organic compounds
4-Chloroanilinium 2-carboxy-4,5-dichlorobenzoate
aSchool of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia, and bBIO-21 Molecular Science and Biotechnology, University of Melbourne, Parkville, Victoria 3052, Australia
*Correspondence e-mail: g.smith@qut.edu.au
The structure of the 1:1 proton-transfer compound of 4-chloroaniline with 4,5-dichlorophthalic acid (DCPA), viz. C6H7ClN+·C8H3Cl2O4−, has been determined at 130 K. The non-planar hydrogen phthalate anions and the 4-chloroanilinium cations form two-dimensional O—H⋯O and N—H⋯O hydrogen-bonded substructures which have no peripheral extension. Between the sheets there are weak π–π associations between alternating cation–anion aromatic ring systems [shortest centroid–centroid separation = 3.735 (4) Å].
Related literature
For the structures of other hydrogen DCPA salts with aromatic Lewis bases showing similar two-dimensional substructures, see: Smith et al. (2008b). This contrasts with the majority of the compounds in which the DCPA anion is planar with a short intramolecular carboxylic acid hydrogen bond, see: Smith et al. (2007, 2008a, 2009).
Experimental
Crystal data
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Data collection: CrysAlis CCD (Oxford Diffraction, 2007); cell CrysAlis RED (Oxford Diffraction, 2007); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: PLATON.
Supporting information
10.1107/S160053680903044X/at2844sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S160053680903044X/at2844Isup2.hkl
The title compound (I) was synthesized by heating together 1 mmol quantities of 4-chloroaniline and 4,5-dichlorophthalic acid in 50 ml of 50% aqueous methanol for 10 min under reflux. After concentration to ca. 30 ml, partial room-temperature evaporation of the hot-filtered solution gave small colourless plates [m.p. 492 K]).
Hydrogen 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
at calculated positions [C–H, 0.93 Å] and treated as riding models with Uiso(H) = 1.2Ueq (C).Data collection: CrysAlis CCD (Oxford Diffraction, 2007); cell
CrysAlis RED (Oxford Diffraction, 2007); data reduction: CrysAlis RED (Oxford Diffraction, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: PLATON (Spek, 2009).Fig. 1. Molecular configuration and atom numbering scheme for the 4-chloroanilinium cation and the hydrogen 4,5-dichlorophthalate anion in (I). Non-H atoms are shown as 50% probability displacement ellipsoids. Hydrogen bonds are shown as dashed lines. | |
Fig. 2. The two-dimensional sheet structure in (I) viewed down the b axis in the unit cell. Non-interactive H atoms are omitted and hydrogen bonds are shown as dashed lines. (For symmetry codes, see Table 1). |
C6H7ClN+·C8H3Cl2O4− | F(000) = 736 |
Mr = 362.58 | Dx = 1.634 Mg m−3 |
Monoclinic, C2 | Melting point: 492 K |
Hall symbol: C 2y | Cu Kα radiation, λ = 1.54184 Å |
a = 12.8171 (8) Å | Cell parameters from 1721 reflections |
b = 7.5954 (3) Å | θ = 2.9–71.8° |
c = 16.0909 (6) Å | µ = 5.80 mm−1 |
β = 109.815 (5)° | T = 130 K |
V = 1473.72 (13) Å3 | Plate, colourless |
