(5Z,7Z,9Z)-5,10-Di­bromo­benzo[8]annulene

In the structure of the title compound, C₁₂H₈Br₂, the two bromine substituents are oriented exo to the boat-shaped cyclo­octa­tetra­ene at the two ring sites that are β to the ring fusion positions. The average Br—C bond distance is 1.919 (2) Å, the average distance for C=C double bonds that are Br substituted is 1.328 (2) Å, while the other two double-bond distances are 1.327 (2) and 1.398 (2) Å for the non-fused and fused bonds, respectively. Each type of ring inter­atomic distance is within s.u. of the average values for the four known structures, including the title compound, of benzo-fused cyclo­ocata­tetra­enes that are not coordinated to a metal atom. The crystal structure features short Br⋯Br [3.6620 (3) Å] and C⋯H [2.834 (2) and 2.841 (2) Å] contacts.

Related literature

For general background to photochemical conversions of benzo­cyclo­octa­tetra­enes, see: Bender et al. (1982, 1986, 1988, 1991). For details of the synthesis, see: Barton et al. (1964). For related structures, see: Bohshar et al. (1984); Çelik et al. (2002); Jones et al. (1994), Kidokoro et al. (1983); Li et al. (1983). For a description of the Cambridge Structural Database, see: Allen (2002). For the PLATON suite of crystallographic software, see: Spek (2009).

Experimental

Crystal data

• C₁₂H₈Br₂

• M_r = 312.00

• Monoclinic, P 2₁ /c

• a = 8.5289 (5) Å

• b = 8.3630 (5) Å

• c = 15.5645 (9) Å

• β = 105.2980 (6)°

• V = 1070.83 (11) ų

• Z = 4

• Mo Kα radiation

• μ = 7.52 mm⁻¹

• T = 173 K

• 0.16 × 0.09 × 0.08 mm

Data collection

• Bruker APEXII CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2008) T_min = 0.510, T_max = 0.746

• 15053 measured reflections

• 2426 independent reflections

• 2217 reflections with I > 2σ(I)

• R_int = 0.023

Refinement

• R[F² > 2σ(F²)] = 0.017

• wR(F²) = 0.039

• S = 1.04

• 2426 reflections

• 127 parameters

• H-atom parameters constrained

• Δρ_max = 0.49 e Å⁻³

• Δρ_min = −0.46 e Å⁻³

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT-Plus (Bruker, 2008); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXD (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Supporting information

S1. Comment

The title compound was prepared as a starting material for synthesis of the corresponding dinitrile derivative, which was of interest in connection with studies of the photochemical conversions of benzocyclooctatetraenes (Bender et al., 1982; 1986; 1988; 1991). In view of the paucity of structures that are crystallographically established for mono-benzofused cyclo-octatetraenes, we decided to undertake a crystallographic study of (I).

Only three prior structures have been reported which contain one benzo-fused cyclooctatetraene ring according to the Cambridge Structural Database (Allen, 2002; WebCSD, August 2013), excluding those with rings coordinated to metals. The parent hydrocarbon, (5Z,7Z,9Z)-benzo[8]annulene (refcode BUYYUP), has been structurally characterized by X-ray crystallography and investigated by semi-empirical quantum mechanical methods (Li et al., 1983). The only halogen-substituted example is (8-chlorobenzocyclooctatetraen-6-yl)-diphenylphosphine-oxide (refcode: CUDYUV) but this ring bears a large Ph₂P=O substituent; this structure contains two independent molecules in the asymetric unit (Bohshar et al., 1984). In dimethyl 1,4,6,9-tetramethylbenzocyclooctatetraene-5,10-dicarboxylate (refcode: LEZMAE) the two methyl ester substituents are located where the Br atoms are in (I) but this molecule also has four methyl substituents, two attached to the other ends of the same double bonds that the esters are attached to, and two in the 1 and 4 positions of the benzene rings (Jones et al., 1994). Gratifyingly, all the 1,2 interatomic distances in (I) are found to lie within s.u. of the average values from these three comparison structures and (I).

