research communications
Hydrogen-bonded network in the salt 4-methyl-1H-imidazol-3-ium picrate
aCollege of Chemistry, Central China Normal University, Wuhan 430079, People's Republic of China
*Correspondence e-mail: xingman_xu@126.com
In the title molecular salt, C4H7N2+·C6H2N3O7−, the phenolic proton of the starting picric acid has been transferred to the imidazole N atom. The nitro groups are twisted away from the benzene ring plane, making dihedral angles of 12.8 (2), 9.2 (4) and 29.3 (2)°. In the crystal, the component ions are linked into chains along [010] via N—H⋯O and bifurcated N—H⋯(O,O) hydrogen bonds. These chains are further linked by weak C—H⋯O hydrogen bonds into a three-dimensional network. The complex three-dimensional network can be topologically simplified into a 4-connected uninodal net with the point symbol {4.85}.
Keywords: crystal structure; salt; 4-methyimidazole; picric acid; uninodal {42.85} net.
CCDC reference: 1476728
1. Chemical context
Co-crystallization, the crystallization of more than one solid component into a new compound, forming a new et al., 2015; Weyna et al., 2012; Robinson, 2010; Arenas-García et al., 2010) and crystal engineering (Manoj et al., 2014). 4-Methylimidazole is an often used pharmaceutical intermediate (Shimpi et al., 2014). The study of its crystallization can facilitate its related organic synthesis and theoretical optimization calculations. Picric acid, as a strong organic proton-donating reagent, is often adopted 2as an organic acid in the synthesis of co-crystallized complexes. Herein, we report the of the molecular salt, 4-methylimidazolium picrate, (I). Future work will concentrate on how the crystallization behavior is affected by the solvent and temperature.
or molecular salt, is a well known research field involving, for example, active pharmaceutical ingredients (Aitipamula2. Structural commentary
The consists of one 4-methylimidazolium cation and one picrate anion (Fig. 1). The phenolic proton in the original picric acid starting material was transferred from the picric acid OH group to the imidazole nitrogen atom, forming a molecular salt. In the picrate anion, the C—Ophenol bond distance is shorter than in an earlier reported un-deprotonated compound [1.33 (2) Å; Bertolasi et al., 2011] with a value of 1.244 (2) Å in (I). The adjacent C1—C2 [1.453 (2) Å] and C1—C6 [1.457 (3) Å] bonds are also lengthened from the values expected in a completely delocalized benzene ring. The C2—C1—C6 angle [111.0 (2)°] is smaller by ca 10° than the average value of the other five phenyl inner angles [121.8 (1)°]. This is mainly due to the electron-withdrawing effect of the three nitro groups attached to the aromatic π system, delocalizing electron density on the phenolate oxygen atom over the π system. The three nitro groups, N1/O2/O3, N2/O4/O5 and N3/O6/O6, are twisted away from the benzene ring plane, making dihedral angles of 12.8 (2), 9.2 (4) and 29.3 (2)°, respectively. In the 4-methylimidazolium cation, the C9—N4 [1.321 (3) Å] and C9—N5 [1.304 (3) Å] bond lengths are similar to each other due to the delocalizing effect; this is in contrast to the un-protonated 4-methylimidazole molecule in the of 8-hydroxyquinoline and 5-methyl-1H-imidazole [C—N = 1.305 (4) and 1.340 4 Å; Liu & Meng, 2006].
of (I)3. Supramolecular features
In the , the component ions are linked into chains along [010] by N—H⋯O hydrogen bonds (Table 1, Fig. 2), one of which is bifurcated, N—H⋯(O,O). The chains are linked by C—H⋯O interactions, forming a three-dimensional framework. In the cation, all H atoms except for the methyl group H atoms act as hydrogen-bond donors. Each cation is bonded to four adjacent picrate anions. In turn, each picrate anion utilizes the one phenolic and four nitro oxygen atoms, acting as hydrogen-bond acceptors, linked to four 4-methylimidazolium cations. No other interactions such as π–π and C—H⋯π are observed (Spek, 2009).
of (I)In order to better understand the three-dimensional structure, we can regard both the cation and anion as 4-connected nodes (Fig. 3), i.e. each one 4-methylimidazolium ion links with four other picrate ions, and vice versa. Thus, the whole network is simplified into a uninodal 4-connected net with the point symbol {4.85} (Baburin & Blatov, 2007; Blatov et al., 2014) (Fig. 4).
4. Database survey
A CSD search (CSD Version 5.37 plus one update; Groom et al., 2016) found some analogs of the title compound, viz. BEZGEU (2-methylimidazolium picrate 2-methylimidazole; Dhanabal et al., 2013) and QAKYOS (2-methyl-1H-imidazol-3-ium 2,4,6-trinitrophenolate; Dutkiewicz et al., 2011). A structural comparison indicates that the two nitrogen atoms are preferably hydrogen-bonded to the picrate anions, of which one is bifurcated and the other is linear.
