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Crystal structure of 4,4′-di­bromo-2′,5′-dimeth­­oxy-[1,1′-biphen­yl]-2,5-dione (BrHBQBr)

aDepartment of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, AL 35487-0336, USA, and bDepartment of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, Quebec, Canada, H3A 0B8
*Correspondence e-mail: swoski@ua.edu

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 25 September 2015; accepted 28 October 2015; online 4 November 2015)

In the title compound, C14H10Br2O4, the dihedral angle between the aromatic rings is 67.29 (19)°. Both meth­oxy-group C atoms lie close to the plane of their attached ring [deviations = −0.130 (4) and 0.005 (5) Å]. In the crystal, mol­ecules pack in a centrosymmetric fashion and inter­act via a mixture of weak ππ stacking inter­actions [centroid–centoid separations = 4.044 (2) and 4.063 (3) Å], weak C—H⋯O hydrogen bonding, and Br⋯Br halogen bonding. This induces a geometry quite different than that predicted by theory.

1. Chemical context

Biphenyl derivatives have recently been investigated as conductors for single mol­ecule electronic systems (Venkataraman et al., 2006[Venkataraman, L., Klare, J. E., Nuckolls, C., Hybertsen, M. S. & Steigerwald, M. L. (2006). Nature, 442, 904-907.]). Researchers have shown that as the equilibrium twist angle θ between the two rings increases, conduction through the mol­ecule decreases as cos 2(θ). This effect is rationalized as a loss of overlap between two π systems. Inter­rupting conjugation is a prerequisite for the design of unimolecular rectifiers (Aviram & Ratner, 1974[Aviram, A. & Ratner, M. A. (1974). Chem. Phys. Lett. 29, 277-283.]). Biphenyl derivatives with one electron-rich and one electron-deficient ring may be able to bias the direction of electron flow through the mol­ecule, thus acting as a mol­ecular diode. To this end we propose a di­meth­oxy­benzene-quinone structure (`hemibi­quinone', HBQ) as a potential unimolecular device. The asymmetric biphenyl structure should allow for high conductivity through each of the rings, while the dihedral angle between the two rings decreases orbital overlap and allows for partial isolation of the electron-rich donor and electron-poor acceptor moieties.

[Scheme 1]

Two HBQ structures have been previously reported by Taylor et al. (2007[Taylor, S. R., Ung, A. T., Pyne, S. G., Skelton, B. W. & White, A. H. (2007). Tetrahedron, 63, 11377-11385.]) and Zeng & Becker (2004[Zeng, C. & Becker, J. Y. (2004). J. Org. Chem. 69, 1053-1059.]). The mol­ecule described herein is unique in that it possesses bromine substituents on each ring (Fig. 1[link]). The distal halogens allow for high synthetic versatility: these groups can be elaborated sequentially with functional groups to allow deposition in a predictable manner onto a variety of substrates. Originally this mol­ecule was proposed by Love et al. (2009[Love, B. E., Bonner-Stewart, J. & Forrest, L. A. (2009). Synlett, pp. 813-817.]) as an impurity in the synthesis of 4,4′-di­bromo­diquinone; however, characterization of this compound was not reported. We have developed a selective synthesis for this hemibi­quinone that is scalable to gram qu­anti­ties.

[Figure 1]
Figure 1
The mol­ecular structure of the title compound, showing displacement ellipsoids at the 50% probability level.

2. Structural commentary

Because of the crucial role that the twist angle between the rings plays in the electronic properties of the mol­ecule, the determination of the C12—C7—C4—C5 torsion angle is the key observation in this structural analysis. This angle measures −110.9 (4)° in the crystal structure. DFT (B3LYP-DGDZVP) calculations performed on the target mol­ecule in the gas phase predict an angle of −38.54°. This significant discrepancy is probably due to packing inter­actions in the solid phase.