Related benzo-fused cyclooctatrienes which have the same 5,8-dibromo substitution as found in (I) have been structurally characterized. In 5,8,10-tribromo-(8H)-benzocycloocten-7-one (refcode: BOGWAV) the cyclooctatriene ring is distorted by saturation at C8 and a ketone group at C7 (Kidokoro et al., 1983), whilst 5,7,7,8,10-pentabromo-7,8-dihydrobenzocyclooctene (refcode: FABDOC) has C7 with two Br and C8 with H and Br substituents (Çelik et al., 2002). The C5-Br1 and C10-Br2 distances in BOGWAV are 1.8822 (3) and 1.9309 (3) Å and in FABDOC 1.912 (7) and 1.896 (9). Thus the average C-Br bond distance in this set of three related structures is 1.910 (16) Å, with the distances in (I) found within s.u. of this value.

In the crystal structure of (I) molecules are tightly packed. There are three unique short intermolecular contacts (Figure 2), namely C2···H7ⁱ = H7···C2ⁱⁱ = 2.834 (2) Å, Br1···Br2ⁱⁱⁱ = 3.6620 (3) Å and C9···H1^iv = 2.841 (2) Å (symcodes employed: i, 1-x,-1/2+y,1/2-z; ii, 1-x,1/2+y,1/2-z; iii, -x,1-y,-z; iv, 1-x,-y,-z).

Related literature

For general background to photochemical conversions of benzocyclooctatetraenes, see: Bender et al. (1982, 1986, 1988, 1991). For details of the synthesis, see: Barton et al. (1964). For related structures, see: Bohshar et al. (1984); Çelik et al. (2002); Jones et al. (1994), Kidokoro et al. (1983); Li et al. (1983). For a description of the Cambridge Structural Database, see: Allen (2002). For the PLATON suite of crystallographic software, see: Spek (2009).

S2. Experimental

Samples of (I) were prepared from biphenylene via the method of Barton et al. (1964). Crystals were obtained from aqueous methanol (m.p. 366–368 K).

S3. Refinement

All the hydrogen atoms were located on a difference map, but for purposes of refinement are treated as riding on their attached aromatic carbon atoms with C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT-Plus (Bruker, 2008); data reduction: SAINT-Plus (Bruker, 2008); program(s) used to solve structure: SHELXD (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. Molecular structure of (I) drawn with displacement elipsoids at the 40% probability level, and also showing the atom numbering scheme.
	Fig. 2. View along the a axis (with b horizontal and c vertical) showing the three unique intermolecular contacts (as dashed-line tubes) that are less than the sums of the v.d. Waals' radii of the interacting atoms. (Symcodes: i, 1-x,-1/2+y,1/2-z; ii, 1-x,1/2+y,1/2-z; iii, -x,1-y,-z; iv, 1-x,-y,-z.)

(5Z,7Z,9Z)-5,10-Dibromobenzo[8]annulene

Crystal data

C12H8Br2	Dx = 1.935 Mg m^−3
Mr = 312.00	Melting point: 366 K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.5289 (5) Å	Cell parameters from 9956 reflections
b = 8.3630 (5) Å	θ = 2.5–29.0°
c = 15.5645 (9) Å	µ = 7.52 mm^−1
β = 105.2980 (6)°	T = 173 K
V = 1070.83 (11) Å^3	Block, colourless
Z = 4	0.16 × 0.09 × 0.08 mm
F(000) = 600

Data collection

Bruker APEXII CCD area-detector diffractometer	2426 independent reflections
Radiation source: fine-focus sealed tube, Bruker D8	2217 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
Detector resolution: 66.06 pixels mm^-1	θmax = 27.4°, θmin = 2.5°
ϕ and ω scans	h = −11→11
Absorption correction: multi-scan (SADABS; Bruker, 2008)	k = −10→10
Tmin = 0.510, Tmax = 0.746	l = −20→20
15053 measured reflections