5. Synthesis and crystallization
Equivalent molar amounts of 4-methyl imidazole (1.0 mmol, 80.0 mg) and picric acid (1 mmol, 230.0mg) were dissolved in 95% methanol (40.0 ml). The mixture was stirred for half an hour at room temperature and then filtered. The resulting yellow solution was kept in air for two weeks. Needle-shaped yellow crystals of (I) suitable for single-crystal X-ray were grown at the bottom of the vessel by slow evaporation of the solution. The crystals were separated by filtration (yield, 75%, ca 0.23 g).
6. Refinement
Crystal data, data collection and structure . H atoms bonded to C atoms were positioned geometrically with C—H = 0.93 Å (aromatic) or 0.96 Å (methyl) and refined using a riding model [Uiso(H) = 1.2Ueq(Caromatic) or 1.5Ueq(Cmethyl)]. H atoms bonded to N atoms were found in Fourier difference maps; N—H distances were refined freely with Uiso(H) = 1.2Ueq(N).
details are summarized in Table 2
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Supporting information
CCDC reference: 1476728
https://doi.org/10.1107/S205698901600712X/lh5809sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S205698901600712X/lh5809Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S205698901600712X/lh5809Isup3.cml
Data collection: SMART (Bruker, 2001); cell
SAINT-Plus (Bruker, 2001); data reduction: SAINT-Plus (Bruker, 2001); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C4H7N2+·C6H2N3O7− | F(000) = 640 |
Mr = 311.22 | Dx = 1.628 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 9.3079 (17) Å | Cell parameters from 1754 reflections |
b = 9.4339 (17) Å | θ = 2.3–22.1° |
c = 15.195 (3) Å | µ = 0.14 mm−1 |
β = 107.835 (2)° | T = 298 K |
V = 1270.2 (4) Å3 | Needle, yellow |
Z = 4 | 0.30 × 0.05 × 0.02 mm |
Bruker SMART CCD diffractometer | 1539 reflections with I > 2σ(I) |
φ and ω scans | Rint = 0.142 |
Absorption correction: multi-scan (SADABS; Sheldrick, 2008) | θmax = 26.0°, θmin = 2.3° |
Tmin = 0.936, Tmax = 0.992 | h = −11→11 |
12952 measured reflections | k = −11→11 |
2489 independent reflections | l = −18→18 |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.052 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.110 | w = 1/[σ2(Fo2) + (0.0154P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
2489 reflections | Δρmax = 0.25 e Å−3 |
206 parameters | Δρmin = −0.22 e Å−3 |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.1017 (2) | 0.4075 (2) | 0.43900 (15) | 0.0339 (6) | |
C2 | 0.0815 (2) | 0.3083 (2) | 0.50742 (14) | 0.0340 (6) | |
C3 | −0.0320 (2) | 0.2096 (2) | 0.49046 (15) | 0.0350 (6) | |
H3 | −0.0386 | 0.1486 | 0.5371 | 0.042* | |
C4 | −0.1356 (2) | 0.2015 (2) | 0.40413 (15) | 0.0318 (5) | |
C5 | −0.1265 (2) | 0.2912 (2) | 0.33388 (15) | 0.0344 (6) | |
H5 | −0.1983 | 0.2860 | 0.2759 | 0.041* | |
