2-Bromo-1,3-bis­(bromo­meth­yl)­benzene, with Z′ = 1.5: whole-mol­ecule disorder of one of the two independent mol­ecules

Kirsop, P.; Storey, J.M.D.; Harrison, W.T.A.

doi:10.1107/S0108270106017707

organic compounds

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 62| Part 7| July 2006| Pages o376-o378

doi:10.1107/S0108270106017707

2-Bromo-1,3-bis(bromomethyl)benzene, with Z′ = 1.5: whole-molecule disorder of one of the two independent molecules

Peter Kirsop,^a John M. D. Storey ^a and William T. A. Harrison ^a ^*

^aDepartment of Chemistry, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, Scotland
^*Correspondence e-mail: w.harrison@abdn.ac.uk

(Received 10 May 2006; accepted 12 May 2006; online 15 June 2006)

The title compound, C₈H₇Br₃, possesses normal geometrical parameters. There are two independent molecules; one shows whole-molecule disorder with respect to an inversion-symmetry-generated partner, while the other is undisordered. This results in the unusual situation of Z′ = 1.5 and Z = 6 for a monoclinic crystal system. The undisordered molecule interacts with its neighbours by way of π–π stacking.

Comment

The title compound, (I), prepared earlier by Newcombe et al. (1977 ), was obtained during our ongoing studies to determine the philicity of aryl radicals by competitive cyclization reactions (Kirsop et al., 2004a ,b ,c ,d ).

There are two independent molecules of (I) (Fig. 1). Both appear to possess their expected geometrical parameters, allowing for the rather low bond precisions obtained in this study. The C1-containing species is unexceptional. With respect to the mean plane of the C1–C6 benzene ring, one of the side-arm terminal Br atoms points `up' [the displacement of Br2 is 1.790 (12) Å] and one points `down' [the displacement of Br3 is −1.792 (12) Å].

The most interesting feature of the structure is the whole-molecule disorder displayed by the C11-containing molecule. This arises from inversion symmetry at the point (1, $[1\over2]$ , $[1\over2]$ ) and symmetry-related locations. The resulting overlapped molecules (Fig. 2) are constrained by symmetry to have equal population parameters of 0.5 for all atoms in the molecule. As with the C1-containing molecule, the two side-arm terminal Br atoms are displaced in opposite senses with respect to the mean plane of the C11–C16 benzene ring [with displacements for Br12 and Br13 of 1.825 (16) and −1.74 (3) Å, respectively]. This situation of one ordered and one disordered molecule results in the atypical situation of Z′ = 1.5 and Z = 6 for a monoclinic system.

As well as van der Waals forces, the crystal packing is influenced by π–π stacking interactions involving the C1-containing molecule (Fig. 3) generated by the c-glide symmetry operation. The Cg⋯Cgⁱ separation [Cg is the centroid of the C1–C6 ring; symmetry code: (i) x, $[{3\over 2}]$ − y, $[{1\over 2}]$ + x] is 3.755 (4) Å and the C1–C6/C1ⁱ–C6ⁱ interplanar separation is 3.411 Å. A PLATON (Spek, 2003 ) analysis of (I) revealed a slightly short Br1⋯Br11ⁱⁱ contact of 3.595 (2) Å [symmetry code: (ii) 2 − x, 1 − y, 1 − z], some 0.1 Å less than the van der Waals radius sum of 3.70 Å (Spek, 2003). Such Br⋯Br contacts are quite common and their significance – specific attractive forces (Desiraju & Parthasarathy, 1989 ) or packing contacts (Eriksson & Hu, 2001 ) – has been debated.

The packing of (I) is shown in Fig. 4, indicating how the ordered and disordered molecules segregate into (010) sheets. Because the C11-containing molecules are almost perpendicular to, and are sandwiched between, the π–π stacks of C1-containing molecules, there can be no π–π forces involving the former molecules [the dihedral angle between the C1–C6 and C11–C16 mean planes is 80.8 (6)°].

