Acta Cryst. (2009). E65, o22 [ doi:10.1107/S1600536808040221 ]
In the title compound, C6H6N2O4·H2O, one carboxyl group is deprotonated and one imidazole N atom is protonated. The organic molecule, excluding methyl H atoms, is essentially planar, with an r.m.s. deviation of 0.0156 (1) Å. In the crystal structure, intermolecular N-H
O hydrogen bonds link molecules into chains along the b axis; these chains are further linked via O-HO hydrogen bonds involving the water O atoms and carboxyl O atoms, generating a two-dimensional supramolecular framework.
The title compound was synthesized according to a revised procedure (Anderson et al., 1989). 2-Methylimidazole (3.0 g) was added to a mixture of concentrated sulfuric acid (40 ml) and water (30 ml) at 363 K. This was followed by the careful addition of powdered potassium dichromate (22 g). After 30 min the mixture was poured into ice-cold water. The white precipitates were collected by filtration, and washed with water. Recrystallization from hot water afforded colorless block crystals of the title compound. Yield: 1.8 g (44%).
The carboxyl and water H atoms were located in a difference Fourier map and refined with Uiso(H) = 1.5Ueq(O). The O—H distances of the water molecule were restrained to 0.85 (1) Å; however, that of the carboxyl was refined freely. All other H-atoms were positioned geometrically and refined using a riding model with C—H (methyl) = 0.96 Å, N—H = 0.86 Å; Uiso(H) = kUeq(carrier atom), where k = 1.2 for N and 1.5 for C.
Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
![[Figure 1]](./wn2295fig1thm.gif)
| Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. Hydrogen atoms are drawn as spheres of arbitrary radius. |
![[Figure 2]](./wn2295fig2thm.gif)
| Fig. 2. Packing diagram of the title structure, showing the intermolecular N—H···O and O—H···O hydrogen bonds as dashed lines. Methyl H atoms are omitted for clarity. |
| C6H6N2O4·H2O | F(000) = 392 |
| Mr = 188.14 | Dx = 1.589 Mg m−3 |
| Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
| Hall symbol: -P 2ybc | Cell parameters from 927 reflections |
| a = 8.491 (2) Å | θ = 2.4–24.3° |
| b = 14.280 (4) Å | µ = 0.14 mm−1 |
| c = 6.5385 (17) Å | T = 295 K |
| β = 97.386 (5)° | Block, colorless |
| V = 786.2 (4) Å3 | 0.23 × 0.09 × 0.08 mm |
| Z = 4 |
| Bruker SMART APEX area-detector diffractometer | 1538 independent reflections |
| Radiation source: fine-focus sealed tube | 1246 reflections with I > 2σ(I) |
| graphite | Rint = 0.032 |
| φ and ω scans | θmax = 26.0°, θmin = 2.4° |
| Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −8→10 |
| Tmin = 0.969, Tmax = 0.995 | k = −17→17 |
| 4506 measured reflections | l = −8→7 |
