organic compounds
4-Aminopyridinium cis-2-carboxycyclohexane-1-carboxylate
aFaculty of Science and Technology, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia
*Correspondence e-mail: g.smith@qut.edu.au
In the structure of the title molecular salt, C5H7N2+·C8H11O4−, the cis monoanions associate through short O—H⋯O hydrogen bonds in the carboxylic acid groups [graph set C(7)], forming zigzag chains which extend along the c axis. These are interlinked through pyridinium and amine N—H⋯O hydrogen bonds, giving a three-dimensional network structure.
Related literature
For the structure of racemic cis-cyclohexane-1,2-dicarboxylic acid, see: Benedetti et al. (1970). For the structure of the racemic ammonium and 2-aminopyridinium salts of cis-2-carboxycyclohexane-1-carboxylate, see: Smith & Wermuth (2011a,b). For graph-set analysis, see Etter et al. (1990).
Experimental
Crystal data
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Refinement
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Data collection: CrysAlis PRO (Oxford Diffraction, 2010); cell CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) within WinGX (Farrugia, 1999); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: PLATON.
Supporting information
https://doi.org/10.1107/S1600536811039547/fj2453sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536811039547/fj2453Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S1600536811039547/fj2453Isup3.cml
The title compound was synthesized by heating a solution of 1 mmol of cyclohexane-1,2-dicarboxylic anhydride and 1 mmol of 4-aminopyridine in 50 ml of 1:1 ethanol–water under reflux for 10 min. After concentration to 30 ml the solution was allowed to evaporate at room temperature, giving finally a residual viscous oil in which minor well formed colourless crystals of the title compound were found.
Hydrogen atoms 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 = 0.93–0.98 Å] and with Uiso(H) = 1.2Ueq(C), using a riding-model approximation. In the absence of a suitable heavy atom in the structure, the Friedel pairs (1332) were merged for the final cycles of the In the structure reported here, the cis-CHDC anion has the (1S,2R) configuration.The structures of
salts of cis-cyclohexane-1,2-dicarboxylic acid (cis-CHDC) are rare in the crystallographic literature and like the parent cis-acid (Benedetti et al., 1970), exist only in the unresolved racemic form. We have reported the structures of the 1:1 ammonium salt (Smith & Wermuth, 2011a) and the 1:1 2-aminopyridinium salt (Smith & Wermuth, 2011b) and in our parallel 1:1 stoichiometric reaction of cis-CHDC anhydride with 4-aminopyridine in 50% ethanol–water solution we also obtained minor crystals of the title compound, cis-C5H7N2+ C8H11O4- (Fig. 1) and the structure is reported here.In the structure of the title compound, the monoanions associate through strong carboxylic acid–carboxyl O—H···O hydrogen bonds (Table 1) giving zigzag chains [graph set C(7) (Etter et al., 1990)] which extend along c (Fig. 2). The cations provide links between these chains through both pyridinium and amine N—H···Ocarboxyl hydrogen bonds, resulting in a three-dimensional structure (Figs. 2,3).
For the structure of racemic cis-cyclohexane-1,2-dicarboxylic acid, see: Benedetti et al. (1970). For the structure of the racemic ammonium and 2-aminopyridinium salts of cis-2-carboxycyclohexane-1-carboxylate, see: Smith & Wermuth (2011a,b). For graph-set analysis, see Etter et al. (1990).
