2,4-Di­bromo­phenyl 2,6-di­bromo­phenyl ether

The title compound, C₁₂H₆Br₄O, is the fourth well characterized of a total of potentially 209 different brominated di­phenyl ethers. Salient intermolecular interactions are between ether O and aromatic C atoms, and between a bromine substituent and the aromatic ring system.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.007 Å
• R factor = 0.029
• wR factor = 0.056
• Data-to-parameter ratio = 17.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

The title compound, (I), belongs to a class of compounds known as brominated diphenyl ethers (DE's) which are used as flame retardants. Commercially available mixtures mainly consist of highly brominated congeners, such as decabromodiphenyl ether (Eriksson et al., 1999). The occurrence in the environment of less brominated congeners are dependent on both primary sources and decomposition from higher brominated DE's (Eriksson et al., 2001). The crystal structure and packing pattern of these compounds are of fundamental importance in order to model the reaction mechanism in solid state reaction, e.g. flame retardants adsorbed on soot particles.

Both aromatic rings of the title compound are planar within less than 0.01 Å. The deviation of the substituents from the ring plane of the first ring (C1–C6) are 0.050 (7) Å for O and 0.031 (8) Å for Br4, while the Br3 is within the ring plane. The substituents of the second ring (C7 → C12) all deviate significantly from the ring plane: O 0.016 (6) Å, Br1 0.110 (7) Å and Br2 0.053 (7) Å. The angle between the two ring planes is 89.1 (2)°.

Assuming that the aromatic rings of the molecule are ring1 = C1–C6 and ring2 = C7–C12, then the structure can be described as a packing of molecules with close contacts between symmetry-equivalent ring1 systems (C1–C6)···(C1–C6)ⁱ etc. [symmetry code: (i) -0.5 - x, 0.5 + y, -0.5 - z]. Each of the neighbouring symmetry-equivalent ring1's of the molecules are inclined at 37.9 (1)° to each other (Fig. 2). The two shortest intermolecular C···O contacts are O···3ⁱⁱ and O···C4ⁱⁱ, both of these distances being 3.33 (1) Å [symmetry code: (i) -x - 0.5, y - 0.5, -z + 0.5]. These intermolecular C···O distances are quite short comparing with previously known structures containing the diphenyl ether moiety from the Cambridge Structural Database (CSD; Allen & Kennard, 1993). Another short intermolecular contact is due to ring2 packing with one parallel symmetry-equivalent copy of itself on one side together with a short Br···C interaction on the opposite side of ring2 [Br4···C11ⁱⁱⁱ=3.548 (5) Å; symmetry code: (iii) x - 1, y, z], which is the shortest intermolecular Br···C contact distance in the present strucutre.

Thus, the structure can be described as a packing of long chains held together by intermolecular interactions of the first ring between different molecules, the other ring then orders different chains to each other. Intermolecular Br···Br contacts further stabilize the structure with the shortest intermolecular Br···Br distance being Br3···Br4^iv = 3.798 (1) Å [symmetry code: (iv) x + 1, y, z]. This is not a specially short intermolecular distance compared to other bromine substituted aromatic compounds found in the CSD and significantly longer than the short Br···Br contact in phenyl 2,4,6-tribromophenyl ether (Eriksson & Hu, 2001). Thus, one can speculate that the Br···Br contacts only contribute a small part of the lattice energy.

S2. Experimental

The synthesis of the PBDE was carried out by coupling diphenyliodonium salt with a bromophenylate (Beringer et al., 1959; Ziegler & Marr, 1962; Hu, 1996, 1999). The title compound was recrystallized from methanol.

S3. Refinement

Two data sets were collected with the Stoe IPDS system (Stoe, 1997), and these were merged and scaled together. The applied scale factor was 0.989 between the two data sets.

Computing details

Data collection: EXPOSE (Stoe & Cie, 1997); cell refinement: CELL (Stoe & Cie, 1997); data reduction: INTEGRATE (Stoe & Cie, 1997) and X-RED (Stoe & Cie, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Bergerhoff, 1996).

