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The asymmetric unit of the title salt formed between 2,3,5,6-tetra­fluoro­terephthalic acid (H2tfbdc) and imidazolium (ImH), C3H5N2+·C8HF4O4-, contains one Htfbdc- anion and one ImH2+ cation, joined by a classical N-H...O hydrogen bond. The acid and base subunits are further linked by N-H...O and O-H...O hydrogen bonds into infinite two-dimensional layers with R56(32) hydrogen-bond motifs. The resulting (4,4) network layers interpenetrate to produce an inter­locked three-dimensional structure. The final three-dimensional supra­molecular architecture is further stabilized by the linkages of two C-H...O inter­actions.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270110004221/sq3234sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270110004221/sq3234Isup2.hkl
Contains datablock I

CCDC reference: 774899

Comment top

Hydrogen bonding has long been considered important in biological systems and molecular recognition (Philp & Stoddart, 1996). Nowadays, the application of intermolecular hydrogen bonds is a well known and efficient tool to design and synthesize supramolecular assemblies (Prior & Rosseinsky, 2000; Beatty, 2003; Bhogala et al., 2005). Classical hydrogen bonds (such as O—H···O, O—H···N etc.) have proven to be ideal tools to rationalize and systematize the relationship between molecular and supramolecular structures (Desiraju & Steiner, 1999; Steiner & Desiraju, 1998; Mascal et al., 2000). For example, many organic crystalline materials, composed of N-donor compounds such as ImH, benzimidazole, pyridine and 4,4'-bipyridinium, and aromatic multi-carboxylic acids such as 1,4-benzenedicarboxylic acid, 1,3,5-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid and 1,2,3,4,5,6-benzenehexacarboxylic acid, have been documented. Although coordination compounds synthesized with halogen-substituted aromatic multi-carboxylic acids have been reported (Wang et al., 2007; Roques et al., 2007; Liu et al., 2008; Sergio et al., 2008; Chen et al., 2008, 2006; Li et al., 2008; Eddaoudi et al., 2002), to the best of our knowledge studies of their supramolecular interactions have been less well explored (Luo & Palmore, 2002; Lan et al., 2008; He et al., 2009). Recently, we have obtained two complexes with 2,3,5,6-tetrafluoroterephthalic acid (H2tfbdc) under mild solution synthetic conditions (Zhu et al., 2008, 2009). To further the development of such interesting hydrogen-bonded supramolecular systems and as a continuation of our research in this area, we deliberately chose H2tfbdc to react with an excellent N-donor compound, imidazole (ImH), and isolated the the first organic crystalline product containing the Htfbdc- anion. The title salt, (I), was an unexpected product of an attempt to form an extended structure incorporating Cd2+ cations.

Compound (I) crystallizes in the orthorhombic space group Pna21. The asymmetric unit contains one Htfbdc- anion and one ImH2+ cation, linked by an N—H···O hydrogen bond between the protonated amine and the deprotonated carboxylate group (Fig. 1). Proton transfer from the H2tfbdc to the ImH was unequivocally established from difference map plots. The compound is thus shown to be an organic proton-transfer binary salt, in which the acidic H+ of one carboxyl group O atom is transferred to an imidazole N atom, while the other carboxyl group remains as the acid. The carboxylic acid and carboxylate groups are distinctly twisted away from the arene ring, with dihedral angles of 49.1 (1) and 51.5 (1)°, respectively, notably larger than the corresponding values in 4-methylimidazolium hydrogenterephthalate [5.7 (1) and 21.9 (1)°, respectively; Meng et al., 2008]. The plane of the aromatic ring of the Htfbdc- anion is inclined at 40.9 (1)° to that of the ImH2+ component, which is much smaller than the analogous angle in 4-methylimidazolium hydrogenterephthalate [60.6 (1)°; Meng et al., 2008]. These differences may be due to the influence of the steric hindrance of the adjacent fluoro substituents.

The carboxyl/carboxylate C—O bond lengths in (I) [C7—O1 = 1.233 (3), C7—O2 = 1.260 (2), C8—O3 = 1.307 (3) and C8—O4 = 1.201 (3) Å] agree well with those tabulated by Allen et al. (1995) for a carboxyl [1.305 (20) and 1.226 (20) Å] and/or a carboxylate group [1.255 (10) Å] attached to an arene ring. The bond distances and angles in the ImH2+ cation are also indicative of its protonation compared with analogous compounds.

