2-Ethyl-1H-imidazol-3-ium hemioxalate oxalic acid monohydrate

In the title compound, C₅H₉N₂⁺·0.5C₂O₄²⁻·C₂H₂O₄·H₂O, the anions, cations and water mol­eculars are linked by N—H...O and O—H...O hydrogen bonds which define a tightly bound three-dimensional structure. The title compound is a layered structure as viewed along the a or c axis; one layer contains water and oxalic acid mol­ecules, the other the imidazolium cation. The C atoms of the ethyl group of the 2-ethyl­imidazolium cation are disordered over two positions of equal occupancy.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• Disorder in main residue
• R factor = 0.046
• wR factor = 0.115
• Data-to-parameter ratio = 14.3

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT042_ALERT_1_C Calc. and Reported MoietyFormula Strings  Differ          ?
PLAT045_ALERT_1_C Calculated and Reported Z Differ by ............       2.00 Ratio
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.51
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.65
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          2
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          6
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          2

Alert level G
PLAT003_ALERT_2_G Number of Uiso or Uij Restrained Atom Sites ....          4
PLAT194_ALERT_1_G Missing _cell_measurement_reflns_used datum ....          ?
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT242_ALERT_2_G Check Low       Ueq as Compared to Neighbors for         C4
PLAT242_ALERT_2_G Check Low       Ueq as Compared to Neighbors for        C4'
PLAT301_ALERT_3_G Note: Main Residue  Disorder ...................         10 Perc.
PLAT432_ALERT_2_G Short Inter X...Y Contact  C6     ..  C6      ..       3.15 Ang.
PLAT720_ALERT_4_G Number of Unusual/Non-Standard Labels ..........          5
PLAT779_ALERT_4_G Suspect or Irrelevant (Bond) Angle in CIF .... #         12
              C4'  -C3   -C4      1.555   1.555   1.555             35.90 Deg.
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          3

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   7 ALERT level C = Check. Ensure it is not caused by an omission or oversight
  11 ALERT level G = General information/check it is not something unexpected

   5 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   6 ALERT type 2 Indicator that the structure model may be wrong or deficient
   5 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

S1. Comment

The basic method to find potential ferroelectric phase change material is Dielectric constant measurement of compounds with temperature (Fu et al., 2009; Ye et al., 2006; Zhang et al., 2008; Zhang et al., 2010). Unfortunately, the title compound's dielectric dose not appear strange from 80 K to 298 K (m.p.219–229).

By X-ray diffraction analysis in 123 K, we can define the structure of title compound as Fig.1. Title compound, of the formula [C₅H₉N₂] ₂⁺ [C₂O₄]^2-.C₂H₂O₄.2H₂O, was obtained by 2 - ethyl imidazole, oxalic acid in water in basic aqueous solution and was isolated as colourless crystals. The whole molecules are organized in a three-dimensional structure involving hydrogen bonds, both intercationic and between cations and water molecules. The O···O distances of the hydrogen bonding are observed to be in the range of 2.476 (3)–2.924 (3) Å and the N···O distances of the hydrogen bonding are in the range of 2.054 (2) - 3.059 (2) Å for table1.

Related literature

For general background on ferroelectric organic frameworks, see: Fu et al. (2009); Ye et al. (2006); Zhang et al. (2008, 2010).

S2. Experimental

A mixture of 2 - ethyl imidazole (2.4 g, 25 mmol), oxalic acid (3.15 g, 25 mmol) in water was stirred for several days at ambient temperature, Colourless sheet crystals were obtained.

S3. Refinement

Positional parameter of all the H atoms except for H7A and H7B were calculated geometrically and the H atoms were set to ride on the C atoms to which they are bonded, with U_iso(H) =1.2Ueq(C). The H7A and H7B on the O7 was freely refined.

Computing details

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); 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: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. A partial packing diagram of the title compound, with the displacement ellipsoids were drawn at the 30% probability level.
	Fig. 2. Packing diagram of the title compound, hydrogen bonds are shown as dashed lines.