Figures

	Fig. 1. One molecule of the title compound with the atom-numbering scheme. Displacement ellipsoids are shown at the 50% probability level. H atoms are shown as small circles of arbitrary radii.
	Fig. 2. Stereoview of the molecular packing with the close contacts between one of the two different aromatic rings (C1–C6) with symmetry equivalents.

2,4-Dibromophenyl 2,6-dibromophenyl ether

Crystal data

C12H6Br4O	F(000) = 904
Mr = 485.81	Dx = 2.331 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 8.0274 (12) Å	Cell parameters from 1520 reflections
b = 8.389 (2) Å	θ = 2.0–26.0°
c = 20.562 (3) Å	µ = 11.61 mm^−1
β = 90.606 (19)°	T = 293 K
V = 1384.5 (5) Å^3	Prism, colourless
Z = 4	0.19 × 0.13 × 0.10 mm

Data collection

Stoe IPDS diffractometer	2676 independent reflections
Radiation source: fine-focus sealed tube	1625 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.049
Detector resolution: 6.0 pixels mm^-1	θmax = 26.0°, θmin = 2.0°
area detector scans	h = −9→9
Absorption correction: numerical (X-RED; Stoe & Cie, 1998)	k = 0→10
Tmin = 0.113, Tmax = 0.307	l = 0→25
21426 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)] = 0.029	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.056	H-atom parameters constrained
S = 0.98	w = 1/[σ^2(Fo^2) + (0.01P)^2] where P = (Fo^2 + 2Fc^2)/3
2676 reflections	(Δ/σ)max = 0.001
154 parameters	Δρmax = 0.73 e Å^−3
0 restraints	Δρmin = −0.48 e Å^−3

Special details

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	0.37474 (8)	0.79973 (7)	0.49740 (3)	0.06062 (19)
Br2	0.14261 (7)	0.17691 (7)	0.44307 (3)	0.06174 (19)
Br3	0.18930 (7)	0.33100 (9)	0.24653 (3)	0.0776 (2)
Br4	−0.44275 (7)	0.46331 (9)	0.35089 (3)	0.0690 (2)
O	−0.0809 (4)	0.3541 (4)	0.34891 (15)	0.0431 (9)
C1	−0.1348 (6)	0.4031 (6)	0.2873 (2)	0.0424 (13)
C2	−0.3008 (6)	0.4525 (6)	0.2790 (2)	0.0424 (13)
C3	−0.3584 (7)	0.4959 (6)	0.2174 (2)	0.0495 (14)
H3	−0.4684	0.5283	0.2117	0.059*
C4	−0.2535 (7)	0.4912 (7)	0.1648 (3)	0.0574 (16)
H4	−0.2917	0.5212	0.1237	0.069*
C5	−0.0894 (8)	0.4411 (7)	0.1740 (3)	0.0592 (17)
H5	−0.0181	0.4366	0.1386	0.071*
C6	−0.0326 (6)	0.3988 (7)	0.2340 (3)	0.0460 (14)
C7	0.0189 (5)	0.4626 (6)	0.3829 (2)	0.0341 (11)
C8	0.0124 (7)	0.6244 (7)	0.3729 (2)	0.0467 (14)
H8	−0.0621	0.6666	0.3426	0.056*
C9	0.1154 (7)	0.7232 (6)	0.4075 (2)	0.0531 (15)
H9	0.1116	0.8326	0.4002	0.064*
C10	0.2246 (6)	0.6626 (6)	0.4529 (2)	0.0396 (12)
C11	0.2311 (6)	0.5003 (6)	0.4650 (2)	0.0383 (12)
H11	0.3030	0.4592	0.4966	0.046*
C12	0.1276 (6)	0.4006 (6)	0.4290 (2)	0.0377 (12)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0811 (4)	0.0466 (4)	0.0537 (3)	−0.0138 (3)	−0.0187 (3)	−0.0036 (3)
Br2	0.0725 (4)	0.0316 (3)	0.0806 (4)	0.0033 (3)	−0.0245 (3)	0.0053 (3)
Br3	0.0446 (3)	0.0916 (6)	0.0966 (5)	0.0041 (4)	0.0088 (3)	−0.0131 (5)
Br4	0.0505 (4)	0.1038 (6)	0.0529 (3)	0.0063 (4)	0.0068 (3)	0.0120 (4)
O	0.050 (2)	0.037 (2)	0.043 (2)	−0.0027 (17)	−0.0174 (17)	0.0038 (17)
C1	0.041 (3)	0.036 (3)	0.050 (3)	−0.007 (2)	−0.013 (3)	0.000 (3)
C2	0.044 (3)	0.043 (3)	0.040 (3)	−0.006 (3)	0.001 (2)	−0.002 (3)
C3	0.053 (3)	0.049 (4)	0.046 (3)	0.000 (3)	−0.017 (3)	0.008 (3)
C4	0.070 (4)	0.057 (4)	0.045 (3)	−0.008 (3)	−0.004 (3)	0.006 (3)
C5	0.070 (4)	0.065 (5)	0.043 (3)	−0.011 (3)	0.019 (3)	−0.007 (3)
C6	0.031 (3)	0.054 (4)	0.053 (3)	0.000 (3)	−0.002 (3)	−0.005 (3)
C7	0.031 (3)	0.041 (3)	0.031 (3)	0.000 (2)	0.000 (2)	0.000 (2)
C8	0.060 (4)	0.035 (3)	0.044 (3)	0.008 (3)	−0.015 (3)	0.000 (3)
C9	0.083 (4)	0.028 (3)	0.049 (3)	0.009 (3)	−0.013 (3)	0.003 (3)
C10	0.048 (3)	0.037 (3)	0.033 (3)	−0.004 (3)	0.003 (2)	−0.004 (2)
C11	0.042 (3)	0.038 (3)	0.035 (3)	0.005 (2)	−0.010 (2)	−0.001 (2)
C12	0.037 (3)	0.030 (3)	0.046 (3)	0.008 (2)	0.005 (2)	0.002 (2)