In the extended structure of (I) (Fig. 2), linear tapes of Htfbdc- anions are generated along the a axis through O3—H3···O2ii hydrogen bonds [symmetry code: (ii) x + 1, y, z] (Table 1). The distance between the two carboxyl O atoms in the hydrogen bond is slightly shorter than those seen in other carboxylic acid compounds, such as terephthalic acid (2.620 Å; Domenicano et al., 1990) and bis(2,4'-bipyridin-1'-ium)2,5-dicarboxybenzene-1,4-carboxylate benzene-1,2,4,5-tetracarboxylic acid (2.607 Å; Cui et al., 2005), indicating the strength of the interactions in (I). The linear tapes are very similar to the one-dimensional chains formed by the hydrogenterephthalate anions in 4-methylimidazolium hydrogenterephthalate (Meng et al., 2008).

Adjacent anion chains are linked together by ImH2+ cations via N1—H1A···O2 and N2—H2A···O1i hydrogen bonds [symmetry code: (i) -x + 1/2, y + 1/2, z + 1/2], forming two-dimensional layers containing R56(32) hydrogen-bond motifs (Fig. 2) (for definition of graph-set notation, see Bernstein et al., 1995). The network thus formed is topologically equivalent to a (4,4) network (Batten & Robson, 1998). Each cavity is interwoven by another network in the so-called alternative [Alternating?] mode of inclined interpenetration, with an angle of interpenetration of 45.1° (Fig. 3), producing an interlocked three-dimensional structure.

The ImH2+ cations linked to opposite sides of the same Htfbdc- anion chain are almost perpendicular to each other [82.0 (1)°], while the dihedral angle between the Htfbdc- rings of different chains is 23.5 (1)°. This pattern is somewhat different from what is seen in the two-dimensional layers formed by similar strong O—H···O and N—H···O hydrogen bonds with an R46(32) ring pattern in 4-methylimidazolium hydrogenterephthalate (Meng et al., 2008), in which the Htfbdc- anions of adjacent chains are parallel to each other and all 4-methylimidazolium cations are oriented in the same direction, so that the resulting (4,4) network layers are also parallel to each other.

Compound (I) extends further to its final three-dimensional network through weak intermolecular C9—H9A···O4iii and C11—H11A···O1iv interactions (Table 1) [symmetry codes: (iii) x - 1/2, -y + 3/2, z; (iv) -x, -y + 1, z + 1/2]. The H···A lengths of these hydrogen bonds are in the range 2.30–2.60 Å, comparable with those found in protein complexes (Jiang & Lai, 2002).

This work demonstrates the first example of a fluorinated terephthalic acid as a good participant in organic salt formation with an N-donor compound. Compound (I) is linked by O—H···O and N—H···O hydrogen bonds into an interlocked three-dimensional structure in an alternative [Alternating?] mode of inclined interpenetration of (4,4) network layers. Additional studies are warranted to provide further insight into the potential of these molecules to form engineered structures in salts or co-crystals.

Experimental top

All reagents and solvents employed were commercially available and used as supplied without further purification. For the preparation of (I), solid Cd(OH)2 (0.0365 g, 0.25 mmol), which is necessary for the crystallization of the product, was added to an ethanol–water (1:1 v/v) solution (5 ml) of H2tfbdc (0.0595 g, 0.25 mmol) and ImH (0.0170 g, 0.25 mmol). After stirring for 1 h, the reaction mixture was filtered and left to stand at ambient temperature. Colourless block-shaped crystals of (I), suitable for X-ray diffraction, were obtained after evaporation of the filtrate for one week [yield 67%, 0.0513 g (based on ImH)]. Analysis, calculated for C11H6F4N2O4: C 43.15, H 1.98, N 9.15%; found: C 43.17, H 1.20, N 9.13%. Spectroscopic analysis: IR (KBr pellet, ν, cm-1): 3169 (s), 2992 (w), 2856 (w), 1721 (w), 1626 (m), 1590 (m), 1474 (s), 1366 (m), 1307 (s), 1213 (m), 1178 (w), 1055 (m), 991 (s), 768 (m), 707(s), 631 (m), 508 (m), 488 (s).

Refinement top

All C-bound H atoms were positioned theoretically and treated as riding atoms, with C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C). N- and O-bound H atoms were initially located in difference maps, then geometrically optimized and refined as riding, with N—H = 0.86 Å and O—H = 0.82 Å, and with Uiso(H) = 1.2Ueq(N) or 1.5Ueq(O). Friedel pairs were collected but merged before the final refinement and the absolute configuration was chosen arbitrarily.

