Bis(imidazolium) galacta­rate dihydrate

In the structure of the title salt, 2C₃H₅N₂⁺·C₆H₈O₈²⁻·2H₂O, the galacta­rate dianions have crystallographic inversion symmetry and together with the water mol­ecules of solvation form hydrogen-bonded sheet substructures which extend along (110). The imidazolium cations link these sheets peripherally down c through carboxyl­ate O—H—N and N′—H...O_hy­droxy bridges, giving a three-dimensional framework structure.

Key indicators

• Single-crystal X-ray study
• T = 200 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.030
• wR factor = 0.082
• Data-to-parameter ratio = 11.7

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          3
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          4
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          2
PLAT042_ALERT_1_C Calc. and Reported MoietyFormula Strings  Differ          ?

Alert level G
PLAT793_ALERT_4_G The Model has Chirality at C2      (Verify) ....          R
PLAT793_ALERT_4_G The Model has Chirality at C3      (Verify) ....          S

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 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

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S1. Comment

Galactaric acid (mucic acid) (O'Neil, 2001) is the C6 homologue of tartaric acid but differs from it in being achiral and as well has only a small number of representative crystal structures in the CSD, e.g. the acid itself (Jeffrey & Wood, 1982), ammonium hydrogen galactarate (Bontchev & Moore, 2005), diammonium galactarate (Benetollo et al., 1993) and some metal complexes, e.g. copper(II) galactarate dihydrate (a fungicide) (Ferrier et al., 1998). Because the imidazolium cation has proved to be an excellent linking molecule for the generation of supramolecular layered structures particularly with dicarboxylic acids, including hydroxy acids (James & Matsushima, 1976; MacDonald et al., 2001; Aakeröy & Hitchcock, 1993; Fuller et al., 1995; Fukunaga & Ishida, 2003; Trivedi et al., 2003), we carried out a 1:2 stoichiometric reaction of galactaric acid with imidazole in aqueous ethanol and obtained large relatively hard, chemically stable crystals of the title compound, 2(CH₆N₃⁺) C₆H₈O₈^2-. 2H₂O (I), and the structure is reported here.

In the structure of (I) (Fig. 1), the galactarate anions lie across crystallographic inversion centres which is also the case in the structure of the parent acid (Jeffrey & Wood, 1982). Hydrogen-bonded anion-water sheets extending across the <100> planes in the unit cell (Fig. 2) are formed through hydroxyl O31–H···O12ⁱⁱⁱ_carboxyl and water-bridging O31···O11^iv_carboxyl interactions (for symmetry codes, see Table 1). These include R²₂(12) and R³₃(12) cyclic motifs (Etter et al., 1990). The layered substructures are linked peripherally down the c cell direction by the imidazolium cations through carboxyl O···H—N,N'—H···O`_hydroxyl bridges giving a three-dimensional framework structure (Fig. 3). The structure of (I) differs from those of the anhydrous 1:1 salts of the hydrogen dicarboxylates (MacDonald et al., 2001) in which the bridging imidazolium cations are incorporated within two-dimensional layered structures.

Related literature

For mention of mucic acid in the Merck Index, see: O'Neil (2001). For the structures of imidazolium hydrogen salts of aliphatic dicarboxylic acids, see: James & Matsushima (1976); MacDonald et al. (2001); Aakeröy & Hitchcock (1993); Fuller et al. (1995); Fukunaga & Ishida (2003); Trivedi et al. (2003). For the structures of galactaric acid, ammonium H galactarate, diammonium galactarate and copper(II) galactarate dihydrate, see: Jeffrey & Wood (1982), Bontchev & Moore (2005), Benetollo et al. (1993) and Ferrier et al. (1998) respectively. For graph-set analysis, see: Etter et al. (1990).

S2. Experimental

The title compound was synthesized by heating together under reflux for 10 minutes 1 mmol of galactaric acid (mucic acid) and 2 mmol of imidazole in 50 ml of 50% ethanol-water. After concentration to ca 30 ml, partial room temperature evaporation of the hot-filtered solution gave large colourless plates of (I) (m.p. 435 K) from which a suitable analytical specimen was cleaved.

S3. Refinement

Hydrogen atoms potentially involved in hydrogen-bonding interactions were located by difference methods and their positional and isotropic displacement parameters were refined. Other H atoms were included in the refinement in calculated positions (C–H_aromatic = 0.95 Å and others = 1.00 Å) and allowed to ride, with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: CrysAlis PRO (Oxford Diffraction, 2010); cell refinement: CrysAlis PRO (Oxford Diffraction, 2010); data reduction: CrysAlis PRO (Oxford Diffraction, 2010); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) within WinGX (Farrugia, 1999); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular configuration and atom-numbering scheme for the cation, dianion and water species in (I). The galactarate dianion has inversion symmetry [symmetry code: (i) -x + 1, -y + 1, -z + 2]. Non-H atoms are shown as 50% probability ellipsoids and inter-species hydrogen bonds are shown as dashed lines.
	Fig. 2. Hydrogen-bonded anion-water sheet substructures in (I), extending across (110) (imidazolium cations are omitted). For symmetry codes, see Table 1. Hydrogen bonds are shown as dashed lines.
	Fig. 3. The three-dimensional structure of (I) viewed down the approximate a cell direction, showing the imidazolium bridges.

