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Anthraquinone derivatives form an important class of dyes and are also known for their medicinal properties. Recently, 2,3-disubstituted anthraquinones have been shown unexpectedly to jellify various organic solvents. No information on the packing mode of these derivatives was known. Here, the first X-ray structure of a 2,3-disubstituted anthraquinone is reported, namely 2,3-dieth­oxy-9,10-anthraquinone, C18H16O4. The merit of this study lies in the observation of significant differences between the packing in 9,10-anthraquinone, which displays a herring-bone arrangement, and that in the title 2,3-dieth­oxy derivative, in which the mol­ecules lie on parallel crystallographic morror planes separated by a distance of 3.4081 (1) Å, reminiscent of the graphite layer architecture.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270108034227/dn3097sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270108034227/dn3097Isup2.hkl
Contains datablock I

CCDC reference: 710762

Comment top

In recent decades, the field of thermoreversible physical gels formed from low molar mass organogelators (LMOGs; Abdallah & Weiss, 2000) has been the subject of renewed interest (Terech & Weiss, 1997; Weiss & Terech, 2005). A number of new systems (Terech & Weiss, 1997) belonging to a variety of functionalities have been discovered. One class of organogelators, consisting of 2,3-dialkoxy-9,10-anthraquinones, (1n) (see scheme; 8 n 12), was found readily to form yellow gels in ethanol, heptane or acetonitrile (Clavier et al., 1998). These gels are soft materials made of a self-assembled fibrillar network imprisoning a liquid. One of the main questions regarding the structure of these aggregates is best studied by X-ray crystallography (Ostuni et al., 1996; Abdallah et al., 2000; Ballabh et al., 2003). Usually, the gel-forming molecules do not yield good crystals, as was found to be the case for (1n) (8 n 12) [Please check added text]. However, on shortening the chain length (i.e. for n = 2), we obtained single crystals suitable for X-ray analysis. No molecular and crystal structure of any 2,3-disubstituted-9,10-anthraquinones has been determined so far. The first structure of a member of this important series, the title compound, 2,3-diethoxy-9,10-anthraquinone, (12), is reported here and is compared with that of the parent compound to examine how this substitution affects the packing arrangement.

The presence of the two substituents induces a change of crystal space group, from P21/c in the anthraquinone to C2/m in the present work. The molecule is perfectly planar, with all atoms except the H atoms of the methyl groups located in mirror planes (4i) (Fig. 1). It is noticeable that, despite their flexibility, the substituents lie in the anthraquinone substrate plane. Owing to their location in mirror planes parallel to the b axis, the molecules are stacked parallel to each other with an interplanar distance of 3.41(s.u.?) Å. Thus, the molecules form a unidirectional columnar packing, which is reminiscent of the packing of hexagonal graphite (3.40 Å; Pauling, 1945). Such packing results in ππ stacking occurring between the substituted benzene rings, whereas the non-substituted benzenes do not exhibit such an interaction (Table 1, Fig. 2).

The overlap between closest molecules occurs by symmetry around a twofold screw axis. Two consecutive molecules in the same plane exhibit a head-to-tail orientation. This is also the case for closest molecules in the stacking direction. This feature appears clearly in Fig. 2, where four molecules in the unit cell are represented. A salient feature is that the quinoid ring is superimposable on the ethoxy substituents of a neighouring molecule. The intermolecular distance between the O atom of the CO group and the C atom of the ethoxy group O9···C31 = 3.476(s.u.?), and O10···C21 = 3.483(s.u.?) Å, whereas the distance of O9 from the O atom of the ethoxy group O9···O3 = 3.625(s.u.?) Å, and O10···O2 = 3.903(s.u.?) Å. For comparison, the same intermolecular distances between two molecules in the same plane were found to be: O atom of CO group to C atom (CH2) of OCH2CH3 = 3.554(s.u.?) Å; C atom of CO group to O atom of the OCH2CH3 = 5.760(s.u.?) Å. Finally, the calculated O···O distance between the two closest carbonyl groups was found to be 3.752(s.u.?) Å. This value is smaller than the shortest equivalent distance in the anthraquinone lattice.