Aside from very simple molecules and fragments, whole-molecule disorder (WMD) is not particularly common. A classic example is the 10 π electron molecule azulene, C₁₀H₈, containing fused, planar, five- and seven-membered rings. After several conflicting studies it was concluded (Robertson et al., 1962 ) that azulene shows WMD with the 5/7 and 7/5 conformations overlapped at random. More recently, Ichharam & Boeyens (2001 ) observed WMD in 2-(2-thienyl)-1-(2-pyrazinyl)ethene and 2-(2-thienyl)-1-(2-quinoxalinyl)ethene. In both cases, the disordered components were related by pseudo-twofold axes. Cox & Wardell (2003 ) found WMD in 4,4′-sulfonylbis[N-(4-nitrophenylmethylene)benzenamine], with no (pseudo)symmetry relating the two slightly displaced disorder components.

Figure 1
A view of (I)

, showing 50% probability displacement spheres and ellipsoids (H atoms are drawn as spheres of arbitrary radii).

Figure 2
A detail of (I)

, showing the whole-molecule disorder of the C11-containing molecule (50% probability displacement spheres/ellipsoids; all H atoms have been omitted for clarity). Atoms with the suffix A are generated by the symmetry operation (2 − x, 1 − y, 1 − z).

Figure 3
A detail of (I)

, showing the π–π stacking interaction involving the C1-containing molecule. The molecules containing atoms Br1A and Br1B are generated by the symmetry operations (x, $[{3\over 2}]$ − y, $[{1\over 2}]$ + z) and (x, $[{3\over 2}]$ − y, z − $[{1\over 2}]$ ), respectively.

Figure 4
The packing in (I)

, viewed down [001], with H atoms omitted.

Experimental

2-Bromo-1,3-dimethylbenzene (5.0 g, 0.027 mol), N-bromosuccinamide (NBS, 9.6 g, 0.054 mol) and azobisisobutyronitrile (0.88 g, 0.0054 mol) were added to chloroform (100 ml). The mixture was stirred at reflux under a nitrogen atmosphere for 12 h. After cooling, the mixture was filtered and the solvent was removed at reduced pressure to give a yellow solid. Thin-layer chromatography (hexane) showed 2-bromo-1,3-bis(bromomethyl)benzene as a sharp spot at R_F = 0.21. The NBS residues were removed by flash column chromatography (20:1 hexane–ethyl acetate) and the solvent was removed. The product was washed with hexane, giving a white solid (4.9 g, 53%). A sample was recrystallized from hot hexane–ethyl acetate (20:1) to give clear needles of (I) [m.p. 371–373 K, literature (Newcombe et al., 1977) 374–376 K]. ¹H NMR (CDCl₃): δ_H 4.64 (4H, s, 2 × CH₂), 7.28 (1H, t, J = 8.1 Hz, Ar–H), 7.41 (2H, d, J = 8.1 Hz, 2 × Ar–H); ¹³C NMR (CDCl₃): δ_C 33.8, 126.6, 128.0, 131.3, 138.5.

Crystal data

C₈H₇Br₃
M_r = 342.87
Monoclinic, P 2₁ /c
a = 9.1114 (4) Å
b = 22.6016 (10) Å
c = 7.5004 (3) Å
β = 111.971 (3)°
V = 1432.40 (11) Å³
Z = 6
D_x = 2.385 Mg m⁻³
Mo Kα radiation
μ = 12.61 mm⁻¹
T = 120 (2) K
Blade, colourless
0.60 × 0.10 × 0.01 mm

Data collection

Nonius KappaCCD diffractometer
ω and φ scans
Absorption correction: multi-scan (SORTAV; Blessing, 1995 ) T_min = 0.049, T_max = 0.940 (expected range = 0.046–0.882)
14563 measured reflections
3266 independent reflections
2406 reflections with I > 2σ(I)
R_int = 0.099
θ_max = 27.6°

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.084
wR(F²) = 0.253
S = 1.01
3266 reflections
146 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.1847P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 1.89 e Å⁻³
Δρ_min = −2.79 e Å⁻³

The C1-containing molecule was located and refined straightforwardly. The C11-containing molecule evidently showed massive disorder. By careful analysis of difference maps, the disorder could be resolved into two overlapped symmetry-related molecules of (I) (as described in the Comment). The C atoms of the disordered molecule were refined isotropically. All H atoms were placed in calculated positions (C—H = 0.95–0.99 Å) and refined as riding, with U_iso(H) values of 1.2U_eq(C). The largest difference peak is 1.04 Å from atom Br2 and the deepest difference hole is 0.85 Å from the same atom. Attempts to model the crystal in lower-symmetry space groups were not successful.