2-Ethyl-1H-imidazol-3-ium hemioxalate oxalic acid monohydrate

Crystal data

C5H9N2^+·0.5C2O4^2^−·C2H2O4·H2O	Z = 4
Mr = 249.20	F(000) = 524.0
Monoclinic, P21/c	Dx = 1.444 Mg m^−3
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 6.971 (3) Å	θ = 2.3–27.5°
b = 15.716 (7) Å	µ = 0.13 mm^−1
c = 10.484 (4) Å	T = 293 K
β = 93.736 (8)°	Prism, colourless
V = 1146.1 (8) Å^3	0.30 × 0.25 × 0.20 mm

Data collection

Rigaku SCXmini diffractometer	2614 independent reflections
Radiation source: fine-focus sealed tube	2192 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
CCD_Profile_fitting scans	θmax = 27.5°, θmin = 2.9°
Absorption correction: multi-scan (CrystalClear; Rigaku, 2005)	h = −9→9
Tmin = 0.962, Tmax = 0.975	k = −20→20
12371 measured reflections	l = −13→13

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)] = 0.046	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.115	w = 1/[σ^2(Fo^2) + (0.0549P)^2 + 0.3631P] where P = (Fo^2 + 2Fc^2)/3
S = 1.08	(Δ/σ)max < 0.001
2614 reflections	Δρmax = 0.35 e Å^−3
183 parameters	Δρmin = −0.44 e Å^−3
3 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008)
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0

