





Supporting information
![]() | Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536810003387/ds2017sup1.cif |
![]() | Structure factor file (CIF format) https://doi.org/10.1107/S1600536810003387/ds2017Isup2.hkl |
CCDC reference: 765233
Key indicators
- Single-crystal X-ray study
- T = 100 K
- Mean
(C-C) = 0.002 Å
- R factor = 0.025
- wR factor = 0.056
- Data-to-parameter ratio = 13.1
checkCIF/PLATON results
No syntax errors found
Alert level C PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L= 0.600 53
Alert level G PLAT333_ALERT_2_G Check Large Av C6-Ring C-C Dist. C1 -C3_a 1.44 Ang. PLAT335_ALERT_2_G Check Large C6 Ring C-C Range C1 -C3_a 0.16 Ang. PLAT128_ALERT_4_G Non-standard setting of Space-group P21/c .... P21/n
0 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 1 ALERT level C = Check and explain 3 ALERT level G = General alerts; check 0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 2 ALERT type 2 Indicator that the structure model may be wrong or deficient 0 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
Chloranilic acid was purchased from Loba Chemie, Mumbai, India. X-ray quality crystals were obtained from methanol solution after slow evaporation.
The position of the hydrogen atom was found in the difference Fourier map and both the positional and isotropic thermal parameters weres freely refined.
The crystal structures of various charge-transfer complexes of chloranilic acid have been reported (Gotoh, Asaji et al., 2008; Gotoh, Asaji et al., 2007; Gotoh & Ishida, 2009; Gotoh, Ishikawa, et al., 2006; Ishida, 2004; Ishida & Kashino, 1999). Very recently, a study on the formation of either salts or co-crystals by chloranilic acid with the different organic bases was published (Molčanov & Kojić-Prodić, 2010).
There is a number of structures in the Cambridge Database (Allen, 2002) that contain the chloranilic acid (2,5-dichloro-3,6-dihydroxycyclohexa-2,5-diene-1,4-dione, I - Scheme 1), either as a neutral molecule or as an anion (mono- or di-). Interestingly, the only determination of the structure of the acid itself dates back to 1967 (Andersen, 1967a; hereinafter referred to as KA67). The structure was refined based on the visually estimated intensities of the diffraction spots obtained by means of the Weissenberg equi-inclination method. The quality of this structure is excellent taking into account the technology involved, but - having in mind the importance of this small molecule - thanks to the advancement of the methodology it might be desirable to get the more accurate results. Here we report the results of the structure determination of (I) at 100 (1) K. The unit cell parameters of the accompanying room temperature experiment are in an excellent agreement with the data of KA67, but the model is much better, for instance in terms of R factors (8.9% in 1967, with 22 reflections omitted vs. 2.5% in the present determination), the only symmetry independent hydrogen atom was found in the difference Fourier map in KA67 and left in the position found, while now it was isotropicaly refined, etc. Nevertheless, the basic features of the structure are similar, and both the precision and depth of the analysis in KA67 and accompanying paper on the hydrate (Andersen, 1967b) are really remarkable.
We have chosen to describe the structure in the P21/n space group instead of P21/a used in KA67, in order to have smaller β angle (104.87° instead of 122.77°); the transformation matrix is {-1 0 -1 0 1 0 1 0 0}. The molecule of I lies in the special position, across the center of symmetry (Z'=1/2). The whole molecule is planar (Fig. 1); the maximum deviation form the mean plane through 6 ring atom is 0.0014 (9) Å for the ring atom and 0.029 (3)Å for the other atoms. The bond length pattern confirms the dominant double-bond character for the bonds C3—O3 (1.224 (2) Å) and C1—C2 (1.349 (2) Å) and single-bond for C2—C3 (1.507 (2) Å) and - to the lesser extent - for C1—C3' (1.450 (2) Å).
In the crystal structure the main packing motif arises as the result of relatively strong intermolecular O—H···O hydrogen bonds, which make the antiparallel chains of molecules related by the 21 screw along y direction; using the graph-set notation (Bernstein et al., 1995), these first-order chains will be described as C(5). The neighboring chains are interconnected to give the centrosymmetric second-order rings R44(22) - cf. Fig. 2. These structures produce the one-molecule thick layers of molecules which expand along [101] direction, and the neighboring chains are connected by means of van der Waals interactions and probably also by weak halogen bonds, with Cl···Cl distance of 3.2838 (8)Å and C—Cl···Cl angle of 152.96 (6)° - Fig. 3.
For charge-transfer complexes of chloranilic acid, see: Gotoh et al. (2006, 2007, 2008); Gotoh & Ishida (2009); Ishida (2004); Ishida & Kashino (1999). For a recent study of the formation of either salts or co-crystals by chloranilic acid with different organic bases, see: Molčanov & Kojić-Prodić (2010). For the previous determination fo the title structure, see: Andersen (1967a) and of its hydrate, see: Andersen (1967b). For hydrogen-bond motifs, see: Bernstein et al. (1995). For a description of the Cambridge Structural Database, see: (Allen, 2002). For related literature [on what subject?], see: Al-Attas et al. (2009).
Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Stereochemical Workstation Operation Manual (Siemens, 1989); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).
C6H2Cl2O4 | F(000) = 208 |
Mr = 208.98 | Dx = 2.014 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 4539 reflections |
a = 7.5338 (12) Å | θ = 2.8–27.8° |
b = 5.5225 (10) Å | µ = 0.90 mm−1 |
c = 8.5720 (12) Å | T = 100 K |
β = 104.868 (11)° | Prism, red |
V = 344.70 (10) Å3 | 0.3 × 0.1 × 0.1 mm |
Z = 2 |
Oxford Diffraction Xcalibur Eos diffractometer | 774 independent reflections |
Radiation source: Enhance (Mo) X-ray Source | 698 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.032 |
Detector resolution: 16.1544 pixels mm-1 | θmax = 27.9°, θmin = 3.2° |
ω–scan | h = −9→9 |
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction (2009)) | k = −7→7 |
Tmin = 0.857, Tmax = 1.000 | l = −11→10 |
6154 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.025 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.056 | All H-atom parameters refined |
S = 1.09 | w = 1/[σ2(Fo2) + (0.0204P)2 + 0.3502P] where P = (Fo2 + 2Fc2)/3 |
774 reflections | (Δ/σ)max < 0.001 |
59 parameters | Δρmax = 0.37 e Å−3 |
0 restraints | Δρmin = −0.27 e Å−3 |
C6H2Cl2O4 | V = 344.70 (10) Å3 |
Mr = 208.98 | Z = 2 |
Monoclinic, P21/n | Mo Kα radiation |
a = 7.5338 (12) Å | µ = 0.90 mm−1 |
b = 5.5225 (10) Å | T = 100 K |
c = 8.5720 (12) Å | 0.3 × 0.1 × 0.1 mm |
β = 104.868 (11)° |
Oxford Diffraction Xcalibur Eos diffractometer | 774 independent reflections |
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction (2009)) | 698 reflections with I > 2σ(I) |
Tmin = 0.857, Tmax = 1.000 | Rint = 0.032 |
6154 measured reflections |
R[F2 > 2σ(F2)] = 0.025 | 0 restraints |
wR(F2) = 0.056 | All H-atom parameters refined |
S = 1.09 | Δρmax = 0.37 e Å−3 |
774 reflections | Δρmin = −0.27 e Å−3 |
59 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.8496 (2) | −0.1699 (3) | 0.47066 (18) | 0.0102 (3) | |
Cl1 | 0.66487 (5) | −0.36207 (7) | 0.44138 (4) | 0.01295 (13) | |
C2 | 0.9798 (2) | −0.1990 (3) | 0.38967 (18) | 0.0101 (3) | |
O2 | 0.97189 (15) | −0.3741 (2) | 0.28296 (13) | 0.0132 (3) | |
H2 | 1.064 (3) | −0.381 (4) | 0.249 (3) | 0.034 (7)* | |
C3 | 1.14042 (19) | −0.0274 (3) | 0.41584 (17) | 0.0095 (3) | |
O3 | 1.25301 (15) | −0.0641 (2) | 0.33789 (13) | 0.0126 (2) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0081 (7) | 0.0100 (8) | 0.0122 (7) | −0.0022 (6) | 0.0020 (6) | 0.0014 (6) |
Cl1 | 0.01094 (19) | 0.0138 (2) | 0.0150 (2) | −0.00495 (14) | 0.00488 (13) | −0.00150 (14) |
C2 | 0.0113 (7) | 0.0081 (7) | 0.0102 (7) | 0.0005 (6) | 0.0016 (6) | 0.0013 (6) |
O2 | 0.0121 (5) | 0.0133 (6) | 0.0163 (6) | −0.0014 (4) | 0.0075 (5) | −0.0045 (4) |
C3 | 0.0084 (7) | 0.0103 (7) | 0.0098 (7) | 0.0010 (6) | 0.0021 (6) | 0.0041 (6) |
O3 | 0.0121 (5) | 0.0131 (6) | 0.0147 (5) | 0.0003 (4) | 0.0072 (4) | 0.0008 (4) |
C1—C2 | 1.349 (2) | C2—C3 | 1.508 (2) |
C1—C3i | 1.450 (2) | O2—H2 | 0.82 (2) |
C1—Cl1 | 1.7164 (15) | C3—O3 | 1.2240 (18) |
C2—O2 | 1.3217 (19) | ||
C2—C1—C3i | 121.02 (14) | C1—C2—C3 | 120.71 (14) |
C2—C1—Cl1 | 121.38 (12) | C2—O2—H2 | 112.9 (17) |
C3i—C1—Cl1 | 117.59 (11) | O3—C3—C1i | 124.53 (14) |
O2—C2—C1 | 122.23 (14) | O3—C3—C2 | 117.19 (14) |
O2—C2—C3 | 117.05 (13) | C1i—C3—C2 | 118.27 (13) |
C3i—C1—C2—O2 | −178.48 (14) | O2—C2—C3—O3 | −0.8 (2) |
Cl1—C1—C2—O2 | 0.7 (2) | C1—C2—C3—O3 | −179.74 (14) |
C3i—C1—C2—C3 | 0.4 (2) | O2—C2—C3—C1i | 178.55 (13) |
Cl1—C1—C2—C3 | 179.51 (11) | C1—C2—C3—C1i | −0.4 (2) |
Symmetry code: (i) −x+2, −y, −z+1. |
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H2···O3ii | 0.82 (2) | 2.00 (2) | 2.7516 (15) | 152 (2) |
Symmetry code: (ii) −x+5/2, y−1/2, −z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C6H2Cl2O4 |
Mr | 208.98 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 100 |
a, b, c (Å) | 7.5338 (12), 5.5225 (10), 8.5720 (12) |
β (°) | 104.868 (11) |
V (Å3) | 344.70 (10) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.90 |
Crystal size (mm) | 0.3 × 0.1 × 0.1 |
Data collection | |
Diffractometer | Oxford Diffraction Xcalibur Eos |