Bis(imidazolium) galactarate dihydrate

Crystal data

2C3H5N2^+·C6H8O8^2^−·2H2O	Z = 1
Mr = 382.34	F(000) = 202
Triclinic, P1	Dx = 1.494 Mg m^−3
Hall symbol: -P 1	Melting point: 435 K
a = 6.9184 (4) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.1336 (4) Å	Cell parameters from 3387 reflections
c = 9.3652 (5) Å	θ = 3.5–28.7°
α = 92.000 (5)°	µ = 0.13 mm^−1
β = 100.559 (5)°	T = 200 K
γ = 109.835 (6)°	Plate, colourless
V = 425.06 (5) Å^3	0.45 × 0.45 × 0.30 mm

Data collection

Oxford Diffraction Gemini-S CCD-detector diffractometer	1657 independent reflections
Radiation source: Enhance (Mo) X-ray source	1431 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
ω scans	θmax = 26.0°, θmin = 3.5°
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2010)	h = −8→8
Tmin = 0.965, Tmax = 0.980	k = −8→8
4949 measured reflections	l = −11→11

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.082	H atoms treated by a mixture of independent and constrained refinement
S = 1.13	w = 1/[σ^2(Fo^2) + (0.0444P)^2 + 0.0516P] where P = (Fo^2 + 2Fc^2)/3
1657 reflections	(Δ/σ)max = 0.001
142 parameters	Δρmax = 0.30 e Å^−3
0 restraints	Δρmin = −0.20 e Å^−3

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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
O11	0.18384 (15)	−0.07229 (13)	0.80626 (9)	0.0234 (3)
O12	0.26773 (14)	−0.02982 (13)	1.04961 (9)	0.0207 (3)
O21	0.19607 (14)	0.29951 (14)	0.78260 (9)	0.0203 (3)
O31	0.62559 (14)	0.35914 (13)	0.90945 (10)	0.0197 (3)
C1	0.23436 (18)	0.03283 (17)	0.92558 (13)	0.0154 (3)
C2	0.25848 (18)	0.25478 (17)	0.92684 (12)	0.0151 (3)
C3	0.48566 (18)	0.38863 (17)	0.99549 (13)	0.0153 (3)
N11	0.34766 (19)	0.22454 (18)	0.54570 (12)	0.0261 (4)
N31	0.35478 (19)	0.13600 (18)	0.32587 (12)	0.0265 (4)
C21	0.2302 (2)	0.1404 (2)	0.41585 (14)	0.0269 (4)
C41	0.5588 (2)	0.2202 (2)	0.40018 (15)	0.0302 (5)
C51	0.5544 (2)	0.2764 (2)	0.53780 (15)	0.0285 (4)
O1W	−0.02769 (16)	0.53271 (15)	0.78655 (11)	0.0244 (3)
H22	0.118 (3)	0.373 (3)	0.7852 (19)	0.046 (5)*
H2	0.16380	0.28050	0.98780	0.0180*
H3	0.52450	0.35200	1.09610	0.0180*
H32	0.657 (3)	0.260 (3)	0.9315 (18)	0.040 (5)*
H11	0.301 (3)	0.245 (3)	0.625 (2)	0.048 (5)*
H21	0.08100	0.09150	0.39160	0.0320*
H31	0.318 (3)	0.084 (3)	0.233 (2)	0.044 (5)*
H41	0.68070	0.23610	0.36180	0.0360*
H51	0.67240	0.34010	0.61480	0.0340*
H11W	0.043 (3)	0.660 (4)	0.803 (2)	0.057 (6)*
H12W	−0.127 (4)	0.500 (3)	0.835 (2)	0.059 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O11	0.0320 (5)	0.0168 (5)	0.0185 (5)	0.0058 (4)	0.0047 (4)	−0.0032 (4)
O12	0.0290 (5)	0.0158 (5)	0.0174 (4)	0.0077 (4)	0.0056 (4)	0.0024 (3)
O21	0.0257 (5)	0.0230 (5)	0.0157 (5)	0.0135 (4)	0.0032 (4)	0.0023 (4)
O31	0.0214 (5)	0.0149 (5)	0.0265 (5)	0.0079 (4)	0.0113 (4)	0.0032 (4)
C1	0.0129 (6)	0.0148 (6)	0.0174 (6)	0.0026 (5)	0.0051 (4)	0.0001 (5)
C2	0.0185 (6)	0.0143 (6)	0.0132 (6)	0.0058 (5)	0.0049 (5)	0.0009 (5)
C3	0.0185 (6)	0.0136 (6)	0.0144 (6)	0.0052 (5)	0.0054 (5)	0.0017 (5)
N11	0.0347 (7)	0.0308 (7)	0.0175 (6)	0.0160 (5)	0.0084 (5)	0.0031 (5)
N31	0.0379 (7)	0.0260 (6)	0.0152 (6)	0.0116 (5)	0.0044 (5)	0.0010 (5)
C21	0.0273 (7)	0.0304 (8)	0.0230 (7)	0.0104 (6)	0.0043 (6)	0.0070 (6)
C41	0.0311 (8)	0.0336 (8)	0.0301 (8)	0.0134 (6)	0.0120 (6)	0.0064 (6)
C51	0.0286 (7)	0.0294 (8)	0.0241 (7)	0.0085 (6)	0.0007 (6)	0.0004 (6)
O1W	0.0231 (5)	0.0180 (5)	0.0325 (6)	0.0063 (4)	0.0095 (4)	−0.0005 (4)