Substituents on the HBQ system behave as expected. The C—Br bond distances reflect the natures of the electron-deficient quinone and electron-rich di­meth­oxy­benzene rings: the C1—Br1 bond distance is 1.872 (5) Å, while the C10—Br2 bond is 1.897 (4) Å. Thus Br1 has a slightly stronger π-donating character into the quinone moiety, strengthening the bond relative to the C10—Br2 bond of the di­meth­oxy­benzene ring. The meth­oxy substituents are nearly coplanar to the benzene ring, with a C12—C11—O4—C14 torsion angle of 1.5 (6)° and a C9—C8—O3—C13 torsion angle of −4.4 (5)°. The methyl portions of each of these groups point away from the sterically restricting groups ortho to these positions. Finally, the quinone ring is slightly buckled (r.m.s. deviation = 0.064 Å), probably due to supra­molecular packing effects.

3. Supra­molecular features

Each mol­ecule is surrounded by eight neighboring mol­ecules, which inter­act through hydrogen bonding, halogen bonding, and ππ inter­actions (Figs. 2[link] and 3[link]). The strongest inter­actions appear to be between functional groups on the quinone ring of one mol­ecule with those on the di­meth­oxy­benzene ring of another. These include especially short but non-directional C—H⋯O hydrogen bonds (Table 1[link]) between the quinone carbonyl groups and di­meth­oxy­benzene ring hydrogen atoms of two neighbors. Inter­actions between like parts of neighboring mol­ecules include edge-to-edge stacking of quinone rings with quinone rings, di­meth­oxy­benzene rings with di­meth­oxy­benzene rings, and dimeric hydrogen bonding between meth­oxy groups. Quinone rings on adjacent mol­ecules along the c axis show some face-to-face π-stacking.

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 and Cg2 are the centroids of the C1–C6 and C7–C12 rings, respectively.

D—H⋯A D—H H⋯A DA D—H⋯A
C9—H9A⋯O2i 0.95 2.40 3.270 (5) 151
C12—H12A⋯O1ii 0.95 2.62 3.461 (5) 148
C13—H13A⋯O4iii 0.98 2.65 3.525 (5) 149
C13—H13BCg2i 0.98 2.57 3.443 (5) 148
C14—H14ACg1iv 0.98 3.00 3.695 (5) 129
Symmetry codes: (i) -x+1, -y+2, -z+1; (ii) -x, -y+2, -z+2; (iii) x, y-1, z; (iv) x, y+1, z.
[Figure 2]
Figure 2
The unit-cell packing of the title compound, viewed down the b axis.
[Figure 3]
Figure 3
Packing diagram showing the stacking of parallel halogen-bonded chains. The view is down the a axis.

Along the a axis, the benzene rings `nestle' closely to one another in an anti­parallel geometry, where one quinone points up and the layer behind it points down. Within the cb plane, the benzene rings are coplanar; hydrogen atoms from C14 on one mol­ecule project closely to O3 on the adjacent mol­ecule and vice versa for a hydrogen atom attached to C13 to the adjacent O4 (Fig. 2[link]). Symmetric C—H⋯π short contacts exist between pairs of C13—H13C⋯di­meth­oxy­benzene (Table 1[link]).

Mol­ecules are aligned linearly in a head-to-tail manner where the bromine atoms participate in Br⋯Br halogen bonding (Fig. 3[link]). As discussed above, Br1 is electron deficient with respect to Br2, and a distinct halogen bond forms along the mol­ecular x-axis (the C7—C4 biphenyl bond). The Br1⋯Br2 separation is 3.4204 (8) Å, with almost linear C1—Br1⋯Br2 and C10—Br2⋯Br1 angles of 178.2 (4) and 170.9 (4)°, respectively. Equivalent rings from mol­ecules packed along this axis are parallel to one another; the quinone and benzene rings aligned coplanar to the corresponding ring in the next mol­ecule.