Absorption correction | Multi-scan (CrysAlis PRO; Oxford Diffraction (2009)) |
Tmin, Tmax | 0.857, 1.000 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6154, 774, 698 |
Rint | 0.032 |
(sin θ/λ)max (Å−1) | 0.657 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.025, 0.056, 1.09 |
No. of reflections | 774 |
No. of parameters | 59 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.37, −0.27 |
Computer programs: CrysAlis PRO (Oxford Diffraction, 2009), SIR92 (Altomare et al., 1993), SHELXL97 (Sheldrick, 2008), Stereochemical Workstation Operation Manual (Siemens, 1989).
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H2···O3i | 0.82 (2) | 2.00 (2) | 2.7516 (15) | 152 (2) |
Symmetry code: (i) −x+5/2, y−1/2, −z+1/2. |
The crystal structures of various charge-transfer complexes of chloranilic acid have been reported (Gotoh, Asaji et al., 2008; Gotoh, Asaji et al., 2007; Gotoh & Ishida, 2009; Gotoh, Ishikawa, et al., 2006; Ishida, 2004; Ishida & Kashino, 1999). Very recently, a study on the formation of either salts or co-crystals by chloranilic acid with the different organic bases was published (Molčanov & Kojić-Prodić, 2010).
There is a number of structures in the Cambridge Database (Allen, 2002) that contain the chloranilic acid (2,5-dichloro-3,6-dihydroxycyclohexa-2,5-diene-1,4-dione, I - Scheme 1), either as a neutral molecule or as an anion (mono- or di-). Interestingly, the only determination of the structure of the acid itself dates back to 1967 (Andersen, 1967a; hereinafter referred to as KA67). The structure was refined based on the visually estimated intensities of the diffraction spots obtained by means of the Weissenberg equi-inclination method. The quality of this structure is excellent taking into account the technology involved, but - having in mind the importance of this small molecule - thanks to the advancement of the methodology it might be desirable to get the more accurate results. Here we report the results of the structure determination of (I) at 100 (1) K. The unit cell parameters of the accompanying room temperature experiment are in an excellent agreement with the data of KA67, but the model is much better, for instance in terms of R factors (8.9% in 1967, with 22 reflections omitted vs. 2.5% in the present determination), the only symmetry independent hydrogen atom was found in the difference Fourier map in KA67 and left in the position found, while now it was isotropicaly refined, etc. Nevertheless, the basic features of the structure are similar, and both the precision and depth of the analysis in KA67 and accompanying paper on the hydrate (Andersen, 1967b) are really remarkable.
We have chosen to describe the structure in the P21/n space group instead of P21/a used in KA67, in order to have smaller β angle (104.87° instead of 122.77°); the transformation matrix is {-1 0 -1 0 1 0 1 0 0}. The molecule of I lies in the special position, across the center of symmetry (Z'=1/2). The whole molecule is planar (Fig. 1); the maximum deviation form the mean plane through 6 ring atom is 0.0014 (9) Å for the ring atom and 0.029 (3)Å for the other atoms. The bond length pattern confirms the dominant double-bond character for the bonds C3—O3 (1.224 (2) Å) and C1—C2 (1.349 (2) Å) and single-bond for C2—C3 (1.507 (2) Å) and - to the lesser extent - for C1—C3' (1.450 (2) Å).
In the crystal structure the main packing motif arises as the result of relatively strong intermolecular O—H···O hydrogen bonds, which make the antiparallel chains of molecules related by the 21 screw along y direction; using the graph-set notation (Bernstein et al., 1995), these first-order chains will be described as C(5). The neighboring chains are interconnected to give the centrosymmetric second-order rings R44(22) - cf. Fig. 2. These structures produce the one-molecule thick layers of molecules which expand along [101] direction, and the neighboring chains are connected by means of van der Waals interactions and probably also by weak halogen bonds, with Cl···Cl distance of 3.2838 (8)Å and C—Cl···Cl angle of 152.96 (6)° - Fig. 3.