Geometric parameters (Å, º)

Br1—C10	1.895 (5)	C7—C8	1.373 (7)
Br2—C12	1.902 (5)	C7—C12	1.383 (6)
Br3—C6	1.885 (5)	C8—C9	1.365 (7)
Br4—C2	1.879 (5)	C9—C10	1.371 (7)
O—C7	1.395 (5)	C10—C11	1.384 (6)
O—C1	1.397 (5)	C11—C12	1.388 (6)
C1—C6	1.376 (7)	C3—H3	0.9300
C1—C2	1.404 (6)	C4—H4	0.9300
C2—C3	1.393 (6)	C5—H5	0.9300
C3—C4	1.378 (7)	C8—H8	0.9300
C4—C5	1.394 (7)	C9—H9	0.9300
C5—C6	1.358 (7)	C11—H11	0.9300
C7—O—C1	115.7 (4)	C9—C10—Br1	120.1 (4)
C6—C1—O	122.2 (4)	C11—C10—Br1	119.1 (4)
C6—C1—C2	118.9 (4)	C10—C11—C12	118.4 (4)
O—C1—C2	118.8 (4)	C11—C12—C7	120.6 (5)
C3—C2—C1	119.6 (5)	C11—C12—Br2	118.5 (4)
C3—C2—Br4	120.3 (4)	C7—C12—Br2	120.9 (4)
C1—C2—Br4	120.1 (4)	C4—C3—H3	119.8
C4—C3—C2	120.4 (5)	C2—C3—H3	119.8
C3—C4—C5	119.2 (5)	C3—C4—H4	120.4
C6—C5—C4	120.6 (5)	C5—C4—H4	120.4
C5—C6—C1	121.3 (5)	C6—C5—H5	119.7
C5—C6—Br3	120.7 (4)	C4—C5—H5	119.7
C1—C6—Br3	118.0 (4)	C9—C8—H8	120.0
C8—C7—C12	119.8 (5)	C7—C8—H8	120.0
C8—C7—O	123.3 (4)	C8—C9—H9	119.7
C12—C7—O	116.9 (5)	C10—C9—H9	119.7
C9—C8—C7	120.0 (5)	C10—C11—H11	120.8
C8—C9—C10	120.5 (5)	C12—C11—H11	120.8
C9—C10—C11	120.7 (5)
C1—O—C7—C8	26.3 (6)	C1—O—C7—C12	−154.2 (4)
C7—O—C1—C2	−104.6 (5)	C7—O—C1—C6	78.0 (6)