4,4'-Dibromo-2,2',3,3',5,5',6,6'-octafluorobiphenyl

The mol­ecule of the title compound, C₁₂Br₂F₈, shows approximate D₂ symmetry. The dihedral angle formed by the two rings is 60.2 (1)°.

S1. Comment

Our earlier work on the halogen bond shows that I···O and especially I···N interactions are strong and can successfully be used in supramolecular assembly (Cardillo et al., 2000). We expect that highly polarisable Br atoms bonded to an electron-poor aromatic ring, as in the commercially available title compound, (I), would be used as building blocks for supramolecular assembly, notwithstanding that Br···N/O interactions are weaker than the corresponding I···N/O halogen bonds. We decided to study (I) in order to have a yardstick for evaluating the effect of supramolecular assembly involving such a compound. \sch

The molecule of (I) crystallizes in a general position but presents approximate D₂ symmetry, with a molecular r.m.s. of 0.0277 (units?) (Pilati & Forni, 1999, 2000). Bond distances and angles are in the normal ranges [C—Br 1.872 (3) and 1.876 (3) Å, C—F 1.334 (4)–1.344 (4) Å, and aromatic C—C 1.370 (4)–1.386 (4) Å]. The length of the C—C bond between the rings is 1.483 (4) Å.

The main feature of biphenyl derivatives is the dihedral angle between the two rings. These molecules reach a compromise between the conjugation of π-orbitals of the aromatic system and the repulsion between the transannular ortho-bonded atoms. In (I), the contacts between the substituents at the 2- and 6-positions, F1···F5 and F4···F8, are 2.884 (4) and 2.881 (3) Å, respectively, with a dihedral angle between the phenyl rings of 60.2 (1)°; such values are identical (within one s.u.) to those found in perfluorobiphenyl (Gleason & Britton, 1976). This dihedral angle is sometimes smaller in other similar compounds; for example, the same perfluorobiphenyl, when co-crystallized with biphenyl (Naae, 1979), presents an angle of 50.5°. These values are much larger and show less spread than those found for 2,2',6,6'-unsubstituted biphenyls; for example, in the previously cited work of Naae (1979), biphenyl shows a dihedral angle of 36.4°, while in p-terphenyl (Hori & Nishiura, 1996), the same angle is near 0°.

The packing of (I) is characterized by a pair of molecules linked through a centre of symmetry; rings C1—C6 and C1ⁱ—C6ⁱ [symmetry code: (i) -x, -y, 1 - z] are placed in such a way that there is a significant interaction between the π orbital of the C5—C6 bond and Br1ⁱ, with C···Br distances of 3.598 (4) and 3.699 (4) Å. The molecular minimum-inertia axes are parallel or, if related by a screw axis or a glide plane, nearly parallel. The molecules show a head-to-tail Br2···Br1ⁱⁱ contact [symmetry code: (ii) x, y, 1 + z] of 3.654 (1) Å, with Br···Br—C angles of 134.2 (1) and 136.0 (1)°.

S2. Experimental

Compound (I) was obtained as a commercial product ex Aldrich. Suitable crystals of (I) were obtained from solution in acetone.

Computing details

Data collection: XSCANS (Siemens, 1991); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97 and PARST (Nardelli, 1983).

Figures

Fig. 1. The molecular structure of (I) with the atom-numbering scheme, showing 50% probability displacement ellipsoids.

4,4'-Dibromo-2,2',3,3',5,5',6,6'-octafluorobiphenyl

Crystal data

C12Br2F8	F(000) = 856
Mr = 455.94	Dx = 2.324 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71069 Å
a = 13.5489 (13) Å	Cell parameters from 40 reflections
b = 7.4975 (10) Å	θ = 5.4–12.9°
c = 13.6783 (12) Å	µ = 6.31 mm^−1
β = 110.309 (8)°	T = 291 K
V = 1303.1 (2) Å^3	Wedge, colourless
Z = 4	0.32 × 0.20 × 0.16 mm

Data collection

Siemens P4 diffractometer	1594 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.042
Graphite monochromator	θmax = 27.5°, θmin = 2.6°
2θ/ω scans	h = 0→17
Absorption correction: ψ-scan (North et al., 1968)	k = −9→9
Tmin = 0.253, Tmax = 0.364	l = −17→16
5995 measured reflections	3 standard reflections every 197 reflections
2993 independent reflections	intensity decay: 0.0%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0237P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.034	(Δ/σ)max = 0.002
wR(F^2) = 0.063	Δρmax = 0.32 e Å^−3
S = 0.83	Δρmin = −0.37 e Å^−3
2993 reflections	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
200 parameters	Extinction coefficient: 0.0015 (3)
0 restraints