Data collection: COLLECT (Nonius, 1998 ); cell refinement: SCALEPACK (Otwinowski & Minor, 1997 ); data reduction: DENZO (Otwinowski & Minor, 1997), SCALEPACK and SORTAV (Blessing, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S0108270106017707/sk3024sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S0108270106017707/sk3024Isup2.hkl

Comment top

The title compound, (I), prepared earlier by Newcombe et al. (1977), arose during our ongoing studies to determine the philicity of aryl radicals by competetive cyclization reactions (Kirsop et al., 2004a,b,c,d).

There are two independent molecules of (I) (Fig. 1). Both appear to possess their expected geometrical parameters, allowing for the rather low bond precisions obtained in this study. The C1-containing species is unexceptional. With respect to the mean plane of the C1–C6 benzene ring, one of the side-arm terminal Br atoms points `up' [the displacement of Br2 = 1.790 (12) Å] and one points `down' [the displacement of Br3 = −1.792 (12) Å].

The most interesting feature of the structure is the whole-molecule disorder displayed by the C11-containing molecule. This arises from inversion symmetry at the point (1, 1/2, 1/2) and symmetry-related locations. The resulting overlapped molecules (Fig. 2) are constrained by symmetry to have equal population parameters of 0.5 for all atoms in the molecule. As with the C1-containing molecule, the two side-arm terminal Br atoms are displaced in opposite senses with respect to the mean plane of the C11–C16 benzene ring [with displacements for Br12 and Br13 of 1.825 (16) and −1.74 (3) Å, respectively]. This situation of one ordered and one disordered molecule results in the atypical situation of Z' = 1.5 and Z = 6 for a monoclinic system.

As well as van der Waals forces, the crystal packing is influenced by π–π stacking interactions involving the C1-containing molecule (Fig. 3) generated by the c-glide symmetry operation. The Cg···Cgⁱ [Cg is the centroid of the C1–C6 ring; symmetry code: (i) x, 3/2 − y, 1/2 + x] separation is 3.755 (4) Å and the C1–C6/C1ⁱ–C6ⁱ inter-planar speration is 3.411 Å. A PLATON (Spek, 2003) analysis of (I) revealed a slightly short Br1···Br11ⁱⁱ contact of 3.595 (2) Å [symmetry code: (ii) 2 − x, 1 − y, 1 − x], some 0.1 Å less than the Br···Br van der Waals radius sum of 3.70 Å (Spek, 2003). Such Br···Br contacts are quite common and their significance – specific attractive forces (Desiraju & Parthasarathy, 1989) or packing contacts (Eriksson & Hu, 2001) – has been debated.

The packing of (I) is shown in Fig. 4, indicating how the ordered and disordered molecules segregate into (010) sheets. Because the C11-containing molecules are almost perpendicular to, and are sandwiched between, the π–π stacks of C1-containing molecules there can be no π–π forces involving the former molecules [the dihedral angle between the C1–C6 and C11–C16 mean planes is 80.8 (6)°].

Aside from very simple molecules and fragments, whole-molecule disorder (WMD) is not particularly common. A classic example is the 10-π electron molecule azulene, C₁₀H₈, containing fused, planar, five- and seven-membered rings. After several conflicting studies it was concluded (Robertson et al., 1962) that azulene shows WMD with the 5/7 and 7/5 conformations overlapped at random. More recently, Ichharam & Boeyens (2001) observed WMD in 2–2(thienyl)-1-(2-pyrazinyl)ethane, C₁₀H₈N₂S, and 2–2(thienyl)-1-(2-quinoxalinyl)ethane, C₁₄H₁₀N₂S. In both cases, the disordered components were related by pseudo-twofold axes. Cox & Wardell (2003) found WMD in 4,4'-sulfonylbis[N-(4-nitrophenylmethylene)benzenamine], C₂₆H₁₈N₄O₆S, with no (pseudo)symmetry relating the two slightly displaced disorder components.