4. Synthesis and crystallization

Cerium(IV) ammonium nitrate (0.956 g, 1.75 mmol, 1.75 eq) was dissolved in 30 ml of H2O. A solution of 2-bromo-1,4-di­meth­oxy­benzene (0.253 g, 1.17 mmol) in 25 ml of aceto­nitrile was quickly added with vigorous stirring. After three hours, the product had precipitated as a grey–green powder. The precipitate was filtered, washed with water, and dried. The crude product was purified using flash chromatography (silica gel, chloro­form), yielding 0.0959 g of the desired product (20.3%). Crystals were obtained by slow evaporation of a solution in chloro­form.

5. Refinement

Hydrogen atoms were placed in calculated positions, and their coordinates and displacement parameters were constrained to ride on the carrier atom [C—H = 0.98 Å and Uiso(H) = 1.5Ueq(C) for methyl H atoms, C—H = 0.95 Å and Uiso(H) = 1.5Ueq(C) for other H atoms]. Hydrogen atoms on methyl groups were refined with a riding rotating model. Crystal data, data collection and structure refinement details are summarized in Table 2[link].

Table 2
Experimental details

Crystal data
Chemical formula C14H10Br2O4
Mr 402.04
Crystal system, space group Triclinic, P[\overline{1}]
Temperature (K) 173
a, b, c (Å) 7.0909 (6), 9.2120 (8), 10.7056 (10)
α, β, γ (°) 90.989 (3), 97.098 (3), 101.909 (3)
V3) 678.35 (10)
Z 2
Radiation type Mo Kα
μ (mm−1) 5.98
Crystal size (mm) 0.10 × 0.07 × 0.06
 
Data collection
Diffractometer Bruker APEXII CCD
Absorption correction Multi-scan (AXScale; Bruker, 2010[Bruker (2010). APEX2, AXScale and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.])
Tmin, Tmax 0.561, 0.745
No. of measured, independent and observed [I > 2σ(I)] reflections 7453, 2714, 2180
Rint 0.036
(sin θ/λ)max−1) 0.630
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.043, 0.148, 1.04
No. of reflections 2714
No. of parameters 183
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 0.67, −1.06
Computer programs: APEX2 and SAINT (Bruker, 2010[Bruker (2010). APEX2, AXScale and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXS97 and SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]) and SHELXL2014 (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]).

Supporting information


Computing details top

Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT (Bruker, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

