2,5-Di­bromo-3,6-dimeth­oxycyclo­hexa-2,5-diene-1,4-dione

In the structure of the title compound, C₈H₆Br₂O₄, the complete mol­ecule is generated by the application of a centre of inversion. The mol­ecule is planar (r.m.s. deviation for all non-H atoms but methyl C = 0.0358 Å), with only the methyl groups being deviated from the plane [by ±0.321 (4) Å]. In the crystal packing, Br⋯O(methoxy) halogen bonds [3.2407 (19) Å] connect molecules into supramolecular layers parallel to (101).

Related literature

For the synthesis of the title compound, see: Viault et al. (2011). For the structure of bromanilic acid, see: Robl (1987). For similar structures with a 2,5-cyclo­hexa­diene-1,4-dione core, see: Nakatsuji et al. (2009). For an article dealing with the biological relevance of this type of compound, see: Viault et al. (2013). For papers using the title compound as a synthetic precursor, see: Khan & Driscoll (1976); Tatsuta et al. (2001); Kasahara & Kondo (2006); Gan et al. (2009). For metalla-assemblies obtained with analogous building blocks, see: Gupta et al. (2014); Therrien (2009).

Experimental

Crystal data

• C₈H₆Br₂O₄

• M_r = 325.95

• Monoclinic, P 2₁ /n

• a = 9.4456 (9) Å

• b = 5.4877 (3) Å

• c = 10.0341 (9) Å

• β = 113.846 (7)°

• V = 475.71 (7) ų

• Z = 2

• Mo Kα radiation

• μ = 8.50 mm⁻¹

• T = 173 K

• 0.23 × 0.21 × 0.20 mm

Data collection

• Stoe IPDS diffractometer

• Absorption correction: part of the refinement model (ΔF) (DIFABS; Walker & Stuart, 1983) T_min = 0.246, T_max = 0.704

• 8772 measured reflections

• 1284 independent reflections

• 1144 reflections with I > 2σ(I)

• R_int = 0.071

Refinement

• R[F² > 2σ(F²)] = 0.028

• wR(F²) = 0.067

• S = 1.04

• 1284 reflections

• 65 parameters

• H-atom parameters constrained

• Δρ_max = 0.86 e Å⁻³

• Δρ_min = −0.98 e Å⁻³

Data collection: EXPOSE (Stoe & Cie, 2000); cell refinement: CELL (Stoe & Cie, 2000); data reduction: INTEGRATE (Stoe & Cie, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97.

Supporting information

S1. Structural commentary

Embelin (2,5-di­hydroxy-3-undecyl­cyclo­hexa-2,5-diene-1,4-dione) and its derivatives possess great biological potential (Viault et al., 2013). Over the years, several synthetic strategies have been developed to prepare analogues of Embelin (Khan & Driscoll, 1976; Tatsuta et al., 2001; Kasahara & Kondo, 2006; Gan et al., 2009; Viault et al., 2011), and among the precursors used to synthesize these Embelin derivatives, 2,5-di­bromo-3,6-di­meth­oxy­cyclo­hexa-2,5-diene-1,4-dione (C₈H₆Br₂O₄) is often encountered. Moreover, such 2,5-di­hydroxy-1,4-benzo­quinones are commonly used as building blocks to generate metalla-assemblies (Therrien, 2009; Gupta et al., 2014), which explains our inter­est in the title compound. The molecular structure is presented in Fig. 1.

In the solid-state, the molecule, which sits about an inversion centre, is planar with the methyl groups being only ±0.321 (4) Å out of this plane (the plane defined by the di­bromo­benzo­quinone unit including the two O atoms of the meth­oxy groups has a r.m.s. deviation of 0.0358 Å). The electron delocalization within the cyclo­hexadiene core is reflected in the C—C bonds, which show inter­mediate values instead of the typical C—C and C═C bond distances. A similar pattern of C—C bond distances was observed in the analogous compound bromanilic acid (Robl, 1987) and other substituted 2,5-cyclo­hexadiene-1,4-dione derivatives (Nakatsuji et al., 2009).

S2. Supra­molecular features

In the crystal packing Br···O(meth­oxy) halogen bonds [3.2407 (19) Å] connect molecules into supra­molecular layers parallel to (101).

S3. Synthesis and crystallization

2,5-Di­bromo-3,6-di­meth­oxy­cyclo­hexa-2,5-diene-1,4-dione was prepared according to a published method (Viault et al., 2011). Crystals were obtained by slow evaporation of an ethyl acetate solution containing the title compound.

S4. Refinement

Hydrogen atoms were included in calculated positions and treated as riding atoms, with C—H = 0.96 Å, and with U_iso(H) = 1.5U_eq(C).

Related literature

For the synthesis of the title compound, see: Viault et al. (2011). For the structure of bromanilic acid, see: Robl (1987). For similar structures with a 2,5-cyclohexadiene-1,4-dione core, see: Nakatsuji et al. (2009). For an article dealing with the biological relevance of this type of compound, see: Viault et al. (2013). For papers using the title compound as a synthetic precursor, see: Khan & Driscoll (1976); Tatsuta et al. (2001); Kasahara & Kondo (2006); Gan et al. (2009). For metalla-assemblies obtained with analogous building blocks, see: Gupta et al. (2014); Therrien (2009).