Refinement

Refinement on F^2	Primary atom site location: dual
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.017	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.039	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0171P)^2 + 0.5892P] where P = (Fo^2 + 2Fc^2)/3
2426 reflections	(Δ/σ)max = 0.001
127 parameters	Δρmax = 0.49 e Å^−3
0 restraints	Δρmin = −0.46 e Å^−3

Special details

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. Structure first solved in P2₁; used the PLATON "Addsym" tool to find the true space group and refinement continued in P2₁/c (Spek, 2009).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.00196 (2)	0.47441 (2)	0.12658 (2)	0.02901 (6)
Br2	0.33582 (2)	0.24542 (2)	−0.10638 (2)	0.02977 (6)
C1	0.2640 (2)	−0.0177 (2)	0.03420 (12)	0.0251 (4)
H1	0.3169	−0.0572	−0.0081	0.030*
C2	0.1703 (2)	−0.1200 (2)	0.06965 (13)	0.0289 (4)
H2	0.1598	−0.2291	0.0522	0.035*
C3	0.0918 (2)	−0.0629 (2)	0.13055 (12)	0.0287 (4)
H3	0.0285	−0.1332	0.1557	0.034*
C4	0.1056 (2)	0.0963 (2)	0.15478 (11)	0.0240 (4)
H4	0.0496	0.1351	0.1958	0.029*
C4A	0.20053 (19)	0.2013 (2)	0.11986 (10)	0.0187 (3)
C5	0.2100 (2)	0.3709 (2)	0.14745 (11)	0.0210 (3)
C6	0.3398 (2)	0.4538 (2)	0.19030 (12)	0.0264 (4)
H6	0.3235	0.5615	0.2054	0.032*
C7	0.5062 (2)	0.3917 (2)	0.21606 (12)	0.0282 (4)
H7	0.5615	0.3944	0.2776	0.034*
C8	0.5866 (2)	0.3322 (2)	0.16108 (12)	0.0270 (4)
H8	0.6935	0.2938	0.1867	0.032*
C9	0.5240 (2)	0.3205 (2)	0.06401 (12)	0.0239 (4)
H9	0.5851	0.3714	0.0289	0.029*
C10	0.3892 (2)	0.2449 (2)	0.02106 (11)	0.0206 (3)
C10A	0.28235 (19)	0.1430 (2)	0.05945 (11)	0.0187 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.02787 (10)	0.02768 (10)	0.03510 (11)	0.00464 (7)	0.01468 (8)	−0.00192 (8)
Br2	0.02890 (10)	0.04284 (12)	0.01930 (9)	0.00265 (8)	0.00940 (7)	0.00122 (7)
C1	0.0269 (9)	0.0217 (9)	0.0237 (9)	0.0048 (7)	0.0016 (7)	−0.0011 (7)
C2	0.0294 (9)	0.0177 (9)	0.0326 (10)	−0.0018 (7)	−0.0041 (8)	0.0015 (8)
C3	0.0240 (9)	0.0264 (10)	0.0308 (10)	−0.0070 (7)	−0.0016 (7)	0.0094 (8)
C4	0.0202 (8)	0.0286 (9)	0.0229 (8)	−0.0020 (7)	0.0052 (7)	0.0032 (7)
C4A	0.0173 (7)	0.0198 (8)	0.0170 (8)	−0.0005 (6)	0.0012 (6)	0.0014 (6)
C5	0.0233 (8)	0.0227 (9)	0.0193 (8)	0.0011 (7)	0.0098 (6)	0.0007 (7)
C6	0.0338 (10)	0.0236 (9)	0.0233 (9)	−0.0048 (8)	0.0101 (7)	−0.0057 (7)
C7	0.0277 (9)	0.0325 (10)	0.0214 (9)	−0.0114 (8)	0.0015 (7)	0.0010 (8)
C8	0.0200 (8)	0.0298 (10)	0.0287 (9)	−0.0054 (7)	0.0019 (7)	0.0055 (8)
C9	0.0223 (8)	0.0252 (9)	0.0269 (9)	0.0008 (7)	0.0111 (7)	0.0039 (7)
C10	0.0227 (8)	0.0228 (9)	0.0178 (8)	0.0063 (7)	0.0081 (6)	0.0011 (6)
C10A	0.0171 (7)	0.0192 (8)	0.0174 (8)	0.0009 (6)	0.0006 (6)	0.0019 (6)