4,4'-Dibromo-2',5'-dimethoxy-[1,1'-biphenyl]-2,5-dione top
Crystal data top
C14H10Br2O4Z = 2
Mr = 402.04F(000) = 392
Triclinic, P1Dx = 1.968 Mg m3
a = 7.0909 (6) ÅMo Kα radiation, λ = 0.71073 Å
b = 9.2120 (8) ÅCell parameters from 3169 reflections
c = 10.7056 (10) Åθ = 3.0–26.5°
α = 90.989 (3)°µ = 5.98 mm1
β = 97.098 (3)°T = 173 K
γ = 101.909 (3)°Fragment, brown
V = 678.35 (10) Å30.10 × 0.07 × 0.06 mm
Data collection top
Bruker APEXII CCD
diffractometer
2180 reflections with I > 2σ(I)
φ and ω scansRint = 0.036
Absorption correction: multi-scan
(AXScale; Bruker, 2010)
θmax = 26.6°, θmin = 1.9°
Tmin = 0.561, Tmax = 0.745h = 88
7453 measured reflectionsk = 1111
2714 independent reflectionsl = 1313
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)] = 0.043Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.148H-atom parameters constrained
S = 1.04 w = 1/[σ2(Fo2) + (0.1053P)2]
where P = (Fo2 + 2Fc2)/3
2714 reflections(Δ/σ)max = 0.001
183 parametersΔρmax = 0.67 e Å3
0 restraintsΔρmin = 1.06 e Å3
Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Br10.28348 (7)0.59976 (6)1.11818 (5)0.0442 (2)
Br20.25434 (6)1.33646 (5)0.34039 (4)0.0308 (2)
O10.0292 (5)0.7668 (4)1.0260 (3)0.0365 (8)
O20.5998 (4)0.9672 (4)0.8081 (3)0.0282 (7)
O30.2720 (4)0.8360 (3)0.5689 (3)0.0246 (6)
O40.2214 (4)1.4265 (3)0.6021 (3)0.0272 (7)
C10.2910 (6)0.7438 (5)0.9966 (4)0.0258 (9)
C20.1101 (6)0.8048 (5)0.9676 (4)0.0239 (9)
C30.1079 (6)0.9086 (5)0.8659 (4)0.0240 (9)
H3A0.00540.94760.84490.029*
C40.2593 (6)0.9515 (4)0.8004 (4)0.0189 (8)
C50.4475 (6)0.9059 (5)0.8446 (4)0.0223 (9)
C60.4464 (6)0.7913 (5)0.9381 (4)0.0243 (9)
H6A0.55830.75010.95720.029*
C70.2536 (5)1.0448 (5)0.6908 (4)0.0215 (9)
C80.2612 (5)0.9822 (4)0.5715 (4)0.0196 (8)
C90.2575 (5)1.0693 (4)0.4676 (4)0.0196 (8)
H9A0.26241.02820.38640.024*
C100.2465 (5)1.2161 (5)0.4825 (4)0.0200 (8)
C110.2352 (5)1.2807 (4)0.5986 (4)0.0193 (8)
C120.2373 (5)1.1929 (5)0.7029 (4)0.0207 (8)
H12A0.22751.23400.78330.025*
C130.2659 (6)0.7645 (5)0.4477 (4)0.0241 (9)
H13A0.26590.65900.45800.036*
H13B0.38010.81120.40870.036*
H13C0.14760.77450.39380.036*
C140.2129 (7)1.4946 (5)0.7220 (5)0.0305 (10)
H14A0.19881.59740.71090.046*
H14B0.33271.49380.77810.046*
H14C0.10131.43940.75900.046*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br10.0440 (3)0.0453 (4)0.0449 (4)0.0096 (2)0.0080 (2)0.0305 (3)
Br20.0436 (3)0.0247 (3)0.0258 (3)0.0094 (2)0.0065 (2)0.01177 (19)
O10.0362 (17)0.037 (2)0.041 (2)0.0078 (14)0.0193 (15)0.0106 (15)
O20.0248 (14)0.0329 (18)0.0288 (18)0.0059 (12)0.0101 (12)0.0073 (13)
O30.0345 (16)0.0171 (15)0.0247 (17)0.0089 (12)0.0075 (12)0.0024 (12)
O40.0369 (16)0.0190 (16)0.0287 (18)0.0109 (12)0.0071 (13)0.0038 (13)
C10.031 (2)0.020 (2)0.025 (2)0.0029 (17)0.0031 (17)0.0069 (18)
C20.027 (2)0.023 (2)0.022 (2)0.0014 (16)0.0082 (16)0.0036 (17)
C30.0241 (19)0.019 (2)0.029 (3)0.0056 (16)0.0047 (17)0.0031 (17)
