A hydrogen-bonded supramolecular complex between the chloranilic acid dianion (CA) and the 4-methyl­imidazole cation

The title salt, bis(4-methyl­imidazolium) chloranilate, 2C₄H₇N₂⁺·C₆Cl₂O₄^2-, is composed of a centrosymmetric chloranilate (CA) dianion and two 4-methyl­imidazolium cations, which are held together by inter­molecular hydrogen-bond inter­actions and ultimately construct a two-dimensional supramolecular complex.

Key indicators

• Single-crystal X-ray study
• T = 292 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.043
• wR factor = 0.113
• Data-to-parameter ratio = 14.6

checkCIF/PLATON results

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EXPT002_ALERT_1_A  _exptl_crystal_density_meas is missing, although a method
            has been given. Density measured experimentally (Mg m-3).
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Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT333_ALERT_2_C Large Average Benzene C-C Dist.  C1     -C3_a          1.44 Ang.
PLAT335_ALERT_2_C Large Benzene C-C Range          C1     -C3_a          0.16 Ang.
PLAT369_ALERT_2_C Long   C(sp2)-C(sp2) Bond  C1     -   C2     ...       1.54 Ang.

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   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
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S1. Comment

Hydrogen bonding, due to its strong directing capability of organizing molecules into supramolecular aggregates, is considered as one of the most relevant strategies for controlling molecular self-assembly during crystallization (Rodríguez-Martín et al., 2002). In recent decades, hydrogen bonds have been used to generate supramolecular assemblies and some novel related complexes have been reported (Aakeröy et al., 1998; Qin et al., 2001). Here, we report the supramolecular complex [4-methyl-imidazole]₂[CA], (I).

The complex unit of (I) consists of a CA molecule and two 2-methylimidazole molecules. The CA molecule is in the dianion state, due to losing two H atoms of the hydroxyl groups, and the 2-methylimidazole molecule is protonated in the compound (Fig. 1). Therefore, the two types of molecules are held together by a complicated hydrogen-bond network forming a supra-molecular complex, in which four O atoms of CA acting as donors and imidazoles as acceptors are linked via O—H···N hydrogen bonds (Fig. 2 and Table 1). Each O atom forms double hydrogen bonds with two adjacent imidzaoles. As shown in Fig. 2, one CA molecule interacts with six imidazoles via hydrogen bonds. In contrast, each imidazole molecule interacts with three neighbouring CA molecules, which finally build a two-dimensional supra-molecular framework.

S2. Experimental

All reagents and solvents were used as obtained without further purification. Chloranilic acid (1 mmol, 0.21 g) and 4-methylimidazole (1 mmol, 0.081 g) were dissolved in an ammonia solution (10 ml, 30%), and the mixture was stirred for about 20 min at room temperature. The resulting clear red solution was kept in air and, after slow evaporation of the solvent over a period of a week, red needle crystals of (I) formed at the bottom of the vessel.

S3. Refinement

All H atoms were located in their idealized positions, with C—H(methyl) = 0.96 Å, C—H(C5 and C6) = 0.93 Å and N—H(N1 and N2) = 0.86 Å, and included in the refinement in the riding-motion approximation, with U_iso(H) = 1.5U_eq(methyl-C) and 1.2U_eq of their carrier atoms for the other H atoms.

Computing details

Data collection: SMART (Bruker 2001); cell refinement: SAINT-Plus (Bruker 2001); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); 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 structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry code: (a) 2 − x, 1 − y, −z.]
	Fig. 2. A perspective view of the crystal packing in the unit cell, showing the linkage by hydrogen bonding (dashed lines). H atoms not involved in the hydrogen bonds have been omitted for clarity. [Symmetry codes: (a) 2 − x, 1 − y, −z; (b) 1 − x, 1 − y, −z; (c) −1/2 + x, 1/2 − y, −1/2 + z; (d) 1 + x, y, z; (e)-1 + x, y, z; (f) 1/2 + x, 1/2 − y, 1/2 + z.]

bis(4-methylimidazolium) chloranilate

Crystal data

2C4H7N2^+·C6Cl2O4^2^−	F(000) = 384
Mr = 373.20	Dx = 1.513 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 1642 reflections
a = 5.2739 (10) Å	θ = 2.5–24.6°
b = 9.5018 (17) Å	µ = 0.42 mm^−1
c = 16.560 (3) Å	T = 292 K
β = 99.157 (3)°	Block, red
V = 819.3 (3) Å^3	0.40 × 0.20 × 0.10 mm
Z = 2

Data collection

Bruker SMART APEX CCD area-detector diffractometer	1620 independent reflections
Radiation source: fine focus sealed Siemens Mo tube	1373 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
ω scans	θmax = 26.0°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −6→4
Tmin = 0.849, Tmax = 0.959	k = −11→11
4373 measured reflections	l = −18→20

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.043	H-atom parameters constrained
wR(F^2) = 0.113	w = 1/[σ^2(Fo^2) + (0.0599P)^2 + 0.1001P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
1620 reflections	Δρmax = 0.28 e Å^−3
111 parameters	Δρmin = −0.28 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.012 (2)

Special details

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.