Data collection: CrysAlis PRO (Oxford Diffraction, 2010); cell
CrysAlis PRO (Oxford Diffraction, 2010); data reduction: CrysAlis PRO (Oxford Diffraction, 2010); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) within WinGX (Farrugia, 1999); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: PLATON (Spek, 2009).C5H7N2+·C8H11O4− | F(000) = 568 |
Mr = 266.29 | Dx = 1.325 Mg m−3 |
Orthorhombic, Pna21 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2c -2n | Cell parameters from 4840 reflections |
a = 12.1359 (3) Å | θ = 3.2–28.7° |
b = 9.8351 (3) Å | µ = 0.10 mm−1 |
c = 11.1850 (3) Å | T = 200 K |
V = 1335.02 (6) Å3 | Block, colourless |
Z = 4 | 0.30 × 0.25 × 0.20 mm |
Oxford Diffraction Gemini-S CCD-detector diffractometer | 1709 independent reflections |
Radiation source: Enhance (Mo) X-ray source | 1448 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.029 |
Detector resolution: 16.077 pixels mm-1 | θmax = 28.8°, θmin = 3.2° |
ω scans | h = −16→15 |
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2010) | k = −12→13 |
Tmin = 0.948, Tmax = 0.990 | l = −13→15 |
9670 measured reflections |
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)] = 0.028 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.060 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.99 | w = 1/[σ2(Fo2) + (0.0357P)2] where P = (Fo2 + 2Fc2)/3 |
1709 reflections | (Δ/σ)max < 0.001 |
188 parameters | Δρmax = 0.15 e Å−3 |
1 restraint | Δρmin = −0.16 e Å−3 |
C5H7N2+·C8H11O4− | V = 1335.02 (6) Å3 |
Mr = 266.29 | Z = 4 |
Orthorhombic, Pna21 | Mo Kα radiation |
a = 12.1359 (3) Å | µ = 0.10 mm−1 |
b = 9.8351 (3) Å | T = 200 K |
c = 11.1850 (3) Å | 0.30 × 0.25 × 0.20 mm |
Oxford Diffraction Gemini-S CCD-detector diffractometer | 1709 independent reflections |
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2010) | 1448 reflections with I > 2σ(I) |
Tmin = 0.948, Tmax = 0.990 | Rint = 0.029 |
9670 measured reflections |
R[F2 > 2σ(F2)] = 0.028 | 1 restraint |
wR(F2) = 0.060 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.99 | Δρmax = 0.15 e Å−3 |
1709 reflections | Δρmin = −0.16 e Å−3 |
188 parameters |
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 | ||
O11 | −0.08623 (9) | 0.42384 (12) | 0.16082 (11) | 0.0293 (4) | |
O12 | 0.08627 (8) | 0.38250 (12) | 0.21757 (10) | 0.0262 (3) | |
O21 | 0.01171 (10) | 0.40723 (12) | 0.51058 (12) | 0.0285 (3) | |
O22 | 0.17703 (9) | 0.30714 (12) | 0.50187 (12) | 0.0296 (3) | |
C1 | −0.06239 (12) | 0.25883 (16) | 0.31330 (14) | 0.0202 (4) | |