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	Occ. (<1)
C1	0.1308 (3)	0.28168 (12)	0.2483 (2)	0.0343 (4)
H1	0.0466	0.3066	0.3025	0.041*
C2	0.1140 (3)	0.20420 (12)	0.1945 (2)	0.0364 (5)
H2	0.0158	0.1652	0.2044	0.044*
C3	0.3798 (4)	0.26258 (12)	0.1326 (2)	0.0475 (6)
C6	0.2852 (2)	0.51305 (9)	0.44765 (14)	0.0159 (3)
C7	0.1981 (2)	0.55010 (10)	0.56719 (14)	0.0181 (3)
C8	0.9398 (2)	0.49850 (10)	0.06011 (14)	0.0169 (3)
N1	0.2691 (3)	0.19373 (9)	0.12234 (15)	0.0358 (4)
H1B	0.2914	0.1495	0.0774	0.043*
N2	0.2952 (2)	0.31678 (9)	0.20807 (16)	0.0349 (4)
H2A	0.3378	0.3666	0.2286	0.042*
O1	0.14141 (16)	0.48966 (7)	0.64012 (10)	0.0203 (3)
H1A	0.0967	0.5104	0.7036	0.031*
O2	0.1875 (2)	0.62570 (8)	0.58419 (13)	0.0393 (4)
O3	0.31598 (17)	0.43711 (7)	0.43807 (10)	0.0212 (3)
O4	0.32172 (16)	0.57027 (7)	0.36275 (10)	0.0201 (3)
H4	0.3622	0.5469	0.2999	0.030*
O5	0.76442 (16)	0.51317 (9)	0.04421 (11)	0.0278 (3)
O6	1.03061 (15)	0.48204 (8)	0.16451 (10)	0.0218 (3)
O7	0.54960 (17)	0.51036 (7)	0.82209 (11)	0.0202 (3)
H7A	0.442 (4)	0.5011 (14)	0.852 (2)	0.042 (6)*
H7B	0.631 (4)	0.5075 (15)	0.890 (3)	0.054 (7)*
C4	0.5878 (6)	0.2787 (2)	0.0900 (3)	0.0317 (8)	0.655 (6)
H4A	0.6477	0.3251	0.1390	0.038*	0.655 (6)
H4B	0.6659	0.2281	0.1040	0.038*	0.655 (6)
C5	0.5713 (5)	0.3010 (2)	−0.0500 (3)	0.0474 (11)	0.655 (6)
H5A	0.6971	0.3114	−0.0788	0.071*	0.655 (6)
H5B	0.4938	0.3511	−0.0627	0.071*	0.655 (6)
H5C	0.5126	0.2546	−0.0976	0.071*	0.655 (6)
C5'	0.6915 (11)	0.2936 (4)	0.0908 (7)	0.0416 (18)	0.345 (6)
H5'A	0.7855	0.3046	0.0299	0.062*	0.345 (6)
H5'B	0.7294	0.2445	0.1408	0.062*	0.345 (6)
H5'C	0.6822	0.3419	0.1459	0.062*	0.345 (6)
C4'	0.4958 (9)	0.2770 (3)	0.0199 (6)	0.0285 (17)	0.345 (6)
H4'A	0.4507	0.3258	−0.0301	0.034*	0.345 (6)
H4'B	0.4980	0.2272	−0.0347	0.034*	0.345 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0365 (10)	0.0252 (9)	0.0430 (11)	0.0018 (7)	0.0161 (9)	−0.0093 (8)
C2	0.0340 (10)	0.0249 (9)	0.0510 (12)	0.0005 (8)	0.0089 (9)	−0.0090 (9)
C3	0.0680 (14)	0.0176 (8)	0.0619 (14)	0.0043 (8)	0.0436 (12)	−0.0004 (9)
C6	0.0147 (7)	0.0181 (7)	0.0152 (7)	−0.0011 (5)	0.0025 (5)	0.0011 (6)
C7	0.0186 (7)	0.0197 (8)	0.0167 (7)	0.0002 (6)	0.0054 (6)	−0.0007 (6)
C8	0.0158 (7)	0.0207 (7)	0.0148 (7)	0.0004 (6)	0.0047 (6)	−0.0005 (6)
N1	0.0606 (11)	0.0176 (7)	0.0312 (8)	0.0073 (6)	0.0169 (8)	−0.0054 (6)
N2	0.0422 (9)	0.0179 (7)	0.0466 (10)	0.0011 (6)	0.0166 (8)	−0.0085 (7)
O1	0.0273 (6)	0.0199 (6)	0.0149 (5)	0.0002 (4)	0.0096 (4)	0.0004 (4)
O2	0.0628 (9)	0.0165 (6)	0.0427 (8)	0.0004 (6)	0.0359 (7)	−0.0034 (5)
O3	0.0300 (6)	0.0157 (5)	0.0188 (6)	0.0006 (4)	0.0085 (5)	0.0001 (4)
O4	0.0275 (6)	0.0173 (5)	0.0166 (5)	0.0009 (4)	0.0089 (4)	0.0024 (4)
O5	0.0141 (6)	0.0540 (8)	0.0158 (6)	0.0034 (5)	0.0051 (4)	0.0023 (5)
O6	0.0172 (6)	0.0350 (7)	0.0134 (5)	0.0028 (5)	0.0037 (4)	0.0025 (5)
O7	0.0159 (6)	0.0284 (6)	0.0168 (6)	0.0005 (5)	0.0046 (5)	−0.0002 (5)
C4	0.0362 (17)	0.0220 (15)	0.0368 (16)	0.0076 (14)	0.0020 (19)	−0.0043 (12)
C5	0.051 (2)	0.048 (2)	0.0449 (17)	0.0109 (16)	0.0211 (17)	0.0148 (16)
C5'	0.028 (4)	0.037 (4)	0.059 (4)	−0.001 (3)	−0.001 (3)	−0.014 (3)
C4'	0.036 (3)	0.023 (3)	0.028 (4)	0.002 (2)	0.010 (3)	−0.002 (2)

Geometric parameters (Å, º)