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

	x	y	z	Uiso*/Ueq
C1	0.7109 (4)	−0.04877 (19)	0.56200 (11)	0.0315 (4)
C2	0.5207 (4)	0.06642 (19)	0.57873 (11)	0.0324 (5)
C3	0.3269 (4)	0.10803 (19)	0.51490 (11)	0.0332 (5)
C4	0.5572 (4)	0.5625 (2)	0.66397 (13)	0.0413 (5)
C5	0.3006 (4)	0.6844 (2)	0.72942 (13)	0.0452 (6)
H5	0.2195	0.7197	0.7711	0.054*
C6	0.4119 (5)	0.6480 (2)	0.61051 (13)	0.0461 (6)
H6	0.4178	0.6548	0.5548	0.055*
C7	0.7593 (5)	0.4582 (3)	0.65323 (19)	0.0680 (8)
H7A	0.6891	0.3650	0.6527	0.102*
H7B	0.8997	0.4667	0.6976	0.102*
H7C	0.8197	0.4758	0.6024	0.102*
Cl1	0.11935 (11)	0.24113 (6)	0.53649 (3)	0.0495 (3)
N1	0.4810 (4)	0.58724 (19)	0.73776 (11)	0.0453 (5)
H1	0.5416	0.5457	0.7828	0.054*
N2	0.2548 (4)	0.72288 (18)	0.65236 (11)	0.0420 (5)
H2	0.1443	0.7849	0.6318	0.050*
O1	0.8843 (3)	−0.07912 (15)	0.62053 (8)	0.0431 (4)
O2	0.5513 (3)	0.11557 (16)	0.64870 (8)	0.0471 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0328 (11)	0.0311 (10)	0.0291 (9)	0.0003 (8)	−0.0001 (8)	0.0001 (7)
C2	0.0323 (11)	0.0352 (10)	0.0287 (10)	−0.0007 (8)	0.0018 (8)	−0.0028 (8)
C3	0.0334 (11)	0.0335 (10)	0.0318 (10)	0.0074 (8)	0.0027 (8)	−0.0037 (8)
C4	0.0390 (12)	0.0377 (12)	0.0457 (12)	−0.0016 (9)	0.0020 (10)	−0.0004 (9)
C5	0.0437 (13)	0.0573 (14)	0.0339 (11)	0.0026 (11)	0.0040 (10)	0.0002 (10)
C6	0.0559 (14)	0.0488 (13)	0.0343 (11)	0.0059 (11)	0.0094 (10)	0.0045 (9)
C7	0.0573 (17)	0.0523 (15)	0.091 (2)	0.0135 (13)	0.0021 (15)	−0.0099 (14)
Cl1	0.0505 (4)	0.0525 (4)	0.0428 (4)	0.0220 (3)	−0.0011 (3)	−0.0114 (2)
N1	0.0464 (11)	0.0510 (11)	0.0338 (10)	0.0022 (9)	−0.0077 (8)	0.0101 (8)
N2	0.0425 (11)	0.0435 (10)	0.0377 (10)	0.0092 (8)	−0.0004 (8)	0.0061 (8)
O1	0.0446 (9)	0.0463 (9)	0.0336 (8)	0.0114 (7)	−0.0083 (7)	−0.0063 (6)
O2	0.0481 (10)	0.0595 (10)	0.0305 (8)	0.0128 (7)	−0.0034 (7)	−0.0151 (7)

Geometric parameters (Å, º)

C1—O1	1.256 (2)	C5—N2	1.312 (3)
C1—C3^i	1.378 (3)	C5—N1	1.317 (3)
C1—C2	1.539 (3)	C5—H5	0.9300
C2—O2	1.236 (2)	C6—N2	1.362 (3)
C2—C3	1.405 (3)	C6—H6	0.9300
C3—C1^i	1.378 (3)	C7—H7A	0.9600
C3—Cl1	1.7462 (19)	C7—H7B	0.9600
C4—C6	1.348 (3)	C7—H7C	0.9600
C4—N1	1.366 (3)	N1—H1	0.8600
C4—C7	1.486 (3)	N2—H2	0.8600
O1—C1—C3^i	126.88 (18)	C4—C6—N2	108.01 (19)
O1—C1—C2	116.09 (15)	C4—C6—H6	126.0
C3^i—C1—C2	117.04 (16)	N2—C6—H6	126.0
O2—C2—C3	124.73 (18)	C4—C7—H7A	109.5
O2—C2—C1	116.48 (16)	C4—C7—H7B	109.5
C3—C2—C1	118.79 (16)	H7A—C7—H7B	109.5
C1^i—C3—C2	124.13 (18)	C4—C7—H7C	109.5
C1^i—C3—Cl1	118.83 (15)	H7A—C7—H7C	109.5
C2—C3—Cl1	117.03 (14)	H7B—C7—H7C	109.5
C6—C4—N1	105.42 (19)	C5—N1—C4	109.73 (17)
C6—C4—C7	131.8 (2)	C5—N1—H1	125.1
N1—C4—C7	122.7 (2)	C4—N1—H1	125.1
N2—C5—N1	108.38 (19)	C5—N2—C6	108.46 (18)
N2—C5—H5	125.8	C5—N2—H2	125.8
N1—C5—H5	125.8	C6—N2—H2	125.8
O1—C1—C2—O2	−2.0 (3)	N1—C4—C6—N2	0.6 (2)
C3^i—C1—C2—O2	177.69 (19)	C7—C4—C6—N2	179.9 (2)
O1—C1—C2—C3	178.14 (18)	N2—C5—N1—C4	0.6 (3)
C3^i—C1—C2—C3	−2.2 (3)	C6—C4—N1—C5	−0.8 (3)
O2—C2—C3—C1^i	−177.5 (2)	C7—C4—N1—C5	179.9 (2)
C1—C2—C3—C1^i	2.3 (3)	N1—C5—N2—C6	−0.2 (3)
O2—C2—C3—Cl1	1.2 (3)	C4—C6—N2—C5	−0.3 (3)
C1—C2—C3—Cl1	−178.94 (13)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1^ii	0.86	1.98	2.825 (2)	167
N1—H1···O2^ii	0.86	2.36	2.867 (2)	118
N2—H2···O1^iii	0.86	1.87	2.703 (2)	162

Symmetry codes: (ii) −x+3/2, y+1/2, −z+3/2; (iii) x−1, y+1, z.