C2 | 0.02258 (13) | 0.20096 (16) | 0.40246 (15) | 0.0223 (5) | |
C3 | 0.10393 (14) | 0.10098 (18) | 0.34520 (18) | 0.0311 (5) | |
C4 | 0.04378 (15) | −0.01169 (19) | 0.2767 (2) | 0.0410 (6) | |
C5 | −0.03704 (15) | 0.04676 (19) | 0.18597 (18) | 0.0340 (6) | |
C6 | −0.11879 (14) | 0.14099 (17) | 0.24603 (17) | 0.0272 (5) | |
C11 | −0.01574 (12) | 0.36284 (16) | 0.22481 (14) | 0.0200 (5) | |
C21 | 0.07930 (13) | 0.30994 (17) | 0.47466 (14) | 0.0222 (5) | |
N1A | 0.16603 (12) | 0.28917 (15) | 0.99803 (15) | 0.0301 (4) | |
N41A | 0.30073 (13) | 0.14997 (18) | 0.68510 (15) | 0.0320 (5) | |
C2A | 0.14635 (14) | 0.35553 (19) | 0.89470 (16) | 0.0306 (5) | |
C3A | 0.18908 (13) | 0.31222 (17) | 0.78984 (16) | 0.0285 (5) | |
C4A | 0.25659 (12) | 0.19462 (16) | 0.78670 (15) | 0.0236 (5) | |
C5A | 0.27516 (14) | 0.12848 (18) | 0.89698 (16) | 0.0289 (5) | |
C6A | 0.22940 (14) | 0.17671 (18) | 0.99826 (17) | 0.0309 (5) | |
H1 | −0.11940 | 0.30510 | 0.36020 | 0.0240* | |
H2 | −0.02010 | 0.14740 | 0.46010 | 0.0270* | |
H21 | 0.046 (2) | 0.473 (3) | 0.561 (3) | 0.069 (8)* | |
H31B | 0.15200 | 0.14990 | 0.29080 | 0.0370* | |
H32B | 0.14940 | 0.06050 | 0.40700 | 0.0370* | |
H41B | 0.09730 | −0.06800 | 0.23550 | 0.0490* | |
H42B | 0.00420 | −0.06880 | 0.33280 | 0.0490* | |
H51B | 0.00320 | 0.09640 | 0.12510 | 0.0410* | |
H52B | −0.07640 | −0.02690 | 0.14720 | 0.0410* | |
H61B | −0.16300 | 0.08910 | 0.30200 | 0.0330* | |
H62B | −0.16790 | 0.17830 | 0.18600 | 0.0330* | |
H1A | 0.1408 (18) | 0.319 (2) | 1.0674 (19) | 0.038 (6)* | |
H2A | 0.10230 | 0.43290 | 0.89560 | 0.0370* | |
H3A | 0.17420 | 0.35960 | 0.71970 | 0.0340* | |
H5A | 0.31920 | 0.05120 | 0.89970 | 0.0350* | |
H6A | 0.24190 | 0.13130 | 1.06990 | 0.0370* | |
H41A | 0.3409 (18) | 0.078 (2) | 0.687 (2) | 0.047 (6)* | |
H42A | 0.2841 (16) | 0.193 (2) | 0.615 (2) | 0.038 (6)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O11 | 0.0297 (6) | 0.0270 (6) | 0.0312 (7) | 0.0010 (5) | −0.0051 (5) | 0.0106 (6) |
O12 | 0.0244 (6) | 0.0291 (6) | 0.0251 (6) | −0.0047 (5) | 0.0004 (5) | 0.0028 (5) |
O21 | 0.0321 (6) | 0.0263 (6) | 0.0272 (6) | 0.0042 (5) | −0.0021 (6) | −0.0066 (6) |
O22 | 0.0304 (6) | 0.0316 (6) | 0.0269 (6) | 0.0036 (5) | −0.0062 (5) | −0.0019 (6) |
C1 | 0.0205 (7) | 0.0188 (8) | 0.0212 (8) | 0.0009 (6) | 0.0009 (6) | −0.0003 (7) |
C2 | 0.0267 (8) | 0.0193 (8) | 0.0209 (8) | −0.0009 (7) | 0.0007 (7) | 0.0046 (7) |
C3 | 0.0325 (9) | 0.0253 (9) | 0.0354 (10) | 0.0084 (8) | −0.0064 (8) | −0.0016 (8) |