Experimental top

2-Bromo-1,3-dimethylbenzene (5.0 g, 0.027 mol), N-bromosuccinamide (NBS, 9.6 g, 0.054 mol) and azobisisobutyronitrile (AIBN, 0.88 g, 0.0054 mol) were added to chloroform (100 ml). The mixture was stirred at reflux under a nitrogen atmosphere for 12 h. After cooling, the mixture was filtered and the solvent was removed at reduced pressure to give a yellow solid. Thin layer chromatography (hexane) showed 2-bromo-1,3-bis-bromomethyl-benzene as a sharp spot at R_f = 0.21. The NBS residues were removed by flash column chromatography (20:1 hexane–ethyl acetate) and the solvent was removed. The product was washed in hexane giving a white solid (4.9 g, 53%). A sample was recrystallized from hot hexane–ethyl acetate (20:1) to give clear needles of (I) [m.p. 371–373 K, literature (Newcombe et al., 1977) 374–376 K]. ¹H NMR (CDCl₃): δ_H 4.64 (4H, s, 2 × CH₂), 7.28 (1H, t, J = 8.1 Hz, Ar—H), 7.41 (2H, d, J = 8.1 Hz, 2 × Ar—H); ¹³C NMR (CDCl₃): δ_C 33.8, 126.6, 128.0, 131.3, 138.5.

Computing details top

Data collection: Collect (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK, and SORTAV (Blessing, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures top

	Fig. 1. A view of (I), showing 50% probability displacement spheres and ellipsoids (H atoms are drawn as spheres of arbitrary radii).
	Fig. 2. A detail of (I), showing the whole-molecule disorder of the C11-containing molecule (50% displacement spheres/ellipsoids; all H atoms have been omitted for clarity). Atoms with the suffix a are generated by the symmetry operation (2 − x, 1 − y, 1 − z).
	Fig. 3. A detail of (I), showing the π–π stacking interaction involving the C1-containing molecule. The molecules containing Br1a and Btr1b are generated by the symmetry operations (x, 3/2 − y, 1/2 + z) and (x, 3/2 − y, z − 1/2), respectively.
	Fig. 4. The packing in (I), viewed down [001], with H atoms omitted.

2-Bromo-1,3-bis(bromomethyl)benzene top

Crystal data top

C₈H₇Br₃	F(000) = 960
M_r = 342.87	D_x = 2.385 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3208 reflections
a = 9.1114 (4) Å	θ = 2.9–27.5°
b = 22.6016 (10) Å	µ = 12.61 mm⁻¹
c = 7.5004 (3) Å	T = 120 K
β = 111.971 (3)°	Blade, colourless
V = 1432.40 (11) Å³	0.60 × 0.10 × 0.01 mm
Z = 6

Data collection top

Nonius KappaCCD diffractometer	3266 independent reflections
Radiation source: fine-focus sealed tube	2406 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.099
ω and ϕ scans	θ_max = 27.6°, θ_min = 3.0°
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	h = −11→11
T_min = 0.049, T_max = 0.940	k = −28→29
14563 measured reflections	l = −9→9

Refinement top

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)] = 0.084	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.253	H-atom parameters constrained
S = 1.02	w = 1/[σ²(F_o²) + (0.1847P)²] where P = (F_o² + 2F_c²)/3
3266 reflections	(Δ/σ)_max < 0.001
146 parameters	Δρ_max = 1.89 e Å⁻³
18 restraints	Δρ_min = −2.79 e Å⁻³

Crystal data top

C₈H₇Br₃	V = 1432.40 (11) Å³
M_r = 342.87	Z = 6
Monoclinic, P2₁/c	Mo Kα radiation
a = 9.1114 (4) Å	µ = 12.61 mm⁻¹
b = 22.6016 (10) Å	T = 120 K
c = 7.5004 (3) Å	0.60 × 0.10 × 0.01 mm
β = 111.971 (3)°

Data collection top

Nonius KappaCCD diffractometer	3266 independent reflections
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	2406 reflections with I > 2σ(I)
T_min = 0.049, T_max = 0.940	R_int = 0.099
14563 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.084	18 restraints
wR(F²) = 0.253	H-atom parameters constrained
S = 1.02	Δρ_max = 1.89 e Å⁻³
3266 reflections	Δρ_min = −2.79 e Å⁻³
146 parameters

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.