Z = 4 | 0.34 × 0.27 × 0.05 mm |
Oxford Diffraction Gemini Ultra CCD-detector diffractometer | 2288 independent reflections |
Radiation source: Enhance Ultra (Cu) X-ray source | 1879 reflections with I > 2σ(I) |
Mirror monochromator | Rint = 0.061 |
ω scans | θmax = 72.1°, θmin = 2.9° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −15→14 |
Tmin = 0.201, Tmax = 0.748 | k = −9→8 |
3680 measured reflections | l = −15→19 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.062 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.175 | w = 1/[σ2(Fo2) + (0.135P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.00 | (Δ/σ)max < 0.001 |
2288 reflections | Δρmax = 0.64 e Å−3 |
215 parameters | Δρmin = −0.56 e Å−3 |
1 restraint | Absolute structure: Flack (1983), 723 Friedel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.04 (3) |
C6H7ClN+·C8H3Cl2O4− | V = 1473.72 (13) Å3 |
Mr = 362.58 | Z = 4 |
Monoclinic, C2 | Cu Kα radiation |
a = 12.8171 (8) Å | µ = 5.80 mm−1 |
b = 7.5954 (3) Å | T = 130 K |
c = 16.0909 (6) Å | 0.34 × 0.27 × 0.05 mm |
β = 109.815 (5)° |
Oxford Diffraction Gemini Ultra CCD-detector diffractometer | 2288 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 1879 reflections with I > 2σ(I) |
Tmin = 0.201, Tmax = 0.748 | Rint = 0.061 |
3680 measured reflections |
R[F2 > 2σ(F2)] = 0.062 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.175 | Δρmax = 0.64 e Å−3 |
S = 1.00 | Δρmin = −0.56 e Å−3 |
2288 reflections | Absolute structure: Flack (1983), 723 Friedel pairs |
215 parameters | Absolute structure parameter: 0.04 (3) |
1 restraint |
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su'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. |
x | y | z | Uiso*/Ueq | ||
Cl4 | 0.39571 (14) | 0.8094 (3) | 0.55613 (9) | 0.0377 (5) | |
Cl5 | 0.37318 (14) | 0.3980 (3) | 0.58289 (9) | 0.0418 (5) | |
O11 | 0.5642 (4) | 0.3295 (7) | 0.9286 (3) | 0.0348 (14) | |
O12 | 0.6750 (3) | 0.5632 (6) | 0.9688 (2) | 0.0282 (11) | |
O21 | 0.7198 (3) | 0.9010 (6) | 0.8943 (2) | 0.0243 (10) | |
O22 | 0.5704 (3) | 0.9285 (6) | 0.9364 (2) | 0.0272 (13) | |
C1 | 0.5441 (5) | 0.5652 (8) | 0.8257 (4) | 0.0244 (16) | |
C2 | 0.5583 (5) | 0.7457 (8) | 0.8141 (3) | 0.0222 (16) | |
C3 | 0.5118 (5) | 0.8181 (9) | 0.7299 (4) | 0.0257 (16) | |
C4 | 0.4522 (5) | 0.7126 (9) | 0.6581 (4) | 0.0289 (18) | |
C5 | 0.4402 (5) | 0.5333 (9) | 0.6707 (4) | 0.0311 (18) | |
C6 | 0.4861 (5) | 0.4599 (9) | 0.7537 (4) | 0.0276 (17) | |
C11 | 0.5956 (5) | 0.4739 (9) | 0.9139 (4) | 0.0244 (17) | |
C21 | 0.6212 (4) | 0.8673 (7) | 0.8897 (3) | 0.0237 (16) | |
Cl4A | 0.13666 (14) | 0.6564 (2) | 0.60330 (9) | 0.0387 (5) | |
N1A | 0.3688 (4) | 1.1240 (7) | 0.9059 (3) | 0.0234 (14) | |
C1A | 0.3149 (5) | 1.0096 (8) | 0.8304 (3) | 0.0233 (16) | |
C2A | 0.2717 (5) | 1.0813 (9) | 0.7460 (4) | 0.0292 (17) | |
C3A | 0.2162 (5) | 0.9729 (9) | 0.6753 (4) | 0.0300 (18) | |
C4A | 0.2064 (5) | 0.7965 (9) | 0.6903 (4) | 0.0286 (17) | |
C5A | 0.2510 (5) | 0.7210 (9) | 0.7743 (4) | 0.0283 (17) | |
C6A | 0.3054 (5) | 0.8316 (9) | 0.8443 (3) | 0.0263 (18) | |