C4 | 0.0439 (10) | 0.0247 (9) | 0.0543 (13) | 0.0080 (8) | −0.0046 (10) | −0.0118 (9) |
C5 | 0.0387 (10) | 0.0270 (9) | 0.0363 (11) | −0.0064 (8) | −0.0040 (9) | −0.0106 (8) |
C6 | 0.0269 (8) | 0.0226 (8) | 0.0322 (10) | −0.0068 (7) | −0.0053 (7) | 0.0039 (8) |
C11 | 0.0254 (8) | 0.0166 (8) | 0.0179 (8) | −0.0006 (6) | −0.0006 (6) | −0.0031 (6) |
C21 | 0.0287 (8) | 0.0222 (8) | 0.0157 (8) | 0.0017 (7) | −0.0004 (6) | 0.0051 (7) |
N1A | 0.0318 (7) | 0.0344 (8) | 0.0240 (8) | 0.0016 (6) | 0.0021 (7) | −0.0067 (8) |
N41A | 0.0366 (8) | 0.0293 (9) | 0.0302 (9) | 0.0098 (7) | 0.0024 (7) | −0.0044 (7) |
C2A | 0.0324 (9) | 0.0258 (9) | 0.0335 (10) | 0.0077 (8) | 0.0012 (8) | −0.0007 (9) |
C3A | 0.0334 (9) | 0.0241 (9) | 0.0281 (9) | 0.0057 (7) | −0.0019 (8) | 0.0023 (8) |
C4A | 0.0225 (7) | 0.0209 (8) | 0.0275 (9) | −0.0010 (6) | −0.0021 (7) | −0.0032 (8) |
C5A | 0.0305 (9) | 0.0233 (9) | 0.0329 (10) | 0.0054 (7) | −0.0085 (8) | −0.0012 (8) |
C6A | 0.0334 (9) | 0.0328 (9) | 0.0264 (9) | −0.0001 (8) | −0.0080 (8) | 0.0013 (9) |
O11—C11 | 1.2665 (19) | C1—H1 | 0.9800 |
O12—C11 | 1.2556 (18) | C2—H2 | 0.9800 |
O21—C21 | 1.323 (2) | C3—H32B | 0.9700 |
O22—C21 | 1.2248 (19) | C3—H31B | 0.9700 |
O21—H21 | 0.95 (3) | C4—H42B | 0.9700 |
N1A—C6A | 1.347 (2) | C4—H41B | 0.9700 |
N1A—C2A | 1.349 (2) | C5—H51B | 0.9700 |
N41A—C4A | 1.331 (2) | C5—H52B | 0.9700 |
N1A—H1A | 0.88 (2) | C6—H61B | 0.9700 |
N41A—H41A | 0.86 (2) | C6—H62B | 0.9700 |
N41A—H42A | 0.91 (2) | C2A—C3A | 1.351 (2) |
C1—C2 | 1.543 (2) | C3A—C4A | 1.418 (2) |
C1—C11 | 1.532 (2) | C4A—C5A | 1.413 (2) |
C1—C6 | 1.542 (2) | C5A—C6A | 1.348 (3) |
C2—C3 | 1.534 (2) | C2A—H2A | 0.9300 |
C2—C21 | 1.508 (2) | C3A—H3A | 0.9300 |
C3—C4 | 1.532 (3) | C5A—H5A | 0.9300 |
C4—C5 | 1.524 (3) | C6A—H6A | 0.9300 |
C5—C6 | 1.515 (3) | ||
C21—O21—H21 | 113.6 (15) | C2—C3—H31B | 109.00 |
C2A—N1A—C6A | 120.01 (16) | C2—C3—H32B | 109.00 |
C6A—N1A—H1A | 117.9 (13) | C5—C4—H41B | 109.00 |
C2A—N1A—H1A | 122.0 (13) | C5—C4—H42B | 109.00 |
H41A—N41A—H42A | 122 (2) | C3—C4—H42B | 109.00 |
C4A—N41A—H41A | 118.6 (15) | C3—C4—H41B | 109.00 |
C4A—N41A—H42A | 119.4 (13) | H41B—C4—H42B | 108.00 |
C2—C1—C6 | 109.55 (13) | C6—C5—H51B | 109.00 |
C2—C1—C11 | 114.64 (12) | C4—C5—H52B | 109.00 |
C6—C1—C11 | 110.53 (13) | C6—C5—H52B | 109.00 |
C1—C2—C21 | 112.88 (13) | H51B—C5—H52B | 108.00 |
C1—C2—C3 | 113.38 (14) | C4—C5—H51B | 109.00 |
C3—C2—C21 | 112.67 (13) | C5—C6—H62B | 109.00 |
C2—C3—C4 | 111.46 (14) | H61B—C6—H62B | 108.00 |