C1—C2	1.344 (3)	N2—H2A	0.8600
C1—N2	1.363 (3)	O1—H1A	0.8200
C1—H1	0.9300	O4—H4	0.8200
C2—N1	1.369 (2)	O7—H7A	0.84 (3)
C2—H2	0.9300	O7—H7B	0.88 (3)
C3—N1	1.329 (3)	C4—C5	1.505 (5)
C3—N2	1.327 (2)	C4—H4A	0.9700
C3—C4'	1.491 (6)	C4—H4B	0.9700
C3—C4	1.565 (5)	C5—H5A	0.9600
C6—O3	1.2179 (19)	C5—H5B	0.9600
C6—O4	1.3022 (18)	C5—H5C	0.9600
C6—C7	1.542 (2)	C5'—C4'	1.532 (10)
C7—O2	1.204 (2)	C5'—H5'A	0.9600
C7—O1	1.2970 (19)	C5'—H5'B	0.9600
C8—O5	1.2449 (19)	C5'—H5'C	0.9600
C8—O6	1.2550 (19)	C4'—H4'A	0.9700
C8—C8^i	1.559 (3)	C4'—H4'B	0.9700
N1—H1B	0.8600
C2—C1—N2	106.81 (16)	C7—O1—H1A	109.5
C2—C1—H1	126.6	C6—O4—H4	109.5
N2—C1—H1	126.6	H7A—O7—H7B	104 (2)
C1—C2—N1	106.87 (17)	C5—C4—C3	107.6 (3)
C1—C2—H2	126.6	C5—C4—H4A	110.2
N1—C2—H2	126.6	C3—C4—H4A	110.2
N1—C3—N2	106.99 (18)	C5—C4—H4B	110.2
N1—C3—C4'	113.7 (3)	C3—C4—H4B	110.2
N2—C3—C4'	131.3 (3)	H4A—C4—H4B	108.5
N1—C3—C4	130.74 (19)	C4—C5—H5A	109.5
N2—C3—C4	121.5 (2)	C4—C5—H5B	109.5
C4'—C3—C4	35.9 (3)	H5A—C5—H5B	109.5
O3—C6—O4	125.24 (14)	C4—C5—H5C	109.5
O3—C6—C7	121.20 (13)	H5A—C5—H5C	109.5
O4—C6—C7	113.55 (13)	H5B—C5—H5C	109.5
O2—C7—O1	127.68 (14)	C4'—C5'—H5'A	109.5
O2—C7—C6	121.60 (14)	C4'—C5'—H5'B	109.5
O1—C7—C6	110.71 (13)	H5'A—C5'—H5'B	109.5
O5—C8—O6	126.16 (14)	C4'—C5'—H5'C	109.5
O5—C8—C8^i	117.49 (17)	H5'A—C5'—H5'C	109.5
O6—C8—C8^i	116.35 (16)	H5'B—C5'—H5'C	109.5
C3—N1—C2	109.44 (15)	C3—C4'—C5'	98.8 (5)
C3—N1—H1B	125.3	C3—C4'—H4'A	112.0
C2—N1—H1B	125.3	C5'—C4'—H4'A	112.0
C3—N2—C1	109.87 (16)	C3—C4'—H4'B	112.0
C3—N2—H2A	125.1	C5'—C4'—H4'B	112.0
C1—N2—H2A	125.1	H4'A—C4'—H4'B	109.7

Symmetry code: (i) −x+2, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1B···O3^ii	0.86	2.01	2.855 (2)	166
N1—H1B···O1^ii	0.86	2.53	3.026 (2)	118
N2—H2A···O7^iii	0.86	2.17	2.949 (2)	151
N2—H2A···O3	0.86	2.47	3.060 (2)	126
O1—H1A···O6^iii	0.82	1.70	2.4800 (16)	159
O4—H4···O7^iii	0.82	1.71	2.5283 (17)	174
O7—H7A···O5^iii	0.84 (3)	1.87 (3)	2.7006 (18)	166 (2)
O7—H7B···O5^iv	0.88 (3)	1.82 (3)	2.6856 (19)	169 (2)
O7—H7B···O6^v	0.88 (3)	2.47 (3)	2.923 (2)	113 (2)

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