| 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)] = 0.056 | Hydrogen site location: inferred from neighbouring sites |
| wR(F2) = 0.131 | H atoms treated by a mixture of independent and constrained refinement |
| S = 1.05 | w = 1/[σ2(Fo2) + (0.0559P)2 + 0.4711P] where P = (Fo2 + 2Fc2)/3 |
| 1538 reflections | (Δ/σ)max < 0.001 |
| 128 parameters | Δρmax = 0.25 e Å−3 |
| 4 restraints | Δρmin = −0.26 e Å−3 |
| C6H6N2O4·H2O | V = 786.2 (4) Å3 |
| Mr = 188.14 | Z = 4 |
| Monoclinic, P21/c | Mo Kα radiation |
| a = 8.491 (2) Å | µ = 0.14 mm−1 |
| b = 14.280 (4) Å | T = 295 K |
| c = 6.5385 (17) Å | 0.23 × 0.09 × 0.08 mm |
| β = 97.386 (5)° |
| Bruker SMART APEX area-detector diffractometer | 1538 independent reflections |
| Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 1246 reflections with I > 2σ(I) |
| Tmin = 0.969, Tmax = 0.995 | Rint = 0.032 |
| 4506 measured reflections | θmax = 26.0° |
| R[F2 > 2σ(F2)] = 0.056 | H atoms treated by a mixture of independent and constrained refinement |
| wR(F2) = 0.131 | Δρmax = 0.25 e Å−3 |
| S = 1.05 | Δρmin = −0.26 e Å−3 |
| 1538 reflections | Absolute structure: ? |
| 128 parameters | Flack parameter: ? |
| 4 restraints | Rogers parameter: ? |
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 | ||
| O1 | 0.5312 (2) | 0.88207 (11) | 0.2430 (3) | 0.0404 (5) | |
| O3 | 0.1439 (2) | 0.68027 (12) | 0.1429 (3) | 0.0430 (5) | |
| H3 | 0.191 (3) | 0.7337 (12) | 0.157 (5) | 0.065* | |
| N2 | 0.5293 (2) | 0.56877 (13) | 0.2531 (3) | 0.0287 (5) | |
| H2 | 0.5126 | 0.5094 | 0.2501 | 0.034* | |
| O2 | 0.2822 (2) | 0.83103 (12) | 0.1822 (3) | 0.0436 (5) | |
| N1 | 0.6490 (2) | 0.70121 (13) | 0.2840 (3) | 0.0284 (5) | |
| H1 | 0.7232 | 0.7424 | 0.3045 | 0.034* | |
| C2 | 0.4901 (3) | 0.72074 (15) | 0.2375 (3) | 0.0265 (5) | |
| C3 | 0.4139 (3) | 0.63632 (15) | 0.2178 (3) | 0.0265 (5) | |
| C1 | 0.4314 (3) | 0.81906 (15) | 0.2198 (4) | 0.0303 (6) | |
| C4 | 0.6708 (3) | 0.60933 (16) | 0.2927 (4) | 0.0283 (5) | |
| C5 | 0.2437 (3) | 0.61108 (17) | 0.1680 (4) | 0.0335 (6) | |
| O4 | 0.2045 (2) | 0.52952 (12) | 0.1540 (3) | 0.0506 (6) | |
| C6 | 0.8249 (3) | 0.56070 (18) | 0.3429 (4) | 0.0405 (7) | |
| H6A | 0.8557 | 0.5333 | 0.2199 | 0.061* | |
| H6B | 0.8148 | 0.5124 | 0.4425 | 0.061* | |
| H6C | 0.9043 | 0.6049 | 0.3987 | 0.061* | |
| O1W | 0.8762 (2) | 0.83332 (13) | 0.3359 (4) | 0.0563 (6) | |
| H1WA | 0.961 (3) | 0.827 (2) | 0.419 (5) | 0.084* | |
| H1WB | 0.840 (4) | 0.8884 (12) | 0.345 (5) | 0.084* |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| O1 | 0.0417 (11) | 0.0175 (8) | 0.0613 (13) | −0.0014 (7) | 0.0041 (9) | −0.0002 (8) |