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	0.00808 (4)	0.25356 (6)	0.38037 (3)	0.07479 (17)
Br2	0.16165 (4)	0.33724 (6)	1.21201 (3)	0.07808 (17)
F1	0.24482 (16)	0.4064 (3)	0.75691 (15)	0.0819 (7)
F2	0.20354 (17)	0.3901 (3)	0.55120 (15)	0.0882 (7)
F3	−0.13140 (16)	0.1556 (3)	0.50474 (14)	0.0815 (7)
F4	−0.09114 (15)	0.1777 (3)	0.70977 (14)	0.0722 (6)
F5	0.12490 (19)	0.6121 (2)	0.85467 (14)	0.0769 (6)
F6	0.1591 (2)	0.6334 (3)	1.05885 (15)	0.0901 (7)
F7	0.11549 (17)	0.0120 (3)	1.07033 (14)	0.0738 (6)
F8	0.07749 (16)	−0.0078 (2)	0.86526 (14)	0.0644 (5)
C1	0.0785 (3)	0.2903 (4)	0.7403 (2)	0.0444 (8)
C2	0.1509 (3)	0.3435 (5)	0.6956 (2)	0.0526 (9)
C3	0.1308 (3)	0.3344 (5)	0.5899 (2)	0.0543 (9)
C4	0.0362 (3)	0.2704 (4)	0.5244 (2)	0.0500 (9)
C5	−0.0381 (3)	0.2171 (5)	0.5662 (2)	0.0551 (9)
C6	−0.0164 (3)	0.2291 (5)	0.6720 (2)	0.0500 (9)
C7	0.0998 (2)	0.3022 (4)	0.8540 (2)	0.0450 (8)
C8	0.1222 (3)	0.4616 (4)	0.9070 (2)	0.0511 (9)
C9	0.1399 (3)	0.4735 (5)	1.0123 (2)	0.0563 (10)
C10	0.1378 (3)	0.3231 (5)	1.0689 (2)	0.0523 (9)
C11	0.1169 (3)	0.1623 (5)	1.0177 (2)	0.0495 (8)
C12	0.0976 (3)	0.1520 (4)	0.9122 (2)	0.0470 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.1068 (4)	0.0737 (3)	0.04339 (19)	0.0117 (2)	0.0255 (2)	0.00436 (19)
Br2	0.0805 (3)	0.1114 (4)	0.04391 (19)	0.0016 (3)	0.02354 (19)	−0.0027 (2)
F1	0.0520 (13)	0.1236 (18)	0.0630 (11)	−0.0243 (13)	0.0110 (10)	0.0025 (12)
F2	0.0689 (15)	0.134 (2)	0.0734 (13)	−0.0079 (14)	0.0395 (12)	0.0194 (13)
F3	0.0609 (14)	0.1106 (18)	0.0569 (11)	−0.0268 (13)	0.0000 (10)	−0.0056 (12)
F4	0.0522 (13)	0.1052 (17)	0.0623 (11)	−0.0198 (12)	0.0238 (10)	−0.0016 (11)
F5	0.1178 (18)	0.0475 (12)	0.0552 (10)	−0.0099 (12)	0.0171 (11)	0.0078 (10)
F6	0.136 (2)	0.0627 (14)	0.0615 (12)	−0.0104 (14)	0.0222 (13)	−0.0185 (11)
F7	0.0912 (16)	0.0679 (14)	0.0626 (11)	−0.0008 (12)	0.0272 (11)	0.0198 (11)
F8	0.0840 (15)	0.0437 (11)	0.0657 (11)	−0.0028 (11)	0.0261 (11)	−0.0030 (10)
C1	0.043 (2)	0.044 (2)	0.0436 (16)	0.0021 (16)	0.0115 (16)	0.0034 (14)
C2	0.033 (2)	0.065 (2)	0.0549 (19)	−0.0044 (18)	0.0088 (17)	0.0025 (18)
C3	0.049 (2)	0.069 (2)	0.0508 (18)	0.004 (2)	0.0252 (18)	0.0115 (18)
C4	0.062 (3)	0.043 (2)	0.0448 (17)	0.0098 (18)	0.0193 (18)	0.0043 (15)
C5	0.047 (2)	0.065 (3)	0.0454 (17)	−0.0050 (19)	0.0052 (17)	−0.0004 (16)
C6	0.038 (2)	0.060 (2)	0.0529 (18)	−0.0037 (17)	0.0167 (17)	0.0008 (17)
C7	0.047 (2)	0.044 (2)	0.0411 (16)	0.0004 (16)	0.0117 (15)	−0.0014 (14)
C8	0.058 (2)	0.044 (2)	0.0457 (17)	−0.0008 (18)	0.0100 (16)	0.0085 (16)
C9	0.062 (2)	0.053 (2)	0.0472 (18)	0.0009 (19)	0.0100 (18)	−0.0068 (18)
C10	0.045 (2)	0.071 (2)	0.0398 (16)	0.0047 (19)	0.0123 (15)	0.0024 (18)
C11	0.048 (2)	0.052 (2)	0.0507 (17)	0.0032 (18)	0.0192 (16)	0.0127 (19)
C12	0.047 (2)	0.046 (2)	0.0492 (17)	0.0041 (17)	0.0187 (15)	0.0042 (17)

Geometric parameters (Å, º)