C40.0259 (19)0.016 (2)0.016 (2)0.0052 (15)0.0046 (15)0.0002 (15)
C50.026 (2)0.021 (2)0.020 (2)0.0059 (16)0.0037 (16)0.0010 (16)
C60.028 (2)0.026 (2)0.019 (2)0.0078 (17)0.0007 (16)0.0027 (17)
C70.0158 (17)0.019 (2)0.030 (2)0.0029 (14)0.0052 (15)0.0037 (17)
C80.0177 (17)0.015 (2)0.026 (2)0.0034 (14)0.0042 (15)0.0040 (16)
C90.0176 (17)0.019 (2)0.023 (2)0.0038 (14)0.0047 (15)0.0035 (16)
C100.0157 (17)0.025 (2)0.019 (2)0.0036 (15)0.0024 (14)0.0079 (17)
C110.0169 (17)0.0135 (19)0.028 (2)0.0048 (14)0.0035 (15)0.0052 (16)
C120.0210 (18)0.016 (2)0.025 (2)0.0017 (14)0.0068 (15)0.0011 (16)
C130.026 (2)0.019 (2)0.027 (2)0.0031 (16)0.0047 (16)0.0037 (17)
C140.035 (2)0.020 (2)0.039 (3)0.0101 (18)0.0077 (19)0.003 (2)
Geometric parameters (Å, º) top
Br1—C11.872 (5)C6—H6A0.9500
Br2—C101.897 (4)C7—C121.398 (6)
O1—C21.227 (5)C7—C81.404 (6)
O2—C51.224 (5)C8—C91.384 (6)
O3—C81.365 (5)C9—C101.378 (6)
O3—C131.437 (5)C9—H9A0.9500
O4—C111.367 (5)C10—C111.388 (6)
O4—C141.433 (6)C11—C121.390 (6)
C1—C61.334 (6)C12—H12A0.9500
C1—C21.504 (6)C13—H13A0.9800
C2—C31.462 (6)C13—H13B0.9800
C3—C41.349 (6)C13—H13C0.9800
C3—H3A0.9500C14—H14A0.9800
C4—C71.468 (6)C14—H14B0.9800
C4—C51.504 (6)C14—H14C0.9800
C5—C61.467 (6)
C8—O3—C13117.3 (3)C9—C8—C7119.4 (4)
C11—O4—C14117.8 (3)C10—C9—C8119.7 (4)
C6—C1—C2121.0 (4)C10—C9—H9A120.2
C6—C1—Br1122.8 (4)C8—C9—H9A120.2
C2—C1—Br1116.2 (3)C9—C10—C11122.4 (4)
O1—C2—C3122.1 (4)C9—C10—Br2119.1 (3)
O1—C2—C1121.0 (4)C11—C10—Br2118.5 (3)
C3—C2—C1116.8 (4)O4—C11—C10117.4 (4)
C4—C3—C2123.1 (4)O4—C11—C12124.6 (4)
C4—C3—H3A118.5C10—C11—C12118.0 (4)
C2—C3—H3A118.5C11—C12—C7120.7 (4)
C3—C4—C7123.8 (4)C11—C12—H12A119.7
C3—C4—C5118.4 (4)C7—C12—H12A119.7
C7—C4—C5117.8 (3)O3—C13—H13A109.5
O2—C5—C6120.5 (4)O3—C13—H13B109.5
O2—C5—C4121.1 (4)H13A—C13—H13B109.5
C6—C5—C4118.3 (4)O3—C13—H13C109.5
C1—C6—C5121.2 (4)H13A—C13—H13C109.5
C1—C6—H6A119.4H13B—C13—H13C109.5
C5—C6—H6A119.4O4—C14—H14A109.5
C12—C7—C8119.8 (4)O4—C14—H14B109.5
C12—C7—C4121.3 (4)H14A—C14—H14B109.5
C8—C7—C4118.9 (3)O4—C14—H14C109.5
O3—C8—C9125.2 (4)H14A—C14—H14C109.5
O3—C8—C7115.4 (4)H14B—C14—H14C109.5
Hydrogen-bond geometry (Å, º) top
Cg1 and Cg2 are the centroids of the C1–C6 and C7–C12 rings, respectively.
D—H···AD—HH···AD···AD—H···A
C9—H9A···O2i0.952.403.270 (5)151
C12—H12A···O1ii0.952.623.461 (5)148
C13—H13A···O4iii0.982.653.525 (5)149
C13—H13B···Cg2i0.982.573.443 (5)148
C14—H14A···Cg1iv0.983.003.695 (5)129
Symmetry codes: (i) x+1, y+2, z+1; (ii) x, y+2, z+2; (iii) x, y1, z; (iv) x, y+1, z.
 

Acknowledgements

This research was supported by the National Science Foundation (CHE-08-48206). One of us (JEM) is grateful to the Department of Education's Graduate Assistance in Areas of National Need (GAANN) Program for fellowship support. We appreciate the assistance of Professor David Dixon, Dr Monica Vasiliu and Dr Edward Garner in performing the DFT calculations.

References

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