C3—C4—C5 | 111.52 (15) | C1—C6—H61B | 109.00 |
C4—C5—C6 | 110.92 (16) | C1—C6—H62B | 109.00 |
C1—C6—C5 | 112.68 (14) | C5—C6—H61B | 109.00 |
O11—C11—C1 | 115.58 (13) | N1A—C2A—C3A | 121.56 (17) |
O11—C11—O12 | 123.82 (14) | C2A—C3A—C4A | 120.03 (16) |
O12—C11—C1 | 120.59 (13) | N41A—C4A—C3A | 121.53 (16) |
O21—C21—C2 | 113.18 (13) | C3A—C4A—C5A | 116.50 (15) |
O22—C21—C2 | 123.99 (15) | N41A—C4A—C5A | 121.97 (15) |
O21—C21—O22 | 122.77 (15) | C4A—C5A—C6A | 120.41 (16) |
C6—C1—H1 | 107.00 | N1A—C6A—C5A | 121.50 (17) |
C2—C1—H1 | 107.00 | N1A—C2A—H2A | 119.00 |
C11—C1—H1 | 107.00 | C3A—C2A—H2A | 119.00 |
C1—C2—H2 | 106.00 | C2A—C3A—H3A | 120.00 |
C3—C2—H2 | 106.00 | C4A—C3A—H3A | 120.00 |
C21—C2—H2 | 106.00 | C4A—C5A—H5A | 120.00 |
C4—C3—H32B | 109.00 | C6A—C5A—H5A | 120.00 |
H31B—C3—H32B | 108.00 | N1A—C6A—H6A | 119.00 |
C4—C3—H31B | 109.00 | C5A—C6A—H6A | 119.00 |
C6A—N1A—C2A—C3A | −0.2 (3) | C3—C2—C21—O21 | 171.15 (14) |
C2A—N1A—C6A—C5A | 0.6 (3) | C3—C2—C21—O22 | −11.6 (2) |
C6—C1—C2—C3 | 51.98 (17) | C1—C2—C21—O21 | 41.13 (19) |
C11—C1—C2—C21 | 56.73 (18) | C1—C2—C21—O22 | −141.58 (16) |
C6—C1—C2—C21 | −178.36 (13) | C2—C3—C4—C5 | 53.7 (2) |
C11—C1—C2—C3 | −72.93 (17) | C3—C4—C5—C6 | −56.2 (2) |
C2—C1—C11—O11 | −171.66 (14) | C4—C5—C6—C1 | 57.4 (2) |
C2—C1—C11—O12 | 9.2 (2) | N1A—C2A—C3A—C4A | −0.2 (3) |
C6—C1—C11—O11 | 63.95 (18) | C2A—C3A—C4A—N41A | −179.40 (16) |
C6—C1—C11—O12 | −115.22 (16) | C2A—C3A—C4A—C5A | 0.0 (2) |
C11—C1—C6—C5 | 72.82 (18) | N41A—C4A—C5A—C6A | 179.81 (17) |
C2—C1—C6—C5 | −54.43 (19) | C3A—C4A—C5A—C6A | 0.4 (2) |
C21—C2—C3—C4 | 177.72 (15) | C4A—C5A—C6A—N1A | −0.7 (3) |
C1—C2—C3—C4 | −52.5 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1A—H1A···O12i | 0.88 (2) | 1.91 (2) | 2.795 (2) | 180 (3) |
N41A—H41A···O12ii | 0.86 (2) | 2.14 (2) | 2.989 (2) | 168 (2) |
N41A—H42A···O22 | 0.91 (2) | 2.13 (2) | 2.974 (2) | 152.6 (18) |
O21—H21···O11iii | 0.95 (3) | 1.59 (3) | 2.5302 (17) | 170 (3) |
C2A—H2A···O21iii | 0.93 | 2.46 | 3.287 (2) | 149 |
C3A—H3A···O22 | 0.93 | 2.49 | 3.225 (2) | 136 |
C3A—H3A···O11iii | 0.93 | 2.47 | 3.222 (2) | 138 |
C6A—H6A···O11iv | 0.93 | 2.38 | 3.048 (2) | 128 |
C3—H31B···O12 | 0.97 | 2.56 | 3.123 (2) | 117 |
Symmetry codes: (i) x, y, z+1; (ii) −x+1/2, y−1/2, z+1/2; (iii) −x, −y+1, z+1/2; (iv) x+1/2, −y+1/2, z+1. |
Experimental details
Crystal data | |
Chemical formula | C5H7N2+·C8H11O4− |
Mr | 266.29 |
Crystal system, space group | Orthorhombic, Pna21 |
Temperature (K) | 200 |