The crystal structure of the anthraquinone (2) has been determined and redetermined a number of times in order to carry out different analyses, and better refinements have been obtained recently (Fu & Brock, 1998; Slouf, 2002, and references therein). It was found to crystallize in the monoclinic system (space group P21/c) with two molecules per unit cell. Each molecule is arranged around an inversion centre located in the middle of the quinone ring. As seen in Fig. 3, the packing shows a herring-bone arrangement where the two closest molecules are slightly staggered relative to each other and overlap at a distance of 3.49(s.u.?) Å, which is completely different from the title compound. One observes a mutual overlap between the quinoid (central) ring of one molecule and the benzenoid (lateral) ring of the other which results in the formaton of a slipped ππ stacking arrangement (Table 1). In the unit cell, the calculated distances between the closest O atoms are 3.90(s.u.?), 5.14(s.u.?) and 5.19(s.u.?) Å, respectively.

Please give s.u.s for all quoted distances.

Thus, our work has showed that the presence of two ethoxy substituents along the long axis of the 9,10-anthraquinone substrate induces a fundamental change in the molecular arrangement in the crystal, significantly affecting the intermolecular parameters. It seems to be worth examining the influence of chain lengthening on these properties and the possible analogy of (12) with graphite.

Related literature top

For related literature, see: Abdallah & Weiss (2000); Ballabh et al. (2003); Clavier et al. (1998); Desvergne et al. (2005); Fu & Brock (1998); Ostuni et al. (1996); Pauling (1945); Slouf (2002); Terech & Weiss (1997); Weiss & Terech (2005).

Experimental top

The preparation of (12) (m.p. 445 K [343 K in CIF data tables - please clarify]) was described by Desvergne et al. (2005). Single crystals were obtained by slow evaporation of a solution of (12) in a mixture of ethanol and dichloromethane (Solvent ratio?).

Refinement top

H atoms were generated geometrically and treated as riding on their parent atoms, with C—H = 0.93 (aromatic), 0.96 (methyl) or 0.97 Å (methylene) and with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(methyl C).

Computing details top

Data collection: COLLECT (Nonius, 1999); cell refinement: DENZO (Otwinowski & Minor, 1997); data reduction: SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996), ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2003); software used to prepare material for publication: publCIF (Westrip, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of (12), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are represented as small spheres of arbitrary radii.
[Figure 2] Fig. 2. A partial packing view of (12), showing the head-to-tail arrangement of the molecules and the ππ interactions which develop along the b axis. H atoms have been omitted for clarity.
[Figure 3] Fig. 3. A partial packing view of 9,10-anthraquinone, (2), showing the herring-bone arrangement. H atoms have been omitted for clarity.
2,3-diethoxy-9,10-anthraquinone top
Crystal data top
C18H16O4F(000) = 624
Mr = 296.30Dx = 1.310 Mg m3
Monoclinic, C2/mMelting point: 445 K
Hall symbol: -C 2yMo Kα radiation, λ = 0.71073 Å
a = 17.8007 (3) ÅCell parameters from 2934 reflections
b = 6.8163 (2) Åθ = 2–27.5°
c = 13.9992 (3) ŵ = 0.09 mm1
β = 117.809 (1)°T = 293 K
V = 1502.42 (6) Å3Plate, yellow
Z = 40.37 × 0.10 × 0.10 mm
Data collection top
Nonius Kappa CCD
diffractometer
1835 independent reflections
Radiation source: fine-focus sealed tube1376 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.015
Detector resolution: 9 pixels mm-1θmax = 27.4°, θmin = 4.2°
CCD scansh = 2220
Absorption correction: empirical (using intensity measurements)
SCALEPACK (Otwinowski & Minor 1997)
k = 08
Tmin = 0.959, Tmax = 0.989l = 018
3353 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.049Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.149H-atom parameters constrained
S = 1.04 w = 1/[σ2(Fo2) + (0.0912P)2 + 0.1475P]
where P = (Fo2 + 2Fc2)/3
1835 reflections(Δ/σ)max < 0.001
135 parametersΔρmax = 0.23 e Å3
0 restraintsΔρmin = 0.19 e Å3
Crystal data top
C18H16O4V = 1502.42 (6) Å3
Mr = 296.30Z = 4
Monoclinic, C2/mMo Kα radiation
a = 17.8007 (3) ŵ = 0.09 mm1
b = 6.8163 (2) ÅT = 293 K
c = 13.9992 (3) Å0.37 × 0.10 × 0.10 mm
β = 117.809 (1)°
Data collection top
Nonius Kappa CCD
diffractometer
1835 independent reflections
Absorption correction: empirical (using intensity measurements)
SCALEPACK (Otwinowski & Minor 1997)
1376 reflections with I > 2σ(I)
Tmin = 0.959, Tmax = 0.989Rint = 0.015
3353 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0490 restraints
wR(F2) = 0.149H-atom parameters constrained
S = 1.04Δρmax = 0.23 e Å3
1835 reflectionsΔρmin = 0.19 e Å3
135 parameters
Special details top