Computing details top

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. The hydrogen bond is shown as a dashed line.
[Figure 2] Fig. 2. Part of the crystal structure of (I), showing the formation of the two-dimensional layer network with (4,4) topology running parallel to the (024) plane. Hydrogen bonds are shown as dashed lines. [Symmetry codes: (i) -x + 1/2, y + 1/2, z + 1/2; (ii) x + 1, y, z.]
[Figure 3] Fig. 3. A view of the alternative [Alternating?] mode of inclined interpenetration of (4,4) networks in the structure of (I). Four such networks are shown. Hydrogen bonds are shown as dashed lines. For the sake of clarity, H atoms not involved in the motif and all F atoms have been omitted.
Imidazolium hydrogen 2,3,5,6-tetrafluoroterephthalate top
Crystal data top
C3H5N2+·C8F4HO4F(000) = 616
Mr = 306.18Dx = 1.664 Mg m3
Orthorhombic, Pna21Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2nCell parameters from 3571 reflections
a = 9.716 (3) Åθ = 2.3–27.6°
b = 7.229 (3) ŵ = 0.17 mm1
c = 17.406 (6) ÅT = 296 K
V = 1222.5 (7) Å3Block, colourless
Z = 40.30 × 0.30 × 0.20 mm
Data collection top
Bruker SMART APEX CCD
diffractometer
1457 independent reflections
Radiation source: fine-focus sealed tube1330 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.029
Detector resolution: 0 pixels mm-1θmax = 27.6°, θmin = 2.3°
ϕ and ω scansh = 1212
Absorption correction: multi-scan
(SADABS; Bruker, 2000)
k = 99
Tmin = 0.952, Tmax = 0.968l = 2222
9957 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.027H-atom parameters constrained
wR(F2) = 0.074 w = 1/[σ2(Fo2) + (0.0451P)2 + 0.0992P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max < 0.001
1457 reflectionsΔρmax = 0.25 e Å3
191 parametersΔρmin = 0.16 e Å3
1 restraintExtinction correction: SHELXL97 (Sheldrick, 2008), Fc* = kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.018 (2)
Crystal data top
C3H5N2+·C8F4HO4V = 1222.5 (7) Å3
Mr = 306.18Z = 4
Orthorhombic, Pna21Mo Kα radiation
a = 9.716 (3) ŵ = 0.17 mm1
b = 7.229 (3) ÅT = 296 K
c = 17.406 (6) Å0.30 × 0.30 × 0.20 mm
Data collection top
Bruker SMART APEX CCD
diffractometer
1457 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2000)
1330 reflections with I > 2σ(I)
Tmin = 0.952, Tmax = 0.968Rint = 0.029
9957 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0271 restraint
wR(F2) = 0.074H-atom parameters constrained
S = 1.08Δρmax = 0.25 e Å3
1457 reflectionsΔρmin = 0.16 e Å3
191 parameters
Special details top

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.