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
C1	0.8454 (10)	0.6929 (4)	0.7788 (10)	0.0206 (17)
C2	0.7173 (10)	0.7232 (4)	0.7914 (10)	0.0178 (15)
C3	0.7214 (11)	0.7863 (4)	0.7936 (11)	0.0195 (17)
H3	0.6339	0.8081	0.7986	0.023*
C4	0.8526 (11)	0.8155 (4)	0.7887 (11)	0.0236 (19)
H4	0.8553	0.8575	0.7923	0.028*
C5	0.9812 (11)	0.7846 (4)	0.7786 (11)	0.0215 (18)
H5	1.0693	0.8058	0.7728	0.026*
C6	0.9828 (10)	0.7233 (4)	0.7768 (10)	0.0198 (17)
C7	0.5713 (11)	0.6931 (4)	0.7972 (11)	0.0237 (18)
H7A	0.5170	0.7201	0.8566	0.028*
H7B	0.6031	0.6573	0.8786	0.028*
C8	1.1180 (12)	0.6912 (4)	0.7647 (12)	0.029 (2)
H8A	1.1779	0.7178	0.7118	0.034*
H8B	1.0790	0.6575	0.6748	0.034*
Br1	0.83970 (12)	0.60963 (4)	0.76676 (13)	0.0314 (3)
Br2	0.42421 (11)	0.67059 (4)	0.54093 (12)	0.0251 (3)
Br3	1.26224 (12)	0.66087 (4)	1.01763 (12)	0.0271 (3)
C11	1.0313 (14)	0.5093 (6)	0.4755 (12)	0.027 (4)*	0.50
C12	1.1455 (11)	0.5068 (5)	0.6607 (14)	0.018 (3)*	0.50
C13	1.1082 (14)	0.4830 (6)	0.8093 (11)	0.028 (3)*	0.50
H13	1.1862	0.4813	0.9358	0.034*	0.50
C14	0.9567 (17)	0.4616 (6)	0.7728 (16)	0.028 (3)*	0.50
H14	0.9312	0.4453	0.8744	0.034*	0.50
C15	0.8425 (12)	0.4640 (6)	0.5877 (19)	0.038 (5)*	0.50
H15	0.7390	0.4493	0.5627	0.045*	0.50
C16	0.8798 (12)	0.4878 (6)	0.4391 (13)	0.029 (4)*	0.50
C17	1.314 (2)	0.5274 (7)	0.719 (2)	0.021 (3)*	0.50
H17A	1.3514	0.5434	0.8514	0.026*	0.50
H17B	1.3198	0.5596	0.6322	0.026*	0.50
C18	0.756 (3)	0.4905 (10)	0.240 (3)	0.042 (5)*	0.50
H18A	0.6996	0.4522	0.2101	0.051*	0.50
H18B	0.8091	0.4962	0.1473	0.051*	0.50
Br11	1.0902 (3)	0.54495 (9)	0.2818 (3)	0.0364 (6)	0.50
Br12	1.4532 (3)	0.46312 (11)	0.7090 (4)	0.0479 (6)	0.50
Br13	0.6022 (3)	0.55394 (10)	0.2047 (4)	0.0465 (6)	0.50