Experimental. A yellow crystal 0.37 × 0.10 × 0.10 mm was mounted on an Nonius KappaCCD diffractometer and analysed using monochromated Mo Kα X-ray radiation (λ = 0.7073 Å). Crystal is monoclinic; space group C2/m. All non-H atoms were refined anisotropically in F2. H atoms were generated geometrically and treated as riding on their parent atoms with C—H = 0.93 Å(aromatic), 0.96Å (methyl) and 0.97 Å(methylene) with Uiso(H)= 1.2Uiso(C) or Uiso(H)= 1.5Uiso(Cmethyl).

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 (Å2) top
xyzUiso*/UeqOcc. (<1)
C10.17213 (10)0.00000.44422 (13)0.0528 (4)
H10.11370.00000.41910.063*
C20.22587 (10)0.00000.55355 (12)0.0507 (4)
O20.20059 (7)0.00000.63146 (9)0.0611 (4)
C30.31442 (10)0.00000.59182 (12)0.0498 (4)
O30.36107 (7)0.00000.70053 (8)0.0622 (4)
C40.34706 (10)0.00000.51911 (12)0.0512 (4)
H40.40550.00000.54420.061*
C50.29888 (13)0.00000.13948 (15)0.0712 (5)
H50.35720.00000.16350.085*
C5a0.29184 (10)0.00000.40798 (12)0.0479 (4)
C60.24355 (15)0.00000.02997 (15)0.0794 (6)
H60.26490.00000.01930.095*
C6a0.20454 (10)0.00000.37048 (12)0.0494 (4)
C70.15788 (16)0.00000.00623 (15)0.0847 (7)
H70.12090.00000.08000.102*
C80.12629 (14)0.00000.06676 (15)0.0798 (6)
H80.06790.00000.04180.096*
C90.14435 (11)0.00000.25381 (13)0.0573 (4)
O90.06755 (8)0.00000.22070 (10)0.0790 (5)
C9a0.18047 (11)0.00000.17694 (13)0.0579 (4)
C100.32791 (10)0.00000.33156 (13)0.0546 (4)
O100.40435 (8)0.00000.36335 (10)0.0758 (4)
C10a0.26744 (11)0.00000.21405 (12)0.0550 (4)
C210.11112 (11)0.00000.59751 (14)0.0616 (5)
H21A0.08460.11560.55450.074*0.50
H21B0.08460.11560.55450.074*0.50
C220.10190 (13)0.00000.69965 (16)0.0741 (6)
H22A0.04470.03420.68250.111*0.50
H22B0.11480.12820.73170.111*0.50
H22C0.14040.09400.74960.111*0.50
C310.45175 (11)0.00000.74686 (13)0.0670 (5)
H31A0.47120.11560.72450.080*0.50
H31B0.47120.11560.72450.080*0.50
C320.48472 (13)0.00000.86741 (14)0.0849 (7)
H32A0.54380.03490.90240.127*0.50
H32B0.45340.09350.88610.127*0.50
H32C0.47800.12840.89050.127*0.50
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0448 (8)0.0744 (10)0.0428 (8)0.0000.0234 (6)0.000
C20.0534 (9)0.0656 (10)0.0423 (8)0.0000.0300 (7)0.000
O20.0525 (7)0.0978 (9)0.0415 (6)0.0000.0291 (5)0.000
C30.0500 (8)0.0645 (9)0.0370 (7)0.0000.0221 (6)0.000
O30.0502 (6)0.1033 (10)0.0349 (5)0.0000.0214 (5)0.000
C40.0483 (8)0.0688 (10)0.0410 (7)0.0000.0246 (6)0.000
C50.0710 (11)0.1041 (15)0.0497 (9)0.0000.0376 (8)0.000
C5a0.0509 (8)0.0594 (9)0.0392 (7)0.0000.0259 (7)0.000
C60.0900 (15)0.1143 (17)0.0465 (10)0.0000.0424 (10)0.000
C6a0.0493 (8)0.0625 (9)0.0401 (7)0.0000.0240 (7)0.000
C70.0858 (14)0.1293 (19)0.0383 (9)0.0000.0284 (9)0.000
C80.0631 (11)0.1304 (18)0.0426 (9)0.0000.0219 (8)0.000
C90.0498 (8)0.0803 (11)0.0425 (8)0.0000.0220 (7)0.000
O90.0493 (7)0.1367 (13)0.0489 (7)0.0000.0211 (6)0.000
C9a0.0584 (9)0.0783 (11)0.0392 (8)0.0000.0246 (7)0.000
C100.0537 (9)0.0733 (10)0.0438 (8)0.0000.0284 (7)0.000
O100.0525 (7)0.1321 (12)0.0505 (7)0.0000.0306 (6)0.000
C10a0.0582 (10)0.0705 (11)0.0415 (8)0.0000.0277 (8)0.000
