Crystal structure of 2-methyl-1H-imidazol-3-ium hydrogen oxalate dihydrate.

Single crystals of the title mol-ecular salt, C4H7N2 (+)·HC2O4 (-)·2H2O, were isolated from the reaction of 2-methyl-1H-imidazole and oxalic acid in a 1:1 molar ratio in water. In the crystal, the cations and anions are positioned alternately along an infinite [010] ribbon and linked together through bifurcated N-H⋯(O,O) hydrogen bonds. The water mol-ecules of crystallization link the chains into (10-1) bilayers, with the methyl groups of the cations organized in an isotactic manner.

Chemical context

Imidazolium-type building blocks are useful in the field of crystal engineering (MacDonald et al., 2001 ▸). With many possibilities of substitution (involving various positions around the five-membered ring) and via the propagation of multidirectional hydrogen-bonding inter­actions, they easily lead to the self-assembly of poly-dimensional packing net­works. In 2010, Callear and co-workers described various topologies based on imidazolium/di­carb­oxy­lic acid combinations and showed the crystal-packing effects of substitution in the imidazole ring (Callear et al., 2010 ▸). In this context, and for some time, our group has focused on the contribution of the 2-methyl­imidazolium cation as a co-crystal in organic (Diop, Diop & Maris, 2016 ▸) and organic–inorganic hybrid salts (Diop, Diop & Maris, 2015 ▸; Diop, Diop, Plasseraud & Maris, 2015 ▸, 2016 ▸). Continuing our ongoing studies in this field, we report herein the crystal structure of a new hydrated organic salt, namely 2-methyl-1H-imidazol-3-ium hydrogen oxalate dihydrate, (I), isolated by reacting 2-methyl-1H-imidazole and oxalic acid in a 1:1 molar ratio in water.

Structural comments

The asymmetric unit of the title molecular salt (I) consists of four components, i.e. one 2-methyl-1H-imidazol-3-ium cation, one hydrogen oxalate anion and two solvent water mol­ecules (Fig. 1 ▸). The hydrogen oxalate anion is slightly twisted, with O1—C6—C5—O3 and O2—C6—C5—O4 torsion angles of 6.9 (3) and 7.3 (3)°, respectively. The C5—O3 and C5—O4 bonds are almost equal in length [1.249 (2) and 1.245 (2) Å, respectively], whereas C6—O2 is typical for a >C=O group [1.206 (2) Å] and C6—O1 has a normal C—OH bond length [1.306 (2) Å] (Adams, 1978 ▸).

Figure 1

The mol­ecular structure of (I), showing the atom labelling. Displacement ellipsoids are draw at the 50% probability level.

Supra­molecular features

Hydrogen-bonding inter­actions are listed in Table 1 ▸ and illustrated in Fig. 2 ▸. Both N—H groups of the imidazolium cation are involved in asymmetric bifurcated N—H⋯(O,O) hydrogen bonds with two distinct neighbouring hydrogen oxalate anions, which initiates the propagation of an infinite ribbon along the b-axis direction. Considering the orientation of the methyl groups of the cations along the ribbon, the sequence can be described as ‘isotactic’. The cations and anions are positioned alternately and are almost coplanar [dihedral angle between adjacent species = 1.15 (9)°].

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O3	0.88	1.94	2.811 (2)	172
N1—H1⋯O1	0.88	2.50	2.991 (2)	116
N2—H2⋯O4i	0.88	1.97	2.842 (2)	169
N2—H2⋯O2i	0.88	2.49	2.977 (2)	116
O1—H1A⋯O5	0.84	1.69	2.5234 (19)	169
O6—H6A⋯O2ii	0.85	2.02	2.7893 (19)	150
O6—H6B⋯O3iii	0.85	1.87	2.700 (2)	166
O5—H5A⋯O6	0.85	1.82	2.672 (2)	176
O5—H5B⋯O4iv	0.85	1.88	2.720 (2)	167

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) .

Figure 2

The crystal packing of the title salt, showing a two-dimensional bilayer-like arrangement through N—H⋯(O,O) and O—H⋯O inter­actions. H atoms not involved in hydrogen bonding have been omitted for clarity. Colour code: C dark grey, H light grey, O red and N blue.

