17)	−0.0008 (14)
O72	0.075 (2)	0.0250 (14)	0.0343 (16)	0.0088 (14)	−0.0055 (15)	−0.0037 (12)
C1	0.030 (2)	0.0235 (19)	0.032 (2)	0.0012 (15)	0.0014 (17)	0.0012 (16)
C2	0.033 (2)	0.028 (2)	0.034 (2)	0.0077 (16)	0.0008 (18)	0.0053 (17)
C3	0.045 (3)	0.034 (2)	0.024 (2)	0.0039 (18)	−0.0005 (18)	0.0023 (16)
C4	0.035 (2)	0.0265 (19)	0.0254 (19)	0.0006 (16)	0.0009 (16)	0.0008 (15)
C5	0.0227 (18)	0.0214 (18)	0.0292 (19)	0.0032 (14)	0.0075 (15)	0.0034 (15)
C6	0.028 (2)	0.0254 (19)	0.0260 (19)	0.0005 (15)	0.0003 (16)	0.0010 (16)
C7	0.041 (2)	0.026 (2)	0.040 (2)	0.0053 (17)	−0.0001 (19)	0.0007 (18)
O711	0.090 (3)	0.0210 (15)	0.0434 (18)	0.0048 (16)	−0.0033 (17)	−0.0039 (13)
O721	0.082 (2)	0.0293 (16)	0.0381 (18)	0.0092 (15)	−0.0087 (17)	−0.0067 (13)
N31	0.0300 (19)	0.0218 (17)	0.0284 (18)	0.0012 (14)	0.0031 (16)	0.0005 (14)
C11	0.029 (2)	0.0234 (19)	0.032 (2)	−0.0026 (15)	0.0006 (17)	−0.0001 (16)
C21	0.028 (2)	0.0282 (19)	0.0252 (19)	−0.0010 (15)	0.0040 (16)	−0.0017 (15)
C31	0.0200 (19)	0.0218 (18)	0.0291 (19)	−0.0004 (14)	0.0051 (15)	0.0035 (15)
C41	0.034 (2)	0.0255 (19)	0.036 (2)	−0.0002 (16)	−0.0007 (18)	−0.0047 (17)
C51	0.038 (2)	0.035 (2)	0.027 (2)	0.0010 (18)	−0.0059 (18)	0.0019 (17)
C61	0.042 (2)	0.025 (2)	0.034 (2)	0.0023 (17)	0.0020 (19)	0.0045 (17)
C71	0.046 (3)	0.024 (2)	0.036 (2)	−0.0031 (17)	0.008 (2)	−0.0039 (17)

Geometric parameters (Å, º)