C210.0531 (9)0.0890 (12)0.0532 (9)0.0000.0336 (7)0.000
C220.0720 (12)0.1062 (15)0.0638 (11)0.0000.0482 (10)0.000
C310.0499 (9)0.1098 (15)0.0408 (8)0.0000.0206 (7)0.000
C320.0628 (11)0.145 (2)0.0406 (9)0.0000.0188 (8)0.000
Geometric parameters (Å, º) top
C1—C21.375 (2)C7—H70.9300
C1—C6a1.398 (2)C8—C9a1.386 (2)
C1—H10.9300C8—H80.9300
C2—O21.3602 (18)C9—O91.222 (2)
C2—C31.408 (2)C9—C9a1.489 (2)
O2—C211.4339 (19)C9a—C10a1.384 (2)
C3—O31.3515 (18)C10—O101.2186 (19)
C3—C41.388 (2)C10—C10a1.487 (2)
O3—C311.432 (2)C21—C221.513 (2)
C4—C5a1.400 (2)C21—H21A0.9700
C4—H40.9300C21—H21B0.9700
C5—C61.382 (3)C22—H22A0.9600
C5—C10a1.396 (2)C22—H22B0.9600
C5—H50.9300C22—H22C0.9600
C5a—C6a1.389 (2)C31—C321.506 (2)
C5a—C101.482 (2)C31—H31A0.9700
C6—C71.364 (3)C31—H31B0.9700
C6—H60.9300C32—H32A0.9600
C6a—C91.477 (2)C32—H32B0.9600
C7—C81.377 (3)C32—H32C0.9600
C2—C1—C6a120.62 (14)C6a—C9—C9a117.64 (15)
C2—C1—H1119.7C10a—C9a—C8119.56 (16)
C6a—C1—H1119.7C10a—C9a—C9120.87 (14)
O2—C2—C1125.01 (14)C8—C9a—C9119.56 (17)
O2—C2—C3115.17 (13)O10—C10—C5a121.49 (14)
C1—C2—C3119.82 (13)O10—C10—C10a120.83 (14)
C2—O2—C21117.78 (12)C5a—C10—C10a117.68 (14)
O3—C3—C4125.35 (14)C9a—C10a—C5119.19 (15)
O3—C3—C2114.76 (12)C9a—C10a—C10121.37 (13)
C4—C3—C2119.89 (13)C5—C10a—C10119.44 (16)
C3—O3—C31118.73 (12)O2—C21—C22106.26 (14)
C3—C4—C5a119.87 (14)O2—C21—H21A110.5
C3—C4—H4120.1C22—C21—H21A110.5
C5a—C4—H4120.1O2—C21—H21B110.5
C6—C5—C10a120.17 (18)C22—C21—H21B110.5
C6—C5—H5119.9H21A—C21—H21B108.7
C10a—C5—H5119.9C21—C22—H22A109.5
C6a—C5a—C4120.12 (14)C21—C22—H22B109.5
C6a—C5a—C10120.80 (14)H22A—C22—H22B109.5
C4—C5a—C10119.08 (14)C21—C22—H22C109.5
C7—C6—C5120.44 (17)H22A—C22—H22C109.5
C7—C6—H6119.8H22B—C22—H22C109.5
C5—C6—H6119.8O3—C31—C32105.97 (14)
C5a—C6a—C1119.69 (14)O3—C31—H31A110.5
C5a—C6a—C9121.63 (14)C32—C31—H31A110.5
C1—C6a—C9118.69 (14)O3—C31—H31B110.5
C6—C7—C8119.80 (17)C32—C31—H31B110.5
C6—C7—H7120.1H31A—C31—H31B108.7
C8—C7—H7120.1C31—C32—H32A109.5
C7—C8—C9a120.8 (2)C31—C32—H32B109.5
C7—C8—H8119.6H32A—C32—H32B109.5
C9a—C8—H8119.6C31—C32—H32C109.5
O9—C9—C6a121.70 (15)H32A—C32—H32C109.5
O9—C9—C9a120.65 (15)H32B—C32—H32C109.5
C6a—C1—C2—O2180.0C5a—C6a—C9—C9a0.0
C6a—C1—C2—C30.0C1—C6a—C9—C9a180.0
C1—C2—O2—C210.0C7—C8—C9a—C10a0.0
C3—C2—O2—C21180.0C7—C8—C9a—C9180.0
O2—C2—C3—O30.0O9—C9—C9a—C10a180.0
C1—C2—C3—O3180.0C6a—C9—C9a—C10a0.0
O2—C2—C3—C4180.0O9—C9—C9a—C80.0
C1—C2—C3—C40.0C6a—C9—C9a—C8180.0
C4—C3—O3—C310.0C6a—C5a—C10—O10180.0
C2—C3—O3—C31180.0C4—C5a—C10—O100.0
O3—C3—C4—C5a180.0C6a—C5a—C10—C10a0.0
C2—C3—C4—C5a0.0C4—C5a—C10—C10a180.0
C3—C4—C5a—C6a0.0C8—C9a—C10a—C50.0
C3—C4—C5a—C10180.0C9—C9a—C10a—C5180.0
C10a—C5—C6—C70.0C8—C9a—C10a—C10180.0
C4—C5a—C6a—C10.0C9—C9a—C10a—C100.0
C10—C5a—C6a—C1180.0C6—C5—C10a—C9a0.0
C4—C5a—C6a—C9180.0C6—C5—C10a—C10180.0
C10—C5a—C6a—C90.0O10—C10—C10a—C9a180.0
C2—C1—C6a—C5a0.0C5a—C10—C10a—C9a0.0
C2—C1—C6a—C9180.0O10—C10—C10a—C50.0
C5—C6—C7—C80.0C5a—C10—C10a—C5180.0
C6—C7—C8—C9a0.0C2—O2—C21—C22180.0
C5a—C6a—C9—O9180.0C3—O3—C31—C32180.0
C1—C6a—C9—O90.0