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 (Å2) top
xyzUiso*/Ueq
F10.42776 (14)0.5920 (2)0.07757 (7)0.0454 (3)
F20.69164 (13)0.6496 (2)0.04859 (8)0.0462 (3)
F30.36969 (12)0.3520 (2)0.17285 (7)0.0455 (3)
F40.63344 (13)0.4084 (2)0.20130 (8)0.0468 (3)
O10.20150 (16)0.3642 (2)0.02812 (8)0.0410 (4)
O20.15456 (14)0.5081 (2)0.08150 (8)0.0377 (4)
O30.90284 (14)0.4847 (2)0.04279 (10)0.0407 (4)
H30.98320.49580.05640.061*
O40.85978 (15)0.6410 (3)0.15075 (9)0.0458 (4)
C10.38844 (19)0.4724 (3)0.04701 (12)0.0273 (4)
C20.4755 (2)0.5446 (3)0.00816 (11)0.0297 (4)
C30.6137 (2)0.5735 (3)0.00650 (12)0.0308 (4)
C40.6716 (2)0.5305 (3)0.07715 (12)0.0293 (4)
C50.5845 (2)0.4576 (3)0.13208 (12)0.0301 (4)
C60.4463 (2)0.4288 (3)0.11741 (12)0.0296 (4)
C70.23534 (19)0.4443 (3)0.03141 (11)0.0278 (4)
C80.8223 (2)0.5593 (3)0.09441 (12)0.0303 (4)
N10.1433 (2)0.5881 (3)0.24288 (12)0.0513 (5)
H10.15590.58440.19400.077*
N20.1630 (2)0.6764 (3)0.35864 (12)0.0453 (5)
H20.19440.73500.39790.068*
C90.2114 (3)0.6965 (4)0.28898 (14)0.0514 (6)
H9A0.28280.77510.27480.062*
C100.0465 (3)0.4950 (4)0.28392 (15)0.0527 (6)
H10A0.01600.40900.26490.063*
C110.0584 (3)0.5505 (4)0.35669 (15)0.0540 (7)
H11A0.00560.51100.39810.065*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
F10.0323 (7)0.0729 (9)0.0310 (6)0.0017 (6)0.0050 (5)0.0119 (6)
F20.0278 (6)0.0714 (9)0.0395 (7)0.0075 (6)0.0069 (5)0.0144 (7)
F30.0275 (6)0.0703 (9)0.0386 (7)0.0063 (6)0.0045 (5)0.0152 (7)
F40.0293 (7)0.0746 (9)0.0365 (7)0.0025 (6)0.0063 (5)0.0153 (7)
O10.0272 (7)0.0602 (10)0.0357 (8)0.0000 (7)0.0019 (6)0.0145 (7)
O20.0185 (6)0.0610 (9)0.0336 (7)0.0001 (6)0.0015 (6)0.0128 (7)
O30.0171 (6)0.0628 (9)0.0422 (8)0.0002 (6)0.0007 (6)0.0144 (8)
O40.0295 (8)0.0667 (11)0.0412 (9)0.0031 (7)0.0027 (7)0.0147 (8)
C10.0189 (8)0.0325 (9)0.0304 (9)0.0017 (7)0.0013 (8)0.0036 (7)
C20.0240 (10)0.0388 (10)0.0262 (9)0.0028 (8)0.0023 (8)0.0004 (7)
C30.0224 (9)0.0372 (10)0.0328 (10)0.0005 (8)0.0046 (8)0.0029 (8)
C40.0194 (8)0.0345 (9)0.0341 (10)0.0006 (7)0.0001 (8)0.0024 (8)
C50.0221 (9)0.0390 (10)0.0293 (9)0.0020 (8)0.0005 (8)0.0015 (8)
C60.0209 (9)0.0378 (10)0.0301 (9)0.0005 (8)0.0045 (7)0.0026 (8)
C70.0176 (8)0.0363 (9)0.0296 (10)0.0004 (7)0.0001 (8)0.0009 (7)
C80.0203 (9)0.0376 (9)0.0330 (10)0.0018 (7)0.0006 (8)0.0003 (8)
N10.0480 (12)0.0780 (14)0.0279 (9)0.0091 (10)0.0018 (9)0.0079 (10)
N20.0495 (11)0.0558 (11)0.0304 (8)0.0031 (9)0.0080 (8)0.0100 (8)
C90.0479 (14)0.0661 (15)0.0403 (12)0.0060 (12)0.0003 (12)0.0038 (12)
C100.0513 (15)0.0611 (14)0.0458 (13)0.0049 (13)0.0130 (13)0.0068 (12)
C110.0472 (15)0.0775 (18)0.0371 (12)0.0058 (12)0.0018 (11)0.0066 (12)
Geometric parameters (Å, º) top
F1—C21.339 (2)C4—C51.382 (3)
F2—C31.340 (2)C4—C81.509 (3)
F3—C61.339 (2)C5—C61.382 (3)
F4—C51.343 (2)N1—C91.302 (3)
O1—C71.232 (2)N1—C101.359 (4)
O2—C71.261 (2)N1—H10.8600
O3—C81.308 (3)N2—C91.309 (3)
O3—H30.8199N2—C111.364 (4)
O4—C81.201 (3)N2—H20.8600
C1—C21.382 (3)C9—H9A0.9300
C1—C61.385 (3)C10—C111.334 (4)
C1—C71.526 (3)C10—H10A0.9300
C2—C31.382 (3)C11—H11A0.9300
C3—C41.388 (3)
C8—O3—H3109.4O1—C7—C1118.19 (17)
C2—C1—C6116.88 (16)O2—C7—C1115.81 (18)
C2—C1—C7121.55 (18)O4—C8—O3125.59 (19)
C6—C1—C7121.57 (18)O4—C8—C4121.64 (19)
F1—C2—C1120.78 (17)O3—C8—C4112.77 (18)
F1—C2—C3117.67 (17)C9—N1—C10109.0 (2)
C1—C2—C3121.55 (18)C9—N1—H1123.8
F2—C3—C2118.62 (18)C10—N1—H1127.1
F2—C3—C4119.76 (18)C9—N2—C11108.6 (2)
C2—C3—C4121.59 (18)C9—N2—H2123.6
C5—C4—C3116.73 (17)C11—N2—H2127.8
C5—C4—C8120.63 (19)N1—C9—N2108.7 (3)
C3—C4—C8122.64 (18)N1—C9—H9A125.6
F4—C5—C4120.31 (17)N2—C9—H9A125.6
F4—C5—C6118.02 (18)C11—C10—N1106.9 (2)
C4—C5—C6121.65 (19)C11—C10—H10A126.6
F3—C6—C5117.99 (19)N1—C10—H10A126.6
F3—C6—C1120.39 (18)C10—C11—N2106.8 (2)
C5—C6—C1121.60 (19)C10—C11—H11A126.6
O1—C7—O2126.00 (18)N2—C11—H11A126.6
C6—C1—C2—F1179.39 (17)C4—C5—C6—C10.3 (3)
C7—C1—C2—F10.2 (3)C2—C1—C6—F3177.56 (18)
C6—C1—C2—C30.6 (3)C7—C1—C6—F33.2 (3)
C7—C1—C2—C3178.64 (18)C2—C1—C6—C50.5 (3)
F1—C2—C3—F21.0 (3)C7—C1—C6—C5178.70 (19)
C1—C2—C3—F2177.83 (17)C2—C1—C7—O149.2 (3)
F1—C2—C3—C4179.23 (18)C6—C1—C7—O1131.6 (2)
C1—C2—C3—C40.4 (3)C2—C1—C7—O2130.3 (2)
F2—C3—C4—C5178.10 (19)C6—C1—C7—O248.9 (3)
C2—C3—C4—C50.1 (3)C5—C4—C8—O451.2 (3)
F2—C3—C4—C82.3 (3)C3—C4—C8—O4129.2 (2)
C2—C3—C4—C8179.48 (19)C5—C4—C8—O3127.9 (2)
C3—C4—C5—F4178.45 (18)C3—C4—C8—O351.6 (3)
C8—C4—C5—F41.1 (3)C10—N1—C9—N20.3 (3)
C3—C4—C5—C60.0 (3)C11—N2—C9—N10.5 (3)
C8—C4—C5—C6179.55 (19)C9—N1—C10—C110.1 (3)
F4—C5—C6—F30.6 (3)N1—C10—C11—N20.2 (3)
C4—C5—C6—F3177.86 (18)C9—N2—C11—C100.4 (3)
F4—C5—C6—C1178.71 (17)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O20.862.032.870 (3)164
N2—H2···O1i0.861.892.732 (3)168
O3—H3···O2ii0.821.722.5425 (19)177
C9—H9A···O4iii0.932.363.041 (3)130
C11—H11A···O1iv0.932.553.283 (3)136
Symmetry codes: (i) x+1/2, y+1/2, z+1/2; (ii) x+1, y, z; (iii) x1/2, y+3/2, z; (iv) x, y+1, z+1/2.