As well as the cation-to-anion links, the OH group of the anion acts as a hydrogen-bond donor with one mol­ecule of water, which is also the donor for hydrogen-bond inter­actions with (i) a second mol­ecule of water and (ii) an O atom of a hydrogen oxalate anion involved in a neighbouring ribbon. The second water mol­ecule also bridges two distinct hydrogen oxalate anions through two O—H⋯O hydrogen bonds. Thus, all the O atoms of the hydrogen oxalate anions are involved in the hydrogen-bonding network.

The supra­molecular arrangement depicted in Fig. 2 ▸ relies on the contributions of the four components of (I) and can be described as resulting from three levels of organization: (i) C4H7N2 + and HC2O4 − assembled in infinite ribbons; (ii) parallel ribbons of C4H7N2 +/HC2O4 − connected together by water mol­ecules, which leads to a staircase–sheet structure; (iii) sheets stacked in pairs which can be described as a two-dimensional bilayer-like arrangement propagating in (10). This final organization is again induced by the formation of hydrogen-bonding inter­actions between the water mol­ecules contained in each sheet. The inter-sheet distance is about 3.4 Å. Inter­estingly, all the methyl substituents of the imidazolium rings are oriented in the same direction along the c axis. Thus, the isotacticity observed at the ribbon level is also extended across the supra­molecular network.

Database survey

To date, 176 structures of hydrogen oxalates have been deposited in the Cambridge Structural Database (CSD; Groom et al., 2016 ▸). Among these, five hits describe imidazolium salts or derivatives, i.e. imidazolium hydrogen oxalate [CSD refcodes MEQPAZ (MacDonald et al., 2001 ▸) and MEQPAZ01 (Prasad et al., 2002 ▸)], (S)-(+)-2-[2-(biphenyl-2-yl)-1-methyl­eth­yl]-4,5-di­hydro-1H-imidazolium hydrogen ox­alate (GAQTOI; Giannella et al., 2005 ▸), 1,3-diisopropyl-4,5-di­methyl­imidazolium hydrogen oxalate (DOHTOK; Abu-Rayyan et al., 2008 ▸), (S)-(−)-6-(4-bromo­phen­yl)-2,3,5,6-tetra­hydro­thia­zolo[2,3-b]imidazolium hydrogen oxalate (ROF­QAF; Minor & Chruszcz, 2008 ▸).

Synthesis and crystallization

Equimolar solutions of 2-methyl-1H-imidazole (6.51 g, 79.39 mmol) and H2C2O4·2H2O (10.00 g, 79.39 mmol) in water (100 ml) were mixed together at room temperature (301 K). Needle-shaped colourless crystals of (I) were obtained after one week by evaporation of the solvent at 333 K (yield 10.83 g, 65.5%).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All H atoms on C, O and N atoms were placed at calculated positions using a riding model, with aromatic C—H = 0.95 Å and aromatic N—H = 0.88 Å, and with U iso(H) = 1.2U eq(C,N), or hy­droxy O—H = 0.84 Å, water O—H = 0.85 Å and methyl C—H = 0.98 Å, and with U iso(H) = 1.5U eq(O,C).

Table 2

Experimental details

Crystal data
Chemical formula	C4H7N2 +·C2HO4 −·2H2O
M r	208.18
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	115
a, b, c (Å)	6.7139 (7), 9.5116 (7), 15.2115 (13)
β (°)	101.151 (6)
V (Å3)	953.07 (15)
Z	4
Radiation type	Mo Kα
μ (mm−1)	0.13
Crystal size (mm)	0.30 × 0.10 × 0.08
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2014 ▸)
T min, T max	0.691, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	15445, 2187, 1258
R int	0.063
(sin θ/λ)max (Å−1)	0.650
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.043, 0.115, 1.01
No. of reflections	2187
No. of parameters	135
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.40, −0.23

Computer programs: APEX2 and SAINT (Bruker, 2013 ▸), SHELXS2013 (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸) and OLEX2 (Dolomanov et al., 2009 ▸).

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2056989016011038/hb7595sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016011038/hb7595Isup2.hkl

Click here for additional data file.

