Crystal structure of (E)-1,2-bis­­(4-bromo-2,6-di­fluoro­phen­yl)diazene

In the crystal, mol­ecules of the centrosymmetric title compound, C₁₂H₄Br₂F₄N₂, are linked into strands along [011] by weak C—H⋯F contacts. Furthermore, the mol­ecules are π–π stacked with perpendicular ring distances of 3.4530 (9) Å.

1. Related literature

For background on azo­benzenes, see: Mitscherlich (1834); Fehrentz et al. (2011); Banghart et al. (2004); Levitz et al. (2013); Broichhagen et al. (2014); Velema et al. (2013); Bléger et al. (2012). For the synthesis, see: Bléger et al. (2012). For related structures, see: Wragg et al. (2011); Gabe et al. (1981); Crispini et al. (1998); Elder & Vargas-Baca (2012); Komeyama et al. (1973); Ferguson et al. (1998); Reichenbächer et al. (2007).

2. Experimental

2.1. Crystal data

• C₁₂H₄Br₂F₄N₂

• M_r = 411.98

• Monoclinic, P 2₁ /c

• a = 10.3274 (5) Å

• b = 4.5667 (2) Å

• c = 13.1039 (6) Å

• β = 90.340 (3)°

• V = 618.00 (5) ų

• Z = 2

• Mo Kα radiation

• μ = 6.60 mm⁻¹

• T = 173 K

• 0.14 × 0.07 × 0.02 mm

2.2. Data collection

• Bruker D8 Quest diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2012) T_min = 0.572, T_max = 0.746

• 9803 measured reflections

• 1523 independent reflections

• 1218 reflections with I > 2σ(I)

• R_int = 0.051

2.3. Refinement

• R[F² > 2σ(F²)] = 0.027

• wR(F²) = 0.055

• S = 1.02

• 1523 reflections

• 91 parameters

• H-atom parameters constrained

• Δρ_max = 0.36 e Å⁻³

• Δρ_min = −0.30 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5⋯F2^i	0.95	2.53	3.190 (3)	126
Symmetry code: (i) .

Data collection: Bruker Instrument Service (Bruker, 2007); cell refinement: APEX2 (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-III (Burnett & Johnson, 1996); software used to prepare material for publication: PLATON (Spek, 2009).

Supporting information

S1. Comment

Azobenzenes, first discovered in 1834 [Mitscherlich (1834)], are experiencing a renaissance in the last decade for the photocontrol of biological function [Fehrentz et al. (2011)]. They offer cis-/trans-isomerism upon irradiation with discrete and orthogonal wavelengths of light. When attached to a pharmacophore, this conformational change has an impact on binding affinities to its biological target. Therefore, a wide variety of transmembrane proteins, such as ion-channels [Banghart et al. (2004)] and metabotropic receptors [Levitz et al. (2013)], as well as enzymatic activity [Broichhagen et al. (2014)] and cell survival [Velema et al. (2013)] has been manipulated with azobenzene-based molecular structures. With our ongoing research in photopharmacology, we aimed to synthesize tetrafluoro-azobenzenes, which are characterized by their bistability once isomerized [Bléger et al. (2012)]. During our synthetic studies, we obtained (E)-1,2-bis(4-bromo-2,6-difluorophenyl)diazene (1) in a crystalline form, which we are reporting herein. This symmetric molecule serves as a precursor for further functionalization and implementation in photopharmacological studies, which will be described in a separate publication.

The molecular structure of the title compound is depicted in Figure 1. There are several structures containing (E)-1,2-bis(phenyl)diazene derivatives with at least one halogen substituent in 2-, 4- or 6-position reported in the literature, e.g. Wragg et al. (2011), Gabe et al. (1981), Crispini et al. (1998), Elder & Vargas-Baca (2012) and Komeyama et al. (1973). Furthermore there are two structures reported which contain the 4-bromo-2,6-difluorophenyl moiety [Ferguson et al. (1998), Reichenbächer et al. (2007)]. Due to centrosymmetry the phenyl rings are exactly coplanar, however, the entire molecule deviates significantly from exact planarity. The bond of the azo group forms an angle of 4.04 (16)° with the least-square plane of the phenyl ring while it is much larger with 13.21 (12)° in a related structure [Crispini et al. (1998)]. The C4–Br1 bond encloses an angle of 2.95 (10)° with the least-square plane of the phenyl ring which is quite close to the angle of 0.2 (3)° in a reported 4-bromo-2,6-difluorophenyl derivative [Ferguson et al. (1998)]. The 4-bromo-2,6-difluorophenyl derivative reported of Reichenbächer et al. (2007) is suitable for the comparison of bond lengths with the title compound since both compounds have been investigated at 173 K. In the title compound, the C–Br bond distance is 1.888 (2) Å which is almost in the same range of distances found in the reported structure: 1.889 (5), 1.883 (6) and 1.882 (6) Å. The C–F distances are 1.345 (3) and 1.335 (3) Å in the title compound and in the range of 1.336 (7) to 1.353 (7) Å in the related derivative [Reichenbächer et al. (2007)].