Experimental details

Crystal data
Chemical formulaC3H5N2+·C8F4HO4
Mr306.18
Crystal system, space groupOrthorhombic, Pna21
Temperature (K)296
a, b, c (Å)9.716 (3), 7.229 (3), 17.406 (6)
V3)1222.5 (7)
Z4
Radiation typeMo Kα
µ (mm1)0.17
Crystal size (mm)0.30 × 0.30 × 0.20
Data collection
DiffractometerBruker SMART APEX CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2000)
Tmin, Tmax0.952, 0.968
No. of measured, independent and
observed [I > 2σ(I)] reflections
9957, 1457, 1330
Rint0.029
(sin θ/λ)max1)0.651
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.027, 0.074, 1.08
No. of reflections1457
No. of parameters191
No. of restraints1
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.25, 0.16

Computer programs: SMART (Bruker, 2000), SAINT (Bruker, 2000), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···O20.862.032.870 (3)163.7
N2—H2···O1i0.861.892.732 (3)167.8
O3—H3···O2ii0.821.722.5425 (19)176.6
C9—H9A···O4iii0.932.363.041 (3)129.5
C11—H11A···O1iv0.932.553.283 (3)135.8
Symmetry codes: (i) x+1/2, y+1/2, z+1/2; (ii) x+1, y, z; (iii) x1/2, y+3/2, z; (iv) x, y+1, z+1/2.
 

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