a, b, c (Å) | 12.1359 (3), 9.8351 (3), 11.1850 (3) |
V (Å3) | 1335.02 (6) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.30 × 0.25 × 0.20 |
Data collection | |
Diffractometer | Oxford Diffraction Gemini-S CCD-detector |
Absorption correction | Multi-scan (CrysAlis PRO; Oxford Diffraction, 2010) |
Tmin, Tmax | 0.948, 0.990 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 9670, 1709, 1448 |
Rint | 0.029 |
(sin θ/λ)max (Å−1) | 0.678 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.028, 0.060, 0.99 |
No. of reflections | 1709 |
No. of parameters | 188 |
No. of restraints | 1 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.15, −0.16 |
Computer programs: CrysAlis PRO (Oxford Diffraction, 2010), SIR92 (Altomare et al., 1994), SHELXL97 (Sheldrick, 2008) within WinGX (Farrugia, 1999), PLATON (Spek, 2009).
D—H···A | D—H | H···A | D···A | D—H···A |
N1A—H1A···O12i | 0.88 (2) | 1.91 (2) | 2.795 (2) | 180 (3) |
N41A—H41A···O12ii | 0.86 (2) | 2.14 (2) | 2.989 (2) | 168 (2) |
N41A—H42A···O22 | 0.91 (2) | 2.13 (2) | 2.974 (2) | 152.6 (18) |
O21—H21···O11iii | 0.95 (3) | 1.59 (3) | 2.5302 (17) | 170 (3) |
Symmetry codes: (i) x, y, z+1; (ii) −x+1/2, y−1/2, z+1/2; (iii) −x, −y+1, z+1/2. |
Acknowledgements
The authors acknowledge financial support from the Australian Research Council, the Faculty of Science and Technology and the University Library, Queensland University of Technology.
References
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The structures of Lewis base salts of cis-cyclohexane-1,2-dicarboxylic acid (cis-CHDC) are rare in the crystallographic literature and like the parent cis-acid (Benedetti et al., 1970), exist only in the unresolved racemic form. We have reported the structures of the 1:1 ammonium salt (Smith & Wermuth, 2011a) and the 1:1 2-aminopyridinium salt (Smith & Wermuth, 2011b) and in our parallel 1:1 stoichiometric reaction of cis-CHDC anhydride with 4-aminopyridine in 50% ethanol–water solution we also obtained minor crystals of the title compound, cis-C5H7N2+ C8H11O4- (Fig. 1) and the structure is reported here.
In the structure of the title compound, the monoanions associate through strong carboxylic acid–carboxyl O—H···O hydrogen bonds (Table 1) giving zigzag chains [graph set C(7) (Etter et al., 1990)] which extend along c (Fig. 2). The cations provide links between these chains through both pyridinium and amine N—H···Ocarboxyl hydrogen bonds, resulting in a three-dimensional structure (Figs. 2,3).