Supporting information file. DOI: 10.1107/S2056989016011038/hb7595Isup3.cml

CCDC reference: 1491387

Additional supporting information: crystallographic information; 3D view; checkCIF report

C4H7N2+·C2HO4−·2H2O	F(000) = 440
Mr = 208.18	Dx = 1.451 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 6.7139 (7) Å	Cell parameters from 2578 reflections
b = 9.5116 (7) Å	θ = 3.5–26.4°
c = 15.2115 (13) Å	µ = 0.13 mm−1
β = 101.151 (6)°	T = 115 K
V = 953.07 (15) Å3	Needle, colourless
Z = 4	0.30 × 0.10 × 0.08 mm

Bruker APEXII CCD diffractometer	2187 independent reflections
Radiation source: X-ray tube, Siemens KFF Mo 2K-90C	1258 reflections with I > 2σ(I)
TRIUMPH curved crystal monochromator	Rint = 0.063
Detector resolution: 1024 x 1024 pixels mm-1	θmax = 27.5°, θmin = 2.5°
φ and ω scans'	h = −8→8
Absorption correction: multi-scan SADABS (Bruker, 2014) was used for absorption correction. wR2(int) was 0.0622 before and 0.0548 after correction. The Ratio of minimum to maximum transmission is 0.9269. The λ/2 correction factor is 0.00150.	k = −12→12
Tmin = 0.691, Tmax = 0.746	l = −19→19
15445 measured reflections

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.043	H-atom parameters constrained
wR(F2) = 0.115	w = 1/[σ2(Fo2) + (0.0448P)2 + 0.3824P] where P = (Fo2 + 2Fc2)/3
S = 1.01	(Δ/σ)max < 0.001
2187 reflections	Δρmax = 0.40 e Å−3
135 parameters	Δρmin = −0.23 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
O4	0.3344 (2)	0.84241 (13)	0.62704 (8)	0.0224 (3)
O3	0.3377 (2)	0.60714 (13)	0.62300 (9)	0.0247 (3)
O1	0.1928 (2)	0.60978 (13)	0.44891 (9)	0.0254 (4)
H1A	0.1572	0.6196	0.3932	0.038*
O6	0.3979 (2)	0.45757 (14)	0.22494 (10)	0.0314 (4)
H6A	0.3724	0.3954	0.1842	0.047*
H6B	0.4883	0.4270	0.2677	0.047*
O2	0.2253 (2)	0.84212 (14)	0.44546 (9)	0.0311 (4)
O5	0.1121 (3)	0.61142 (17)	0.27986 (9)	0.0357 (4)
H5A	0.1986	0.5615	0.2599	0.054*
H5B	0.0183	0.6360	0.2367	0.054*
N2	0.2719 (2)	0.11229 (16)	0.54620 (11)	0.0231 (4)
H2	0.2824	0.0244	0.5647	0.028*
N1	0.2803 (2)	0.33729 (17)	0.54697 (11)	0.0245 (4)
H1	0.2970	0.4248	0.5657	0.029*
C5	0.3089 (3)	0.7264 (2)	0.58854 (12)	0.0186 (4)
C6	0.2361 (3)	0.7327 (2)	0.48607 (12)	0.0187 (4)
C1	0.3139 (3)	0.2239 (2)	0.59833 (14)	0.0244 (5)
C2	0.2138 (3)	0.2951 (2)	0.45809 (14)	0.0287 (5)
H2A	0.1789	0.3549	0.4074	0.034*
C4	0.3880 (3)	0.2233 (2)	0.69571 (13)	0.0291 (5)
H4A	0.3300	0.1428	0.7222	0.044*
H4B	0.3472	0.3106	0.7215	0.044*
H4C	0.5364	0.2160	0.7085	0.044*
C3	0.2088 (3)	0.1547 (2)	0.45810 (14)	0.0296 (5)
H3	0.1696	0.0954	0.4075	0.036*