C6 | −0.0126 (2) | 0.3863 (2) | 0.34989 (14) | 0.0326 (6) | |
C7 | 0.4896 (2) | 0.7421 (2) | 0.51495 (15) | 0.0367 (6) | |
C8 | 0.6087 (3) | 0.8040 (3) | 0.57572 (16) | 0.0420 (6) | |
H8 | 0.6633 | 0.8808 | 0.5646 | 0.050* | |
C9 | 0.5366 (3) | 0.6298 (3) | 0.64773 (16) | 0.0438 (7) | |
H9 | 0.5314 | 0.5658 | 0.6932 | 0.053* | |
C10 | 0.4074 (3) | 0.7745 (3) | 0.41634 (16) | 0.0552 (7) | |
H10A | 0.3094 | 0.8119 | 0.4116 | 0.083* | |
H10B | 0.3966 | 0.6894 | 0.3803 | 0.083* | |
H10C | 0.4634 | 0.8432 | 0.3936 | 0.083* | |
N1 | 0.1822 (2) | 0.3139 (2) | 0.60151 (13) | 0.0421 (5) | |
N2 | −0.2537 (2) | 0.0971 (2) | 0.38594 (15) | 0.0414 (5) | |
N3 | −0.0051 (3) | 0.4734 (2) | 0.27120 (13) | 0.0438 (5) | |
N4 | 0.4464 (2) | 0.6333 (2) | 0.56162 (13) | 0.0390 (5) | |
H4A | 0.369 (3) | 0.584 (3) | 0.5399 (16) | 0.047* | |
N5 | 0.6343 (2) | 0.7322 (2) | 0.65746 (14) | 0.0450 (6) | |
H5A | 0.706 (3) | 0.757 (3) | 0.7063 (18) | 0.054* | |
O1 | 0.19859 (18) | 0.50281 (17) | 0.45332 (11) | 0.0487 (5) | |
O2 | 0.2988 (2) | 0.3814 (2) | 0.62018 (11) | 0.0623 (6) | |
O3 | 0.1436 (2) | 0.2490 (2) | 0.66125 (12) | 0.0682 (6) | |
O4 | −0.2498 (2) | 0.00651 (19) | 0.44540 (13) | 0.0600 (5) | |
O5 | −0.35582 (18) | 0.10262 (18) | 0.31206 (12) | 0.0520 (5) | |
O6 | −0.1232 (2) | 0.4962 (2) | 0.21012 (13) | 0.0744 (6) | |
O7 | 0.1172 (2) | 0.5136 (2) | 0.26798 (12) | 0.0673 (6) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0342 (14) | 0.0300 (14) | 0.0336 (13) | 0.0044 (11) | 0.0044 (11) | −0.0040 (11) |
C2 | 0.0361 (13) | 0.0374 (14) | 0.0223 (12) | 0.0054 (11) | 0.0001 (10) | −0.0027 (10) |
C3 | 0.0416 (14) | 0.0332 (13) | 0.0295 (14) | 0.0067 (11) | 0.0100 (11) | 0.0010 (11) |
C4 | 0.0311 (13) | 0.0310 (13) | 0.0318 (13) | −0.0012 (11) | 0.0074 (11) | −0.0043 (11) |
C5 | 0.0373 (13) | 0.0358 (13) | 0.0245 (12) | 0.0039 (11) | 0.0010 (10) | −0.0043 (11) |
C6 | 0.0389 (14) | 0.0296 (13) | 0.0262 (12) | 0.0024 (11) | 0.0055 (10) | 0.0018 (10) |
C7 | 0.0410 (15) | 0.0341 (14) | 0.0313 (14) | 0.0045 (11) | 0.0056 (11) | −0.0018 (11) |
C8 | 0.0456 (15) | 0.0401 (15) | 0.0371 (15) | −0.0006 (12) | 0.0080 (12) | −0.0018 (12) |
C9 | 0.0514 (17) | 0.0405 (15) | 0.0329 (15) | 0.0040 (13) | 0.0030 (13) | 0.0019 (11) |
C10 | 0.0690 (18) | 0.0555 (18) | 0.0323 (15) | 0.0077 (15) | 0.0023 (13) | 0.0037 (13) |
N1 | 0.0473 (13) | 0.0444 (14) | 0.0281 (12) | 0.0037 (11) | 0.0020 (10) | −0.0017 (10) |
N2 | 0.0427 (13) | 0.0394 (13) | 0.0421 (13) | 0.0010 (10) | 0.0131 (11) | −0.0065 (11) |
N3 | 0.0503 (14) | 0.0377 (13) | 0.0349 (12) | −0.0030 (11) | 0.0007 (11) | 0.0058 (10) |
N4 | 0.0366 (12) | 0.0352 (12) | 0.0353 (12) | −0.0032 (10) | −0.0033 (10) | −0.0046 (9) |
N5 | 0.0415 (13) | 0.0515 (14) | 0.0306 (12) | 0.0014 (11) | −0.0058 (10) | −0.0104 (11) |
O1 | 0.0515 (11) | 0.0442 (11) | 0.0398 (10) | −0.0130 (9) | −0.0017 (8) | −0.0003 (8) |