Experimental details

Crystal data
Chemical formulaC18H16O4
Mr296.30
Crystal system, space groupMonoclinic, C2/m
Temperature (K)293
a, b, c (Å)17.8007 (3), 6.8163 (2), 13.9992 (3)
β (°) 117.809 (1)
V3)1502.42 (6)
Z4
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.37 × 0.10 × 0.10
Data collection
DiffractometerNonius Kappa CCD
diffractometer
Absorption correctionEmpirical (using intensity measurements)
SCALEPACK (Otwinowski & Minor 1997)
Tmin, Tmax0.959, 0.989
No. of measured, independent and
observed [I > 2σ(I)] reflections
3353, 1835, 1376
Rint0.015
(sin θ/λ)max1)0.647
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.049, 0.149, 1.04
No. of reflections1835
No. of parameters135
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.23, 0.19

Computer programs: COLLECT (Nonius, 1999), DENZO (Otwinowski & Minor, 1997), SCALEPACK (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEPIII (Burnett & Johnson, 1996), ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2003), publCIF (Westrip, 2008).

Comparison of ππ stacking parameters in the title compound, (12), and in the anthraquinone, (2). top
Centroid-to-centroid (Å)Interplanar distance (Å)Slippage (°)
Compound 12
Cg1···Cg1i (substituted benzene rings)3.4879 (2)3.4080.747
Compound 2
Cg1···Cg1ii (quinone rings)3.8961 (6)3.4761.761
Cg1···Cg2iii (quinone–benzene rings)3.5616 (6)3.4810.876
[Symmetry codes: (i) 1/2-x, 1/2+y, 1-z; (ii) 2-x, 1-y, 2-z; (iii) x, y-1, z]. (ii) and (iii) are the symmetry codes for compound (2) in the space group P21/c.
 

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