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.025 (5)	0.026 (4)	0.007 (3)	−0.004 (3)	0.001 (3)	0.002 (3)
C2	0.017 (4)	0.026 (3)	0.005 (3)	0.002 (3)	−0.002 (3)	−0.001 (3)
C3	0.023 (4)	0.023 (4)	0.010 (3)	−0.002 (3)	0.004 (3)	−0.002 (3)
C4	0.032 (6)	0.026 (4)	0.014 (4)	−0.003 (4)	0.009 (4)	0.000 (3)
C5	0.021 (5)	0.027 (4)	0.012 (3)	−0.008 (3)	0.001 (3)	0.002 (3)
C6	0.015 (4)	0.034 (4)	0.009 (3)	0.000 (3)	0.002 (3)	0.005 (3)
C7	0.030 (5)	0.027 (4)	0.015 (3)	0.001 (4)	0.009 (3)	0.000 (3)
C8	0.028 (5)	0.037 (5)	0.017 (4)	0.007 (4)	0.004 (4)	0.003 (4)
Br1	0.0344 (7)	0.0214 (5)	0.0355 (6)	0.0023 (4)	0.0097 (5)	−0.0019 (3)
Br2	0.0234 (6)	0.0272 (5)	0.0221 (5)	−0.0053 (3)	0.0056 (4)	−0.0053 (3)
Br3	0.0250 (6)	0.0346 (5)	0.0196 (5)	0.0053 (4)	0.0057 (4)	0.0031 (3)
Br11	0.0602 (17)	0.0251 (10)	0.0256 (10)	0.0130 (9)	0.0181 (11)	0.0065 (8)
Br12	0.0373 (14)	0.0436 (13)	0.0576 (15)	0.0085 (11)	0.0116 (12)	−0.0166 (12)
Br13	0.0413 (15)	0.0288 (11)	0.0500 (14)	0.0072 (10)	−0.0052 (12)	−0.0114 (10)

Geometric parameters (Å, º) top

C1—C2	1.387 (12)	C11—C12	1.3900
C1—C6	1.432 (12)	C11—C16	1.3900
C1—Br1	1.884 (9)	C11—Br11	1.907 (8)
C2—C3	1.426 (12)	C12—C13	1.3900
C2—C7	1.510 (13)	C12—C17	1.51 (2)
C3—C4	1.379 (12)	C13—C14	1.3900
C3—H3	0.9500	C13—H13	0.9500
C4—C5	1.390 (13)	C14—C15	1.3900
C4—H4	0.9500	C14—H14	0.9500
C5—C6	1.386 (12)	C15—C16	1.3900
C5—H5	0.9500	C15—H15	0.9500
C6—C8	1.462 (13)	C16—C18	1.50 (2)
C7—Br2	1.955 (9)	C17—Br12	1.945 (17)
C7—H7A	0.9900	C17—H17A	0.9900
C7—H7B	0.9900	C17—H17B	0.9900
C8—Br3	1.982 (9)	C18—Br13	1.95 (2)
C8—H8A	0.9900	C18—H18A	0.9900
C8—H8B	0.9900	C18—H18B	0.9900

C2—C1—C6	121.6 (8)	C12—C11—C16	120.0
C2—C1—Br1	119.2 (6)	C12—C11—Br11	117.3 (6)
C6—C1—Br1	119.1 (7)	C16—C11—Br11	122.7 (6)
C1—C2—C3	118.4 (8)	C13—C12—C11	120.0
C1—C2—C7	123.5 (8)	C13—C12—C17	114.6 (10)
C3—C2—C7	118.0 (8)	C11—C12—C17	125.4 (10)
C4—C3—C2	119.8 (8)	C12—C13—C14	120.0
C4—C3—H3	120.1	C12—C13—H13	120.0
C2—C3—H3	120.1	C14—C13—H13	120.0
C3—C4—C5	121.1 (9)	C13—C14—C15	120.0
C3—C4—H4	119.4	C13—C14—H14	120.0
C5—C4—H4	119.4	C15—C14—H14	120.0
C6—C5—C4	121.1 (8)	C16—C15—C14	120.0
C6—C5—H5	119.5	C16—C15—H15	120.0
C4—C5—H5	119.5	C14—C15—H15	120.0
C5—C6—C1	117.8 (8)	C15—C16—C11	120.0
C5—C6—C8	120.6 (8)	C15—C16—C18	119.8 (13)
C1—C6—C8	121.5 (8)	C11—C16—C18	120.2 (13)
C2—C7—Br2	112.1 (5)	C12—C17—Br12	111.5 (11)
C2—C7—H7A	109.2	C12—C17—H17A	109.3
Br2—C7—H7A	109.2	Br12—C17—H17A	109.3
C2—C7—H7B	109.2	C12—C17—H17B	109.3
Br2—C7—H7B	109.2	Br12—C17—H17B	109.3
H7A—C7—H7B	107.9	H17A—C17—H17B	108.0
C6—C8—Br3	112.6 (6)	C16—C18—Br13	113.5 (14)
C6—C8—H8A	109.1	C16—C18—H18A	108.9
Br3—C8—H8A	109.1	Br13—C18—H18A	108.9
C6—C8—H8B	109.1	C16—C18—H18B	108.9
Br3—C8—H8B	109.1	Br13—C18—H18B	108.9
H8A—C8—H8B	107.8	H18A—C18—H18B	107.7