O2 | 0.0481 (11) | 0.0838 (16) | 0.0408 (11) | −0.0196 (11) | −0.0074 (9) | 0.0005 (10) |
O3 | 0.0797 (14) | 0.0853 (15) | 0.0274 (10) | −0.0219 (12) | −0.0016 (10) | 0.0122 (10) |
O4 | 0.0664 (13) | 0.0493 (12) | 0.0609 (13) | −0.0107 (10) | 0.0144 (10) | 0.0134 (10) |
O5 | 0.0459 (11) | 0.0590 (13) | 0.0428 (11) | −0.0098 (9) | 0.0014 (9) | −0.0118 (9) |
O6 | 0.0702 (14) | 0.0825 (15) | 0.0472 (12) | −0.0069 (11) | −0.0163 (10) | 0.0287 (11) |
O7 | 0.0618 (13) | 0.0821 (15) | 0.0546 (12) | −0.0132 (12) | 0.0126 (10) | 0.0241 (11) |
C1—O1 | 1.244 (2) | C8—H8 | 0.9300 |
C1—C2 | 1.453 (3) | C9—N5 | 1.304 (3) |
C1—C6 | 1.457 (3) | C9—N4 | 1.321 (3) |
C2—C3 | 1.372 (3) | C9—H9 | 0.9300 |
C2—N1 | 1.451 (3) | C10—H10A | 0.9600 |
C3—C4 | 1.372 (3) | C10—H10B | 0.9600 |
C3—H3 | 0.9300 | C10—H10C | 0.9600 |
C4—C5 | 1.385 (3) | N1—O2 | 1.214 (2) |
C4—N2 | 1.438 (3) | N1—O3 | 1.236 (2) |
C5—C6 | 1.353 (3) | N2—O5 | 1.230 (2) |
C5—H5 | 0.9300 | N2—O4 | 1.236 (2) |
C6—N3 | 1.470 (3) | N3—O7 | 1.215 (2) |
C7—C8 | 1.340 (3) | N3—O6 | 1.222 (2) |
C7—N4 | 1.375 (3) | N4—H4A | 0.84 (2) |
C7—C10 | 1.491 (3) | N5—H5A | 0.87 (2) |
C8—N5 | 1.370 (3) | ||
O1—C1—C2 | 125.9 (2) | N5—C9—N4 | 107.6 (2) |
O1—C1—C6 | 123.1 (2) | N5—C9—H9 | 126.2 |
C2—C1—C6 | 111.0 (2) | N4—C9—H9 | 126.2 |
C3—C2—N1 | 116.0 (2) | C7—C10—H10A | 109.5 |
C3—C2—C1 | 124.3 (2) | C7—C10—H10B | 109.5 |
N1—C2—C1 | 119.7 (2) | H10A—C10—H10B | 109.5 |
C4—C3—C2 | 119.5 (2) | C7—C10—H10C | 109.5 |
C4—C3—H3 | 120.2 | H10A—C10—H10C | 109.5 |
C2—C3—H3 | 120.2 | H10B—C10—H10C | 109.5 |
C3—C4—C5 | 120.8 (2) | O2—N1—O3 | 121.9 (2) |
C3—C4—N2 | 119.6 (2) | O2—N1—C2 | 120.7 (2) |
C5—C4—N2 | 119.6 (2) | O3—N1—C2 | 117.4 (2) |
C6—C5—C4 | 119.8 (2) | O5—N2—O4 | 122.5 (2) |
C6—C5—H5 | 120.1 | O5—N2—C4 | 118.5 (2) |
C4—C5—H5 | 120.1 | O4—N2—C4 | 118.9 (2) |
C5—C6—C1 | 124.5 (2) | O7—N3—O6 | 123.5 (2) |
C5—C6—N3 | 117.02 (19) | O7—N3—C6 | 119.07 (19) |
C1—C6—N3 | 118.4 (2) | O6—N3—C6 | 117.4 (2) |
C8—C7—N4 | 106.3 (2) | C9—N4—C7 | 109.4 (2) |
C8—C7—C10 | 131.6 (2) | C9—N4—H4A | 125.9 (17) |
N4—C7—C10 | 122.1 (2) | C7—N4—H4A | 124.4 (17) |
C7—C8—N5 | 106.6 (2) | C9—N5—C8 | 110.0 (2) |
C7—C8—H8 | 126.7 | C9—N5—H5A | 128.9 (17) |
N5—C8—H8 | 126.7 | C8—N5—H5A | 121.1 (17) |
D—H···A | D—H | H···A | D···A | D—H···A |
N4—H4A···O2 | 0.84 (2) | 2.46 (2) | 3.013 (3) | 124 (2) |
N4—H4A···O1 | 0.84 (2) | 1.88 (2) | 2.687 (2) | 160 (2) |
N5—H5A···O3i | 0.87 (2) | 2.07 (3) | 2.898 (3) | 160 (2) |
C8—H8···O4ii | 0.93 | 2.50 | 3.302 (3) | 145 |
C9—H9···O5iii | 0.93 | 2.39 | 3.242 (3) | 152 |
Symmetry codes: (i) −x+1, y+1/2, −z+3/2; (ii) x+1, y+1, z; (iii) x+1, −y+1/2, z+1/2. |
Acknowledgements
We thank Dr Xiang-gao Meng for helpful discussions about this crystal structure.
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