The packing of the title compound is dominated by weak C–H···F contacts, Br-π contacts and π-stacking. Strands along [011] are formed by C–H···F contacts (see Figure 2 and Table 1 for details). The π-stacking is well visible in Figure 3. The molecules are arranged staggered by what the azo group and the Br substituent of adjacent molecules are located above or below a phenyl ring. The centre of gravity of the phenyl ring (coordinates x = 0.28683, y = 0.5321, z = 0.56133) is in a distance of 3.412 and 3.459 Å from the N-atoms of the azo group (N1ⁱⁱ with ⁱⁱ = x,1 + y,z and N1ⁱⁱⁱ with ⁱⁱⁱ = 1 - x,2 - y,-z resp.) and 3.573 (1) Å from an adjacent Br substituent (Br1^iv with ^iv = x,-1 + y,z). The perpendicular distances of phenyl rings interacting by π-contacts are in a narrow range of 3.4528 (9) and 3.4532 (9) Å with a Cg–Cg distance of 4.5665 (14) Å. Besides the π contact the Br substituent forms weak contacts to two adjacent Br substituents in a distance of 3.6817 (4) Å each (Br1^v and Br1^vi with ^v = -x,1/2 + y,1/2 - z and ^vi = -x,-1/2 + y,1/2 - z).

Related literature

For background on azobenzenes, see: Mitscherlich (1834); Fehrentz et al. (2011); Banghart et al. (2004); Levitz et al. (2013); Broichhagen et al. (2014); Velema et al. (2013); Bléger et al. (2012). For the synthesis, see: Bléger et al. (2012). For related structures, see: Wragg et al. (2011); Gabe et al. (1981); Crispini et al. (1998); Elder & Vargas-Baca (2012); Komeyama et al. (1973); Ferguson et al. (1998); Reichenbächer et al. (2007).

S2. Experimental

(E)-1,2-bis(4-bromo-2,6-difluorophenyl)diazene (1) was synthesized as reported before and the spectral data matched the previously reported data [Bléger et al. (2012)]. Crystals suitable for X-Ray diffractometry were obtained as deep-red needles by slow evaporization from chloroform.

S3. Refinement

All H atoms were found in difference maps. C-bonded H atoms were positioned in ideal geometry (C—H = 0.95 Å) and treated as riding on their parent atoms [U_iso(H) = 1.2U_eq(C)].

Computing details

Data collection: Bruker Instrument Service (Bruker, 2007); cell refinement: APEX2 (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-III (Burnett & Johnson, 1996); software used to prepare material for publication: PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular structure of the title compound, with atom labels and anisotropic displacement ellipsoids (drawn at 30% probability level) for non-H atoms. Symmetry code: (i) 1 - x, 2 - y, 1 - z.
	Fig. 2. Weak C—H···F contacts (dotted lines) linking the title compound into strands along [011].
	Fig. 3. The unit cell of the title compound (displacement ellipsoids drawn at 30% probability level).

(E)-1,2-bis(4-bromo-2,6-difluorophenyl)diazene

Crystal data

C12H4Br2F4N2	F(000) = 392
Mr = 411.98	Dx = 2.214 (1) Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 95 reflections
a = 10.3274 (5) Å	θ = 5.4–24.6°
b = 4.5667 (2) Å	µ = 6.60 mm^−1
c = 13.1039 (6) Å	T = 173 K
β = 90.340 (3)°	Platelet, orange
V = 618.00 (5) Å^3	0.14 × 0.07 × 0.02 mm
Z = 2