C6—C1—C2—C3	2.8 (11)	C16—C11—C12—C13	0.0
Br1—C1—C2—C3	−177.9 (5)	Br11—C11—C12—C13	178.0 (10)
C6—C1—C2—C7	−179.0 (7)	C16—C11—C12—C17	178.7 (13)
Br1—C1—C2—C7	0.4 (10)	Br11—C11—C12—C17	−3.2 (13)
C1—C2—C3—C4	−1.7 (11)	C11—C12—C13—C14	0.0
C7—C2—C3—C4	179.9 (7)	C17—C12—C13—C14	−178.9 (12)
C2—C3—C4—C5	1.0 (11)	C12—C13—C14—C15	0.0
C3—C4—C5—C6	−1.2 (11)	C13—C14—C15—C16	0.0
C4—C5—C6—C1	2.2 (11)	C14—C15—C16—C11	0.0
C4—C5—C6—C8	179.5 (7)	C14—C15—C16—C18	−179.8 (15)
C2—C1—C6—C5	−3.0 (11)	C12—C11—C16—C15	0.0
Br1—C1—C6—C5	177.6 (5)	Br11—C11—C16—C15	−177.9 (11)
C2—C1—C6—C8	179.6 (7)	C12—C11—C16—C18	179.8 (15)
Br1—C1—C6—C8	0.3 (10)	Br11—C11—C16—C18	1.9 (14)
C1—C2—C7—Br2	−81.2 (9)	C13—C12—C17—Br12	86.4 (11)
C3—C2—C7—Br2	97.0 (7)	C11—C12—C17—Br12	−92.4 (12)
C5—C6—C8—Br3	100.6 (8)	C15—C16—C18—Br13	76.6 (16)
C1—C6—C8—Br3	−82.1 (9)	C11—C16—C18—Br13	−103.2 (14)

Experimental details

Crystal data
Chemical formula	C₈H₇Br₃
M_r	342.87
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	120
a, b, c (Å)	9.1114 (4), 22.6016 (10), 7.5004 (3)
β (°)	111.971 (3)
V (Å³)	1432.40 (11)
Z	6
Radiation type	Mo Kα
µ (mm⁻¹)	12.61
Crystal size (mm)	0.60 × 0.10 × 0.01

Data collection
Diffractometer	Nonius KappaCCD diffractometer
Absorption correction	Multi-scan (SORTAV; Blessing, 1995)
T_min, T_max	0.049, 0.940
No. of measured, independent and observed [I > 2σ(I)] reflections	14563, 3266, 2406
R_int	0.099
(sin θ/λ)_max (Å⁻¹)	0.651

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.084, 0.253, 1.02
No. of reflections	3266
No. of parameters	146
No. of restraints	18
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	1.89, −2.79

Computer programs: Collect (Nonius, 1998), HKL SCALEPACK (Otwinowski & Minor, 1997), HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK, and SORTAV (Blessing, 1995), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 (Farrugia, 1997), SHELXL97.

Acknowledgements

The authors thank the EPSRC UK National Crystallography Service for the data collection.

References

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