Geometric parameters (Å, º)

O11—C1	1.2465 (15)	N11—H11	0.89 (2)
O12—C1	1.2690 (15)	N31—H31	0.890 (18)
O21—C2	1.4223 (14)	C1—C2	1.5341 (16)
O31—C3	1.4293 (16)	C2—C3	1.5375 (18)
O21—H22	0.87 (2)	C3—C3^i	1.5303 (16)
O31—H32	0.83 (2)	C2—H2	1.0000
O1W—H11W	0.87 (3)	C3—H3	1.0000
O1W—H12W	0.86 (3)	C41—C51	1.345 (2)
N11—C21	1.3249 (17)	C21—H21	0.9500
N11—C51	1.367 (2)	C41—H41	0.9500
N31—C21	1.3178 (19)	C51—H51	0.9500
N31—C41	1.369 (2)
C2—O21—H22	108.6 (11)	O31—C3—C3^i	107.52 (10)
C3—O31—H32	110.6 (13)	O21—C2—H2	108.00
H11W—O1W—H12W	111 (2)	C3—C2—H2	108.00
C21—N11—C51	108.65 (12)	C1—C2—H2	108.00
C21—N31—C41	108.66 (11)	O31—C3—H3	109.00
C51—N11—H11	125.3 (14)	C2—C3—H3	109.00
C21—N11—H11	126.1 (14)	C3^i—C3—H3	109.00
C41—N31—H31	123.6 (14)	N11—C21—N31	108.63 (13)
C21—N31—H31	127.7 (14)	N31—C41—C51	107.15 (13)
O12—C1—C2	116.02 (10)	N11—C51—C41	106.92 (12)
O11—C1—O12	124.82 (11)	N31—C21—H21	126.00
O11—C1—C2	119.16 (10)	N11—C21—H21	126.00
O21—C2—C3	111.32 (10)	N31—C41—H41	126.00
O21—C2—C1	110.05 (9)	C51—C41—H41	126.00
C1—C2—C3	110.45 (10)	N11—C51—H51	127.00
O31—C3—C2	109.98 (9)	C41—C51—H51	127.00
C2—C3—C3^i	112.11 (10)
C21—N11—C51—C41	−0.42 (16)	C1—C2—C3—C3^i	−177.68 (10)
C51—N11—C21—N31	0.31 (16)	C1—C2—C3—O31	62.76 (12)
C21—N31—C41—C51	−0.19 (16)	O21—C2—C3—C3^i	59.76 (13)
C41—N31—C21—N11	−0.08 (16)	O31—C3—C3^i—O31^i	179.98 (12)
O11—C1—C2—O21	5.67 (17)	C2—C3—C3^i—O31^i	59.01 (12)
O12—C1—C2—O21	−174.06 (11)	C2—C3—C3^i—C2^i	−179.98 (12)
O12—C1—C2—C3	62.63 (14)	O31—C3—C3^i—C2^i	−59.01 (12)
O11—C1—C2—C3	−117.63 (13)	N31—C41—C51—N11	0.36 (16)
O21—C2—C3—O31	−59.81 (13)

Symmetry code: (i) −x+1, −y+1, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N11—H11···O21	0.89 (2)	1.84 (2)	2.7311 (15)	175.9 (19)
N31—H31···O12^ii	0.890 (18)	1.795 (19)	2.6810 (14)	174 (2)
O21—H22···O1W	0.87 (2)	1.76 (2)	2.6324 (15)	177 (2)
O31—H32···O12^iii	0.83 (2)	1.89 (2)	2.7104 (13)	170.9 (16)
O1W—H11W···O11^iv	0.87 (3)	1.82 (3)	2.6799 (14)	170.9 (18)
O1W—H12W···O31^v	0.86 (3)	1.94 (3)	2.7763 (15)	164.4 (19)
C21—H21···O11^vi	0.95	2.32	3.0935 (17)	138
C41—H41···O11^vii	0.95	2.42	3.2273 (18)	142
C51—H51···O1W^viii	0.95	2.34	3.2827 (18)	173

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