	U11	U22	U33	U12	U13	U23
O4	0.0311 (8)	0.0146 (7)	0.0198 (7)	−0.0010 (6)	0.0005 (6)	−0.0023 (6)
O3	0.0375 (9)	0.0141 (7)	0.0196 (7)	0.0018 (6)	−0.0018 (6)	0.0018 (6)
O1	0.0417 (10)	0.0159 (7)	0.0160 (7)	−0.0014 (6)	−0.0010 (7)	−0.0013 (5)
O6	0.0439 (11)	0.0223 (8)	0.0224 (8)	0.0083 (7)	−0.0075 (7)	−0.0045 (6)
O2	0.0568 (11)	0.0135 (7)	0.0203 (8)	−0.0004 (7)	0.0009 (7)	0.0024 (6)
O5	0.0412 (11)	0.0421 (10)	0.0201 (8)	0.0125 (8)	−0.0030 (7)	−0.0046 (7)
N2	0.0282 (10)	0.0116 (8)	0.0285 (10)	−0.0004 (7)	0.0026 (8)	0.0012 (7)
N1	0.0280 (10)	0.0128 (8)	0.0322 (10)	0.0004 (7)	0.0043 (8)	−0.0006 (7)
C5	0.0192 (11)	0.0153 (9)	0.0200 (10)	0.0020 (8)	0.0010 (8)	0.0006 (8)
C6	0.0198 (10)	0.0145 (9)	0.0209 (10)	0.0008 (8)	0.0016 (8)	−0.0011 (8)
C1	0.0218 (11)	0.0178 (9)	0.0332 (12)	0.0000 (9)	0.0047 (9)	−0.0005 (9)
C2	0.0363 (13)	0.0221 (11)	0.0265 (11)	0.0009 (10)	0.0029 (10)	0.0007 (9)
C4	0.0348 (13)	0.0238 (10)	0.0282 (11)	−0.0002 (10)	0.0053 (10)	−0.0016 (9)
C3	0.0395 (14)	0.0205 (11)	0.0276 (12)	−0.0001 (10)	0.0033 (10)	−0.0028 (9)

O4—C5	1.245 (2)	N1—H1	0.8800
O3—C5	1.249 (2)	N1—C1	1.325 (3)
O1—H1A	0.8400	N1—C2	1.398 (2)
O1—C6	1.306 (2)	C5—C6	1.542 (3)
O6—H6A	0.8499	C1—C4	1.469 (3)
O6—H6B	0.8501	C2—H2A	0.9500
O2—C6	1.206 (2)	C2—C3	1.336 (3)
O5—H5A	0.8500	C4—H4A	0.9800
O5—H5B	0.8500	C4—H4B	0.9800
N2—H2	0.8800	C4—H4C	0.9800
N2—C1	1.323 (2)	C3—H3	0.9500
N2—C3	1.385 (2)
C6—O1—H1A	109.5	N2—C1—N1	107.91 (17)
H6A—O6—H6B	109.5	N2—C1—C4	126.36 (18)
H5A—O5—H5B	109.5	N1—C1—C4	125.72 (18)
C1—N2—H2	125.2	N1—C2—H2A	126.6
C1—N2—C3	109.64 (16)	C3—C2—N1	106.85 (18)
C3—N2—H2	125.2	C3—C2—H2A	126.6
C1—N1—H1	125.6	C1—C4—H4A	109.5
C1—N1—C2	108.83 (16)	C1—C4—H4B	109.5
C2—N1—H1	125.6	C1—C4—H4C	109.5
O4—C5—O3	127.68 (17)	H4A—C4—H4B	109.5
O4—C5—C6	115.41 (16)	H4A—C4—H4C	109.5
O3—C5—C6	116.90 (17)	H4B—C4—H4C	109.5
O1—C6—C5	113.79 (16)	N2—C3—H3	126.6
O2—C6—O1	124.38 (17)	C2—C3—N2	106.76 (18)
O2—C6—C5	121.81 (18)	C2—C3—H3	126.6
O4—C5—C6—O1	−173.95 (17)	C1—N1—C2—C3	0.0 (2)
O4—C5—C6—O2	7.3 (3)	C2—N1—C1—N2	0.0 (2)
O3—C5—C6—O1	6.9 (3)	C2—N1—C1—C4	179.0 (2)
O3—C5—C6—O2	−171.78 (19)	C3—N2—C1—N1	0.0 (2)
N1—C2—C3—N2	0.0 (2)	C3—N2—C1—C4	−179.1 (2)
C1—N2—C3—C2	0.0 (2)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O3	0.88	1.94	2.811 (2)	172
N1—H1···O1	0.88	2.50	2.991 (2)	116
N2—H2···O4i	0.88	1.97	2.842 (2)	169
N2—H2···O2i	0.88	2.49	2.977 (2)	116
O1—H1A···O5	0.84	1.69	2.5234 (19)	169
O6—H6A···O2ii	0.85	2.02	2.7893 (19)	150
O6—H6B···O3iii	0.85	1.87	2.700 (2)	166
O5—H5A···O6	0.85	1.82	2.672 (2)	176
O5—H5B···O4iv	0.85	1.88	2.720 (2)	167