Br1—C4	1.876 (3)	C1—C7	1.483 (4)
Br2—C10	1.872 (3)	C2—C3	1.377 (4)
F1—C2	1.343 (3)	C3—C4	1.370 (4)
F2—C3	1.337 (4)	C4—C5	1.380 (5)
F3—C5	1.334 (4)	C5—C6	1.376 (4)
F4—C6	1.343 (4)	C7—C8	1.377 (4)
F5—C8	1.344 (3)	C7—C12	1.386 (4)
F6—C9	1.340 (4)	C8—C9	1.378 (4)
F7—C11	1.341 (3)	C9—C10	1.374 (4)
F8—C12	1.342 (4)	C10—C11	1.373 (4)
C1—C6	1.379 (4)	C11—C12	1.376 (4)
C1—C2	1.382 (4)
C6—C1—C2	115.8 (3)	C8—C7—C12	116.5 (3)
C6—C1—C7	121.8 (3)	C8—C7—C1	122.2 (3)
C2—C1—C7	122.4 (3)	C12—C7—C1	121.3 (3)
F1—C2—C3	118.1 (3)	F5—C8—C7	119.3 (3)
F1—C2—C1	119.3 (3)	F5—C8—C9	118.4 (3)
C3—C2—C1	122.5 (3)	C7—C8—C9	122.2 (3)
F2—C3—C4	120.0 (3)	F6—C9—C10	120.3 (3)
F2—C3—C2	119.7 (3)	F6—C9—C8	119.2 (3)
C4—C3—C2	120.2 (3)	C10—C9—C8	120.4 (3)
C3—C4—C5	118.8 (3)	C11—C10—C9	118.2 (3)
C3—C4—Br1	120.9 (3)	C11—C10—Br2	120.9 (3)
C5—C4—Br1	120.3 (3)	C9—C10—Br2	120.9 (3)
F3—C5—C6	119.7 (3)	F7—C11—C10	120.2 (3)
F3—C5—C4	120.5 (3)	F7—C11—C12	118.8 (3)
C6—C5—C4	119.8 (3)	C10—C11—C12	121.0 (3)
F4—C6—C5	118.1 (3)	F8—C12—C11	119.0 (3)
F4—C6—C1	119.1 (3)	F8—C12—C7	119.4 (3)
C5—C6—C1	122.9 (3)	C11—C12—C7	121.5 (3)
C6—C1—C2—F1	179.3 (3)	C6—C1—C7—C12	60.7 (4)
C7—C1—C2—F1	0.9 (5)	C2—C1—C7—C12	−121.0 (4)
C6—C1—C2—C3	−0.8 (5)	C12—C7—C8—F5	−179.6 (3)
C7—C1—C2—C3	−179.3 (3)	C1—C7—C8—F5	0.1 (5)
F1—C2—C3—F2	−1.0 (5)	C12—C7—C8—C9	−1.1 (5)
C1—C2—C3—F2	179.1 (3)	C1—C7—C8—C9	178.6 (3)
F1—C2—C3—C4	179.7 (3)	F5—C8—C9—F6	−0.1 (5)
C1—C2—C3—C4	−0.1 (6)	C7—C8—C9—F6	−178.6 (3)
F2—C3—C4—C5	−178.7 (3)	F5—C8—C9—C10	179.9 (3)
C2—C3—C4—C5	0.5 (5)	C7—C8—C9—C10	1.4 (6)
F2—C3—C4—Br1	1.7 (5)	F6—C9—C10—C11	179.5 (3)
C2—C3—C4—Br1	−179.1 (3)	C8—C9—C10—C11	−0.5 (5)
C3—C4—C5—F3	179.4 (3)	F6—C9—C10—Br2	0.0 (5)
Br1—C4—C5—F3	−1.0 (5)	C8—C9—C10—Br2	180.0 (3)
C3—C4—C5—C6	0.1 (5)	C9—C10—C11—F7	179.2 (3)
Br1—C4—C5—C6	179.6 (3)	Br2—C10—C11—F7	−1.4 (5)
F3—C5—C6—F4	0.0 (5)	C9—C10—C11—C12	−0.6 (5)
C4—C5—C6—F4	179.3 (3)	Br2—C10—C11—C12	178.9 (3)
F3—C5—C6—C1	179.6 (3)	F7—C11—C12—F8	0.3 (5)
C4—C5—C6—C1	−1.1 (5)	C10—C11—C12—F8	−180.0 (3)
C2—C1—C6—F4	−179.0 (3)	F7—C11—C12—C7	−178.8 (3)
C7—C1—C6—F4	−0.5 (5)	C10—C11—C12—C7	0.9 (5)
C2—C1—C6—C5	1.4 (5)	C8—C7—C12—F8	−179.2 (3)
C7—C1—C6—C5	179.9 (3)	C1—C7—C12—F8	1.2 (5)
C6—C1—C7—C8	−118.9 (4)	C8—C7—C12—C11	−0.1 (5)
C2—C1—C7—C8	59.4 (5)	C1—C7—C12—C11	−179.7 (3)