Geometric parameters (Å, º)

Br1—C5	1.9234 (17)	C4A—C5	1.478 (2)
Br2—C10	1.9145 (17)	C5—C6	1.327 (2)
C1—C2	1.382 (3)	C6—C7	1.465 (3)
C1—C10A	1.397 (2)	C6—H6	0.9500
C1—H1	0.9500	C7—C8	1.326 (3)
C2—C3	1.381 (3)	C7—H7	0.9500
C2—H2	0.9500	C8—C9	1.467 (3)
C3—C4	1.380 (3)	C8—H8	0.9500
C3—H3	0.9500	C9—C10	1.327 (2)
C4—C4A	1.398 (2)	C9—H9	0.9500
C4—H4	0.9500	C10—C10A	1.484 (2)
C4A—C10A	1.398 (2)
C2—C1—C10A	121.12 (17)	C5—C6—C7	124.91 (17)
C2—C1—H1	119.4	C5—C6—H6	117.5
C10A—C1—H1	119.4	C7—C6—H6	117.5
C3—C2—C1	119.75 (17)	C8—C7—C6	125.79 (16)
C3—C2—H2	120.1	C8—C7—H7	117.1
C1—C2—H2	120.1	C6—C7—H7	117.1
C4—C3—C2	119.95 (17)	C7—C8—C9	125.45 (17)
C4—C3—H3	120.0	C7—C8—H8	117.3
C2—C3—H3	120.0	C9—C8—H8	117.3
C3—C4—C4A	121.04 (17)	C10—C9—C8	125.57 (16)
C3—C4—H4	119.5	C10—C9—H9	117.2
C4A—C4—H4	119.5	C8—C9—H9	117.2
C10A—C4A—C4	119.05 (16)	C9—C10—C10A	127.81 (16)
C10A—C4A—C5	122.07 (15)	C9—C10—Br2	117.29 (13)
C4—C4A—C5	118.88 (15)	C10A—C10—Br2	114.52 (12)
C6—C5—C4A	128.45 (16)	C1—C10A—C4A	119.06 (16)
C6—C5—Br1	117.39 (13)	C1—C10A—C10	118.30 (15)
C4A—C5—Br1	113.91 (12)	C4A—C10A—C10	122.64 (15)
C10A—C1—C2—C3	0.6 (3)	C7—C8—C9—C10	−57.1 (3)
C1—C2—C3—C4	0.9 (3)	C8—C9—C10—C10A	−6.8 (3)
C2—C3—C4—C4A	−1.2 (3)	C8—C9—C10—Br2	−179.26 (14)
C3—C4—C4A—C10A	0.0 (2)	C2—C1—C10A—C4A	−1.7 (2)
C3—C4—C4A—C5	179.50 (16)	C2—C1—C10A—C10	177.97 (15)
C10A—C4A—C5—C6	−62.3 (2)	C4—C4A—C10A—C1	1.4 (2)
C4—C4A—C5—C6	118.2 (2)	C5—C4A—C10A—C1	−178.05 (15)
C10A—C4A—C5—Br1	123.72 (14)	C4—C4A—C10A—C10	−178.29 (15)
C4—C4A—C5—Br1	−55.72 (18)	C5—C4A—C10A—C10	2.3 (2)
C4A—C5—C6—C7	2.9 (3)	C9—C10—C10A—C1	−118.0 (2)
Br1—C5—C6—C7	176.62 (14)	Br2—C10—C10A—C1	54.57 (18)
C5—C6—C7—C8	58.2 (3)	C9—C10—C10A—C4A	61.7 (2)
C6—C7—C8—C9	1.3 (3)	Br2—C10—C10A—C4A	−125.75 (14)