| O3 | 0.0293 (10) | 0.0278 (10) | 0.0697 (14) | −0.0004 (7) | −0.0020 (9) | 0.0000 (9) |
| N2 | 0.0313 (11) | 0.0172 (9) | 0.0371 (12) | 0.0002 (8) | 0.0025 (9) | −0.0009 (8) |
| O2 | 0.0360 (11) | 0.0272 (9) | 0.0664 (14) | 0.0062 (8) | 0.0025 (9) | 0.0008 (8) |
| N1 | 0.0287 (11) | 0.0206 (10) | 0.0351 (11) | −0.0044 (8) | 0.0016 (8) | −0.0009 (8) |
| C2 | 0.0288 (12) | 0.0229 (11) | 0.0275 (13) | 0.0001 (9) | 0.0028 (10) | −0.0002 (9) |
| C3 | 0.0330 (13) | 0.0200 (11) | 0.0267 (12) | 0.0015 (9) | 0.0042 (10) | 0.0005 (9) |
| C1 | 0.0380 (14) | 0.0214 (12) | 0.0315 (14) | 0.0013 (10) | 0.0046 (10) | 0.0005 (9) |
| C4 | 0.0304 (13) | 0.0230 (12) | 0.0311 (13) | −0.0008 (9) | 0.0028 (10) | −0.0005 (9) |
| C5 | 0.0307 (13) | 0.0278 (14) | 0.0413 (15) | −0.0016 (10) | 0.0023 (11) | 0.0009 (10) |
| O4 | 0.0399 (11) | 0.0261 (10) | 0.0835 (16) | −0.0082 (8) | −0.0013 (10) | −0.0008 (9) |
| C6 | 0.0346 (14) | 0.0309 (13) | 0.0551 (18) | 0.0050 (11) | 0.0019 (12) | 0.0018 (12) |
| O1W | 0.0395 (12) | 0.0292 (10) | 0.0942 (18) | −0.0035 (8) | −0.0148 (11) | 0.0009 (11) |
| O1—C1 | 1.232 (3) | C2—C3 | 1.367 (3) |
| O3—C5 | 1.299 (3) | C2—C1 | 1.489 (3) |
| O3—H3 | 0.861 (10) | C3—C5 | 1.484 (3) |
| N2—C4 | 1.329 (3) | C4—C6 | 1.481 (3) |
| N2—C3 | 1.373 (3) | C5—O4 | 1.212 (3) |
| N2—H2 | 0.8600 | C6—H6A | 0.9600 |
| O2—C1 | 1.271 (3) | C6—H6B | 0.9600 |
| N1—C4 | 1.325 (3) | C6—H6C | 0.9600 |
| N1—C2 | 1.373 (3) | O1W—H1WA | 0.849 (10) |
| N1—H1 | 0.8600 | O1W—H1WB | 0.850 (10) |
| C5—O3—H3 | 112 (2) | O2—C1—C2 | 117.2 (2) |
| C4—N2—C3 | 109.54 (19) | N1—C4—N2 | 107.8 (2) |
| C4—N2—H2 | 125.2 | N1—C4—C6 | 126.1 (2) |
| C3—N2—H2 | 125.2 | N2—C4—C6 | 126.2 (2) |
| C4—N1—C2 | 109.81 (19) | O4—C5—O3 | 123.6 (2) |
| C4—N1—H1 | 125.1 | O4—C5—C3 | 120.0 (2) |
| C2—N1—H1 | 125.1 | O3—C5—C3 | 116.4 (2) |
| C3—C2—N1 | 106.37 (19) | C4—C6—H6A | 109.5 |
| C3—C2—C1 | 132.4 (2) | C4—C6—H6B | 109.5 |
| N1—C2—C1 | 121.2 (2) | H6A—C6—H6B | 109.5 |
| C2—C3—N2 | 106.5 (2) | C4—C6—H6C | 109.5 |
| C2—C3—C5 | 132.1 (2) | H6A—C6—H6C | 109.5 |
| N2—C3—C5 | 121.3 (2) | H6B—C6—H6C | 109.5 |
| O1—C1—O2 | 125.4 (2) | H1WA—O1W—H1WB | 110 (2) |
| O1—C1—C2 | 117.4 (2) | ||
| C4—N1—C2—C3 | 0.1 (3) | C3—C2—C1—O2 | 1.2 (4) |
| C4—N1—C2—C1 | 179.5 (2) | N1—C2—C1—O2 | −178.0 (2) |
| N1—C2—C3—N2 | 0.0 (2) | C2—N1—C4—N2 | −0.1 (3) |
| C1—C2—C3—N2 | −179.3 (2) | C2—N1—C4—C6 | −178.7 (2) |
| N1—C2—C3—C5 | −179.6 (2) | C3—N2—C4—N1 | 0.1 (3) |
| C1—C2—C3—C5 | 1.1 (4) | C3—N2—C4—C6 | 178.7 (2) |
| C4—N2—C3—C2 | −0.1 (3) | C2—C3—C5—O4 | 178.1 (3) |
| C4—N2—C3—C5 | 179.6 (2) | N2—C3—C5—O4 | −1.4 (4) |
| C3—C2—C1—O1 | −178.9 (2) | C2—C3—C5—O3 | −2.3 (4) |
| N1—C2—C1—O1 | 1.9 (3) | N2—C3—C5—O3 | 178.2 (2) |