Computing details

Data collection: EXPOSE (Stoe & Cie, 2000); cell refinement: CELL (Stoe & Cie, 2000); data reduction: INTEGRATE (Stoe & Cie, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

Fig. 1. The molecular structure of 2,5-dibromo-3,6-dimethoxy-2,5-cyclohexadiene-1,4-dione (symmetry operation i = -x, 1 - y, 2 - z). Displacement ellipsoids are drawn at the 50% probability level.

2,5-Dibromo-3,6-dimethoxycyclohexa-2,5-diene-1,4-dione

Crystal data

C8H6Br2O4	F(000) = 312
Mr = 325.95	Dx = 2.276 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 7998 reflections
a = 9.4456 (9) Å	θ = 2.4–25.9°
b = 5.4877 (3) Å	µ = 8.50 mm^−1
c = 10.0341 (9) Å	T = 173 K
β = 113.846 (7)°	Block, red
V = 475.71 (7) Å^3	0.23 × 0.21 × 0.20 mm
Z = 2

Data collection

Stoe IPDS diffractometer	1284 independent reflections
Radiation source: fine-focus sealed tube	1144 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.071
Detector resolution: 0 pixels mm^-1	θmax = 29.2°, θmin = 2.5°
ϕ oscillation scans	h = −12→12
Absorption correction: part of the refinement model (ΔF) (DIFABS; Walker & Stuart, 1983)	k = −7→7
Tmin = 0.246, Tmax = 0.704	l = −13→13
8772 measured reflections

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)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.067	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0431P)^2] where P = (Fo^2 + 2Fc^2)/3
1284 reflections	(Δ/σ)max < 0.001
65 parameters	Δρmax = 0.86 e Å^−3
0 restraints	Δρmin = −0.98 e Å^−3

Special details

Experimental. A crystal was mounted at 173 K on a Stoe Image Plate Diffraction System (Stoe & Cie, 2000) using Mo Kα graphite monochromated radiation. Image plate distance 100 mm, ϕ oscillation scans 0 - 180°, step Δϕ = 1.2°, 3 minutes per frame.

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
Br1	0.14128 (3)	0.21073 (5)	0.79296 (3)	0.02303 (10)
C2	−0.0827 (3)	0.2940 (4)	0.9112 (3)	0.0197 (4)
C4	−0.3943 (3)	0.2112 (5)	0.9080 (3)	0.0253 (5)
H4A	−0.4045	0.2467	0.8109	0.038*
H4B	−0.4925	0.2333	0.9138	0.038*
H4C	−0.3608	0.0457	0.9320	0.038*
O2	−0.2815 (2)	0.3740 (4)	1.00971 (19)	0.0262 (4)
O1	−0.1483 (2)	0.1143 (4)	0.8426 (2)	0.0332 (4)
C1	0.0654 (3)	0.3806 (4)	0.9134 (2)	0.0176 (4)
C3	−0.1485 (2)	0.4344 (4)	1.0024 (2)	0.0174 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.02309 (14)	0.02542 (15)	0.02416 (15)	0.00012 (9)	0.01326 (10)	−0.00545 (8)
C2	0.0212 (11)	0.0197 (10)	0.0193 (11)	−0.0009 (8)	0.0093 (9)	−0.0011 (8)
C4	0.0178 (10)	0.0290 (12)	0.0266 (12)	−0.0072 (9)	0.0064 (9)	−0.0016 (9)
O2	0.0216 (8)	0.0326 (9)	0.0283 (9)	−0.0113 (7)	0.0143 (7)	−0.0098 (8)
O1	0.0311 (10)	0.0297 (10)	0.0443 (11)	−0.0119 (8)	0.0209 (9)	−0.0171 (9)
C1	0.0185 (10)	0.0190 (10)	0.0169 (9)	0.0013 (8)	0.0090 (8)	−0.0011 (8)
C3	0.0176 (9)	0.0184 (10)	0.0177 (9)	−0.0004 (8)	0.0086 (8)	0.0012 (7)

Geometric parameters (Å, º)

Br1—C1	1.882 (2)	C4—H4B	0.9600
C2—O1	1.219 (3)	C4—H4C	0.9600
C2—C1	1.469 (3)	O2—C3	1.330 (3)
C2—C3	1.509 (3)	C1—C3^i	1.351 (3)
C4—O2	1.448 (3)	C3—C1^i	1.351 (3)
C4—H4A	0.9600
O1—C2—C1	122.3 (2)	H4B—C4—H4C	109.5
O1—C2—C3	121.0 (2)	C3—O2—C4	123.90 (19)
C1—C2—C3	116.68 (19)	C3^i—C1—C2	124.14 (19)
O2—C4—H4A	109.5	C3^i—C1—Br1	119.87 (16)
O2—C4—H4B	109.5	C2—C1—Br1	115.96 (16)
H4A—C4—H4B	109.5	O2—C3—C1^i	118.4 (2)
O2—C4—H4C	109.5	O2—C3—C2	122.4 (2)
H4A—C4—H4C	109.5	C1^i—C3—C2	119.05 (19)
O1—C2—C1—C3^i	−174.0 (2)	C4—O2—C3—C2	−15.5 (4)
C3—C2—C1—C3^i	4.2 (4)	O1—C2—C3—O2	−1.7 (4)
O1—C2—C1—Br1	4.2 (3)	C1—C2—C3—O2	−179.9 (2)
C3—C2—C1—Br1	−177.59 (16)	O1—C2—C3—C1^i	174.3 (2)
C4—O2—C3—C1^i	168.5 (2)	C1—C2—C3—C1^i	−4.0 (4)

Symmetry code: (i) −x, −y+1, −z+2.