H3 | 0.52050 | 0.93760 | 0.72140 | 0.0310* | |
H6 | 0.47830 | 0.34000 | 0.76170 | 0.0340* | |
H12 | 0.700 (3) | 0.509 (4) | 1.015 (2) | 0.042 (11)* | |
H2A | 0.27990 | 1.20080 | 0.73710 | 0.0340* | |
H3A | 0.18610 | 1.01900 | 0.61860 | 0.0360* | |
H5A | 0.24450 | 0.60100 | 0.78290 | 0.0340* | |
H6A | 0.33560 | 0.78560 | 0.90100 | 0.0320* | |
H11A | 0.425 (3) | 1.179 (4) | 0.897 (3) | 0.035 (10)* | |
H12A | 0.393 (4) | 1.059 (3) | 0.954 (2) | 0.041 (11)* | |
H13A | 0.320 (4) | 1.202 (4) | 0.910 (3) | 0.038 (11)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Cl4 | 0.0444 (9) | 0.0546 (10) | 0.0141 (6) | −0.0005 (8) | 0.0035 (5) | 0.0056 (6) |
Cl5 | 0.0482 (10) | 0.0479 (10) | 0.0206 (6) | −0.0014 (8) | 0.0002 (6) | −0.0120 (6) |
O11 | 0.038 (2) | 0.035 (3) | 0.026 (2) | −0.011 (2) | 0.0037 (17) | 0.0002 (19) |
O12 | 0.031 (2) | 0.034 (2) | 0.0147 (17) | 0.0000 (18) | 0.0015 (15) | 0.0039 (16) |
O21 | 0.0266 (18) | 0.031 (2) | 0.0155 (15) | −0.0022 (18) | 0.0075 (14) | −0.0015 (15) |
O22 | 0.026 (2) | 0.033 (3) | 0.0203 (17) | 0.0019 (17) | 0.0050 (15) | −0.0038 (16) |
C1 | 0.028 (3) | 0.027 (3) | 0.017 (2) | 0.001 (2) | 0.006 (2) | −0.004 (2) |
C2 | 0.023 (3) | 0.029 (3) | 0.015 (2) | −0.001 (2) | 0.007 (2) | −0.001 (2) |
C3 | 0.028 (3) | 0.029 (3) | 0.020 (2) | 0.001 (3) | 0.008 (2) | −0.001 (2) |
C4 | 0.029 (3) | 0.043 (4) | 0.011 (2) | 0.002 (3) | 0.002 (2) | 0.000 (2) |
C5 | 0.030 (3) | 0.041 (4) | 0.017 (2) | −0.005 (3) | 0.001 (2) | −0.006 (3) |
C6 | 0.030 (3) | 0.031 (3) | 0.024 (3) | −0.003 (3) | 0.012 (2) | −0.002 (2) |
C11 | 0.022 (3) | 0.033 (3) | 0.019 (3) | −0.003 (2) | 0.008 (2) | −0.001 (2) |
C21 | 0.023 (3) | 0.030 (3) | 0.018 (2) | −0.002 (2) | 0.007 (2) | −0.001 (2) |
Cl4A | 0.0489 (9) | 0.0436 (10) | 0.0201 (6) | −0.0072 (8) | 0.0073 (6) | −0.0054 (6) |
N1A | 0.023 (2) | 0.030 (3) | 0.016 (2) | 0.001 (2) | 0.0050 (16) | 0.0040 (19) |
C1A | 0.024 (3) | 0.029 (3) | 0.017 (2) | −0.004 (2) | 0.007 (2) | −0.003 (2) |
C2A | 0.036 (3) | 0.029 (3) | 0.020 (3) | 0.005 (3) | 0.006 (2) | 0.001 (2) |
C3A | 0.034 (3) | 0.039 (4) | 0.016 (2) | 0.000 (3) | 0.007 (2) | 0.001 (2) |
C4A | 0.035 (3) | 0.029 (3) | 0.022 (3) | 0.003 (3) | 0.010 (2) | 0.000 (2) |
C5A | 0.032 (3) | 0.031 (3) | 0.021 (3) | −0.002 (3) | 0.008 (2) | 0.002 (2) |
C6A | 0.029 (3) | 0.032 (4) | 0.018 (2) | 0.000 (3) | 0.008 (2) | 0.002 (2) |
Cl4—C4 | 1.718 (6) | C2—C3 | 1.395 (8) |
Cl5—C5 | 1.723 (7) | C3—C4 | 1.401 (9) |
Cl4A—C4A | 1.744 (7) | C4—C5 | 1.393 (10) |
O11—C11 | 1.219 (9) | C5—C6 | 1.381 (9) |
O12—C11 | 1.291 (8) | C3—H3 | 0.9300 |
O21—C21 | 1.267 (7) | C6—H6 | 0.9300 |
O22—C21 | 1.240 (6) | C1A—C6A | 1.383 (9) |
O12—H12 | 0.81 (3) | C1A—C2A | 1.392 (8) |
N1A—C1A | 1.463 (7) | C2A—C3A | 1.389 (9) |
N1A—H13A | 0.89 (4) | C3A—C4A | 1.375 (10) |
N1A—H12A | 0.88 (3) | C4A—C5A | 1.400 (9) |
N1A—H11A | 0.88 (4) | C5A—C6A | 1.389 (8) |
C1—C2 | 1.404 (9) | C2A—H2A | 0.9300 |
C1—C11 | 1.515 (9) | C3A—H3A | 0.9300 |
C1—C6 | 1.397 (9) | C5A—H5A | 0.9300 |
C2—C21 | 1.523 (7) | C6A—H6A | 0.9300 |
C11—O12—H12 | 110 (2) | O22—C21—C2 | 117.9 (5) |