| D—H···A | D—H | H···A | D···A | D—H···A |
| O1W—H1WB···O4i | 0.85 (1) | 2.05 (1) | 2.887 (3) | 168 (4) |
| O1W—H1WA···O3ii | 0.85 (1) | 2.00 (1) | 2.839 (3) | 173 (4) |
| N2—H2···O1iii | 0.86 | 1.86 | 2.716 (3) | 176 |
| N1—H1···O1W | 0.86 | 1.83 | 2.689 (3) | 177 |
| O3—H3···O2 | 0.86 (1) | 1.59 (2) | 2.447 (2) | 179 (3) |
| Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) x+1, −y+3/2, z+1/2; (iii) −x+1, y−1/2, −z+1/2. |
| D—H···A | D—H | H···A | D···A | D—H···A |
| O1W—H1WB···O4i | 0.85 (1) | 2.05 (1) | 2.887 (3) | 168 (4) |
| O1W—H1WA···O3ii | 0.85 (1) | 2.00 (1) | 2.839 (3) | 173 (4) |
| N2—H2···O1iii | 0.86 | 1.86 | 2.716 (3) | 176 |
| N1—H1···O1W | 0.86 | 1.83 | 2.689 (3) | 177 |
| O3—H3···O2 | 0.86 (1) | 1.59 (2) | 2.447 (2) | 179 (3) |
| Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) x+1, −y+3/2, z+1/2; (iii) −x+1, y−1/2, −z+1/2. |
The author thanks Jiangxi Science and Technology Normal University for supporting this study.
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In recent years, N-heterocyclic carboxylic acids have attracted considerable interest as ligands in metal complexes because of their structural diversity (Nie et al., 2007; Sun et al.) and their potential applications as functional materials (Liang et al., 2002; Qin et al., 2002; Li et al., 1998). Sun et al. (2006) have prepared the inner salt, 4-carboxy-2-(pyridinium-4-yl)-1H-imidazole-5-carboxylate monohydrate; in its crystal structure, one carboxyl group is deprotonated and the pyridyl group is protonated. Nie et al. (2007) have reported the mononuclear complex, diaquabis(5-carboxy-2-methyl-1H-imidazole-4-carboxylate- κ2N3,O4)cadmium(II). Imidazole derivatives have a wide range of biological activities such as analgesic (Ucucu et al., 2001), anti-inflammatory (Maeda et al., 1984), antiparasitic (Quattara et al., 1987), antiepileptic and platelet aggregation inhibitors (Seko et al., 1991). I report here the crystal structure of 4-carboxy-2-methyl-1H-3-imidazolium-5-carboxylate monohydrate.
As shown in Fig. 1, the asymmetric unit consists of a neutral C6H6N2O4 molecule and one water molecule. The organic molecule, excluding methyl hydrogen atoms, is essentially planar, with an r.m.s. deviation of 0.0156 (1) Å. The C1-containing carboxylate group forms an intramolecular hydrogen bond with the neighboring C5-containing carboxyl group.
In the crystal structure, intermolecular N—H···O hydrogen bonds link the molecules into chains along the b axis; these chains are further linked via O—H···O hydrogen bonds involving the water O atoms and carboxyl O atoms, generating a two-dimensional supramolecular framework (Fig. 2).