S5—O51	1.443 (3)	C2—C3	1.390 (6)
S5—O52	1.445 (3)	C3—C4	1.382 (6)
S5—O53	1.467 (3)	C4—C5	1.393 (5)
S5—C5	1.770 (4)	C5—C6	1.372 (5)
O2—C2	1.345 (5)	C3—H3	0.9619
O71—C7	1.236 (5)	C4—H4	0.9638
O72—C7	1.302 (5)	C6—H6	0.9617
O2—H2	0.92 (6)	C11—C21	1.394 (5)
O72—H72	0.90 (5)	C11—C61	1.382 (5)
O711—C71	1.220 (5)	C11—C71	1.487 (5)
O721—C71	1.305 (5)	C21—C31	1.386 (5)
O721—H721	0.90 (5)	C31—C41	1.368 (5)
N31—C31	1.472 (5)	C41—C51	1.389 (6)
N31—H31C	0.89 (6)	C51—C61	1.372 (6)
N31—H31B	0.95 (5)	C21—H21	0.9574
N31—H31A	0.88 (4)	C41—H41	0.9634
C1—C7	1.465 (5)	C51—H51	0.9623
C1—C2	1.401 (5)	C61—H61	0.9590
C1—C6	1.405 (5)
O51—S5—O52	113.45 (17)	O71—C7—O72	122.1 (4)
O51—S5—O53	112.95 (17)	C2—C3—H3	119.63
O51—S5—C5	106.45 (17)	C4—C3—H3	120.10
O52—S5—O53	110.31 (17)	C3—C4—H4	120.23
O52—S5—C5	107.42 (17)	C5—C4—H4	119.95
O53—S5—C5	105.72 (17)	C1—C6—H6	120.08
C2—O2—H2	105 (3)	C5—C6—H6	119.53
C7—O72—H72	109 (3)	C21—C11—C61	120.2 (3)
C71—O721—H721	108 (3)	C21—C11—C71	120.7 (3)
H31A—N31—H31C	112 (4)	C61—C11—C71	119.1 (3)
H31B—N31—H31C	115 (5)	C11—C21—C31	118.3 (3)
H31A—N31—H31B	103 (4)	N31—C31—C41	119.5 (3)
C31—N31—H31A	112 (3)	N31—C31—C21	118.2 (3)
C31—N31—H31B	109 (3)	C21—C31—C41	122.1 (3)
C31—N31—H31C	106 (4)	C31—C41—C51	118.6 (3)
C6—C1—C7	120.8 (3)	C41—C51—C61	120.7 (4)
C2—C1—C7	120.3 (3)	C11—C61—C51	120.1 (4)
C2—C1—C6	118.8 (3)	O711—C71—O721	123.6 (4)
O2—C2—C3	117.0 (3)	O711—C71—C11	121.5 (4)
O2—C2—C1	122.9 (3)	O721—C71—C11	114.8 (3)
C1—C2—C3	120.2 (3)	C11—C21—H21	121.27
C2—C3—C4	120.3 (4)	C31—C21—H21	120.44
C3—C4—C5	119.8 (3)	C31—C41—H41	120.88
C4—C5—C6	120.5 (3)	C51—C41—H41	120.54
S5—C5—C6	119.6 (3)	C41—C51—H51	119.97
S5—C5—C4	119.8 (3)	C61—C51—H51	119.28
C1—C6—C5	120.4 (3)	C11—C61—H61	119.81
O72—C7—C1	116.3 (3)	C51—C61—H61	120.13
O71—C7—C1	121.6 (4)
O51—S5—C5—C4	−24.2 (4)	C3—C4—C5—S5	−177.3 (3)
O51—S5—C5—C6	158.0 (3)	C3—C4—C5—C6	0.5 (6)
O52—S5—C5—C4	−146.0 (3)	S5—C5—C6—C1	177.9 (3)
O52—S5—C5—C6	36.1 (4)	C4—C5—C6—C1	0.1 (6)
O53—S5—C5—C4	96.2 (3)	C61—C11—C21—C31	1.0 (6)
O53—S5—C5—C6	−81.7 (3)	C71—C11—C21—C31	−175.8 (4)
C6—C1—C7—O72	−4.4 (6)	C21—C11—C61—C51	1.0 (6)
C7—C1—C2—O2	−1.0 (6)	C71—C11—C61—C51	177.8 (4)
C6—C1—C7—O71	176.2 (4)	C21—C11—C71—O711	167.1 (4)
C6—C1—C2—O2	−178.9 (4)	C21—C11—C71—O721	−11.8 (6)
C6—C1—C2—C3	1.4 (6)	C61—C11—C71—O721	171.4 (4)
C2—C1—C6—C5	−1.0 (6)	C61—C11—C71—O711	−9.7 (6)
C7—C1—C6—C5	−178.9 (4)	C11—C21—C31—C41	−1.1 (6)
C7—C1—C2—C3	179.3 (4)	C11—C21—C31—N31	175.1 (3)
C2—C1—C7—O71	−1.7 (6)	N31—C31—C41—C51	−176.8 (4)
C2—C1—C7—O72	177.7 (4)	C21—C31—C41—C51	−0.7 (6)
C1—C2—C3—C4	−0.8 (6)	C31—C41—C51—C61	2.7 (7)
O2—C2—C3—C4	179.5 (4)	C41—C51—C61—C11	−2.9 (7)
C2—C3—C4—C5	−0.2 (6)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O71	0.92 (6)	1.77 (6)	2.598 (5)	149 (5)
O72—H72···O711^i	0.90 (5)	1.78 (5)	2.677 (4)	180 (6)
O721—H721···O71^i	0.90 (5)	1.78 (5)	2.679 (4)	180 (6)
N31—H31A···O53^ii	0.88 (4)	1.95 (4)	2.825 (5)	171 (4)
N31—H31B···O52	0.95 (5)	2.02 (5)	2.837 (5)	143 (4)
N31—H31B···O51^iii	0.95 (5)	2.34 (5)	2.889 (5)	116 (4)
N31—H31C···O53^iv	0.89 (6)	2.03 (6)	2.921 (5)	177 (5)
C4—H4···O51	0.96	2.57	2.928 (5)	102
C41—H41···O53^iv	0.96	2.57	3.342 (5)	137

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