H11A—N1A—H12A | 110 (4) | O21—C21—C2 | 114.6 (5) |
H11A—N1A—H13A | 109 (4) | C2—C3—H3 | 120.00 |
C1A—N1A—H13A | 108 (3) | C4—C3—H3 | 120.00 |
C1A—N1A—H11A | 109 (3) | C5—C6—H6 | 120.00 |
H12A—N1A—H13A | 111 (4) | C1—C6—H6 | 120.00 |
C6—C1—C11 | 117.1 (6) | C2A—C1A—C6A | 120.9 (5) |
C2—C1—C11 | 122.5 (5) | N1A—C1A—C6A | 119.3 (4) |
C2—C1—C6 | 120.4 (5) | N1A—C1A—C2A | 119.8 (5) |
C1—C2—C3 | 118.8 (5) | C1A—C2A—C3A | 119.4 (6) |
C3—C2—C21 | 118.2 (5) | C2A—C3A—C4A | 119.1 (6) |
C1—C2—C21 | 122.9 (5) | Cl4A—C4A—C3A | 120.4 (5) |
C2—C3—C4 | 120.6 (6) | Cl4A—C4A—C5A | 117.1 (5) |
C3—C4—C5 | 119.7 (6) | C3A—C4A—C5A | 122.5 (6) |
Cl4—C4—C5 | 121.7 (5) | C4A—C5A—C6A | 117.6 (6) |
Cl4—C4—C3 | 118.6 (5) | C1A—C6A—C5A | 120.5 (5) |
Cl5—C5—C6 | 118.9 (5) | C1A—C2A—H2A | 120.00 |
C4—C5—C6 | 120.2 (6) | C3A—C2A—H2A | 120.00 |
Cl5—C5—C4 | 120.9 (5) | C2A—C3A—H3A | 120.00 |
C1—C6—C5 | 120.2 (6) | C4A—C3A—H3A | 120.00 |
O11—C11—C1 | 121.7 (6) | C4A—C5A—H5A | 121.00 |
O11—C11—O12 | 125.1 (6) | C6A—C5A—H5A | 121.00 |
O12—C11—C1 | 113.1 (6) | C1A—C6A—H6A | 120.00 |
O21—C21—O22 | 127.4 (5) | C5A—C6A—H6A | 120.00 |
C6—C1—C2—C3 | 1.2 (10) | C2—C3—C4—C5 | −0.7 (10) |
C6—C1—C2—C21 | −179.6 (6) | Cl4—C4—C5—Cl5 | 3.1 (9) |
C11—C1—C2—C3 | 177.4 (6) | Cl4—C4—C5—C6 | −179.6 (5) |
C11—C1—C2—C21 | −3.4 (10) | C3—C4—C5—Cl5 | −176.9 (5) |
C2—C1—C6—C5 | −1.4 (10) | C3—C4—C5—C6 | 0.5 (10) |
C11—C1—C6—C5 | −177.8 (6) | Cl5—C5—C6—C1 | 177.9 (5) |
C2—C1—C11—O11 | 163.7 (7) | C4—C5—C6—C1 | 0.5 (10) |
C2—C1—C11—O12 | −17.4 (9) | N1A—C1A—C2A—C3A | −177.1 (6) |
C6—C1—C11—O11 | −20.0 (10) | C6A—C1A—C2A—C3A | 1.5 (10) |
C6—C1—C11—O12 | 159.0 (6) | N1A—C1A—C6A—C5A | 177.6 (6) |
C1—C2—C3—C4 | −0.2 (10) | C2A—C1A—C6A—C5A | −0.9 (10) |
C21—C2—C3—C4 | −179.4 (6) | C1A—C2A—C3A—C4A | −0.8 (10) |
C1—C2—C21—O21 | 100.2 (7) | C2A—C3A—C4A—Cl4A | 179.7 (5) |
C1—C2—C21—O22 | −83.3 (8) | C2A—C3A—C4A—C5A | −0.5 (10) |
C3—C2—C21—O21 | −80.6 (7) | Cl4A—C4A—C5A—C6A | −179.1 (5) |
C3—C2—C21—O22 | 95.9 (7) | C3A—C4A—C5A—C6A | 1.0 (10) |
C2—C3—C4—Cl4 | 179.4 (5) | C4A—C5A—C6A—C1A | −0.3 (10) |
D—H···A | D—H | H···A | D···A | D—H···A |
O12—H12···O21i | 0.81 (3) | 1.69 (3) | 2.485 (5) | 166 (4) |
N1A—H11A···O11ii | 0.89 (4) | 2.03 (4) | 2.867 (8) | 157 (4) |
N1A—H11A···O22 | 0.89 (4) | 2.59 (4) | 2.875 (7) | 100 (2) |
N1A—H12A···O22 | 0.88 (3) | 2.58 (5) | 2.875 (7) | 100 (3) |
N1A—H12A···O22iii | 0.88 (3) | 1.94 (3) | 2.813 (6) | 172 (5) |
N1A—H13A···O12iv | 0.88 (4) | 2.58 (5) | 3.019 (7) | 112 (3) |
N1A—H13A···O21iv | 0.88 (4) | 1.94 (4) | 2.805 (7) | 166 (4) |
C5A—H5A···O21v | 0.93 | 2.45 | 3.212 (8) | 139 |
Symmetry codes: (i) −x+3/2, y−1/2, −z+2; (ii) x, y+1, z; (iii) −x+1, y, −z+2; (iv) x−1/2, y+1/2, z; (v) x−1/2, y−1/2, z. |
Experimental details
Crystal data | |
Chemical formula | C6H7ClN+·C8H3Cl2O4− |
Mr | 362.58 |
Crystal system, space group | Monoclinic, C2 |
Temperature (K) | 130 |
a, b, c (Å) | 12.8171 (8), 7.5954 (3), 16.0909 (6) |
β (°) | 109.815 (5) |
V (Å3) | 1473.72 (13) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 5.80 |
Crystal size (mm) | 0.34 × 0.27 × 0.05 |
Data collection | |
Diffractometer | Oxford Diffraction Gemini Ultra CCD-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.201, 0.748 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3680, 2288, 1879 |
Rint | 0.061 |
(sin θ/λ)max (Å−1) | 0.617 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.062, 0.175, 1.00 |
No. of reflections | 2288 |
No. of parameters | 215 |
No. of restraints | 1 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.64, −0.56 |
Absolute structure | Flack (1983), 723 Friedel pairs |
Absolute structure parameter | 0.04 (3) |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2007), CrysAlis RED (Oxford Diffraction, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009).
D—H···A | D—H | H···A | D···A | D—H···A |
O12—H12···O21i | 0.81 (3) | 1.69 (3) | 2.485 (5) | 166 (4) |
N1A—H11A···O11ii | 0.89 (4) | 2.03 (4) | 2.867 (8) | 157 (4) |
N1A—H11A···O22 | 0.89 (4) | 2.59 (4) | 2.875 (7) | 100 (2) |
N1A—H12A···O22 | 0.88 (3) | 2.58 (5) | 2.875 (7) | 100 (3) |
N1A—H12A···O22iii | 0.88 (3) | 1.94 (3) | 2.813 (6) | 172 (5) |
N1A—H13A···O12iv | 0.88 (4) | 2.58 (5) | 3.019 (7) | 112 (3) |
N1A—H13A···O21iv | 0.88 (4) | 1.94 (4) | 2.805 (7) | 166 (4) |
Symmetry codes: (i) −x+3/2, y−1/2, −z+2; (ii) x, y+1, z; (iii) −x+1, y, −z+2; (iv) x−1/2, y+1/2, z. |
Acknowledgements
The authors acknowledge financial support from the School of Physical and Chemical Sciences (Queensland University of Technology) and the School of Chemistry, the University of Melbourne.
References
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Among the known structures of the 1:1 aromatic Lewis base compounds of 4,5-dichlorophthalic acid (DCPA), a small number have similar hydrogen-bonded substructures in which the basic N+—H···Ocarboxyl linked cation–anion unit is propagated in two dimensions (Smith et al., 2008b). In these the DCPA anions are non-planar with the carboxylic acid and carboxylate groups rotated out of the plane of the benzene ring. This contrasts with the majority of the compounds in which the DCPA anion is planar with a short intramolecular carboxylic acid O–H···Ocarboxyl hydrogen bond (Smith et al., 2007, 2008a, 2009). Since the examples having the two-dimensional substructures were substituted anilines, the 4-chloro-analogue was reacted with DCPA, giving anhydrous 4-chloroanilinium 2-carboxy-4,5-dichlorobenzoate C6H7ClN+. C8H3Cl2O4- (I) and its structure is reported here.
In (I), as expected, the primary hydrogen-bonded cation–anion structural unit (Fig.1) provides the basis for formation of the previously described two-dimensional substructure which extends across the ab plane in the unit cell, having no lateral interactions (Fig. 2). The hydrogen bonding within the plane (Table 1) includes a cyclic R21(6) anilinium–H···O12,O21 interaction. The alternating cation–anion aromatic ring systems (C1–C6 and C1A–C6A) give weak π–π interactions [shortest centroid separation 3.735 (4) Å]. The hydrogen 4,5-dichlorophthalate anion is non-planar [torsion angles C2–C1–C11–O11, 163.7 (7)°: C1–C2–C21–O22, -83.3 (8)°].,