Data collection

Bruker D8 Quest diffractometer	1523 independent reflections
Radiation source: Microfocus source, Bruker IµS	1218 reflections with I > 2σ(I)
Focusing mirrors monochromator	Rint = 0.051
Detector resolution: 10.4167 pixels mm^-1	θmax = 28.4°, θmin = 3.1°
mix of phi and ω scans	h = −13→13
Absorption correction: multi-scan (SADABS; Bruker, 2012)	k = −6→6
Tmin = 0.572, Tmax = 0.746	l = −17→17
9803 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)] = 0.027	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.055	H-atom parameters constrained
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0231P)^2 + 0.2317P] where P = (Fo^2 + 2Fc^2)/3
1523 reflections	(Δ/σ)max < 0.001
91 parameters	Δρmax = 0.36 e Å^−3
0 restraints	Δρmin = −0.30 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 > 2σ(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
C1	0.3771 (2)	0.7379 (5)	0.52174 (17)	0.0188 (5)
C2	0.2748 (2)	0.6243 (6)	0.46388 (18)	0.0232 (5)
C3	0.1860 (2)	0.4296 (6)	0.49948 (18)	0.0233 (5)
H3	0.1179	0.3594	0.4570	0.028*
C4	0.1983 (2)	0.3376 (5)	0.59963 (18)	0.0197 (5)
C5	0.2992 (2)	0.4325 (5)	0.66162 (18)	0.0216 (5)
H5	0.3084	0.3629	0.7296	0.026*
C6	0.3856 (2)	0.6304 (5)	0.62162 (18)	0.0205 (5)
N1	0.45691 (19)	0.9452 (5)	0.47266 (15)	0.0234 (4)
F1	0.26329 (15)	0.7158 (4)	0.36666 (10)	0.0382 (4)
F2	0.48197 (15)	0.7201 (4)	0.68235 (11)	0.0373 (4)
Br1	0.07408 (2)	0.08357 (6)	0.656884 (19)	0.02666 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0172 (11)	0.0184 (13)	0.0208 (12)	−0.0001 (10)	0.0014 (9)	−0.0017 (10)
C2	0.0266 (13)	0.0257 (14)	0.0173 (12)	−0.0002 (10)	−0.0020 (9)	0.0017 (10)
C3	0.0206 (12)	0.0262 (14)	0.0230 (12)	−0.0035 (11)	−0.0047 (9)	−0.0029 (12)
C4	0.0173 (12)	0.0150 (12)	0.0270 (13)	0.0020 (9)	0.0046 (9)	−0.0014 (10)
C5	0.0239 (12)	0.0215 (13)	0.0193 (11)	0.0016 (11)	−0.0011 (9)	0.0003 (11)
C6	0.0203 (12)	0.0199 (13)	0.0214 (12)	0.0000 (10)	−0.0052 (9)	−0.0049 (10)
N1	0.0221 (11)	0.0239 (11)	0.0243 (11)	−0.0046 (9)	−0.0016 (8)	0.0014 (10)
F1	0.0385 (9)	0.0555 (11)	0.0205 (8)	−0.0178 (8)	−0.0093 (6)	0.0125 (8)
F2	0.0372 (9)	0.0479 (10)	0.0268 (8)	−0.0201 (8)	−0.0142 (7)	0.0079 (8)
Br1	0.02328 (14)	0.02389 (15)	0.03287 (15)	−0.00452 (11)	0.00594 (9)	0.00056 (13)

Geometric parameters (Å, º)

C1—C2	1.397 (3)	C4—C5	1.387 (3)
C1—C6	1.400 (3)	C4—Br1	1.888 (2)
C1—N1	1.412 (3)	C5—C6	1.376 (3)
C2—F1	1.345 (3)	C5—H5	0.9500
C2—C3	1.362 (3)	C6—F2	1.335 (3)
C3—C4	1.383 (3)	N1—N1^i	1.244 (4)
C3—H3	0.9500
C2—C1—C6	114.8 (2)	C3—C4—Br1	120.30 (18)
C2—C1—N1	116.3 (2)	C5—C4—Br1	117.97 (18)
C6—C1—N1	128.9 (2)	C6—C5—C4	117.9 (2)
F1—C2—C3	118.1 (2)	C6—C5—H5	121.0
F1—C2—C1	117.5 (2)	C4—C5—H5	121.0
C3—C2—C1	124.4 (2)	F2—C6—C5	117.2 (2)
C2—C3—C4	117.7 (2)	F2—C6—C1	119.4 (2)
C2—C3—H3	121.2	C5—C6—C1	123.3 (2)
C4—C3—H3	121.2	N1^i—N1—C1	115.1 (2)
C3—C4—C5	121.7 (2)
C6—C1—C2—F1	−178.8 (2)	Br1—C4—C5—C6	−176.42 (17)
N1—C1—C2—F1	1.6 (3)	C4—C5—C6—F2	179.8 (2)
C6—C1—C2—C3	1.7 (4)	C4—C5—C6—C1	−0.5 (4)
N1—C1—C2—C3	−177.9 (2)	C2—C1—C6—F2	178.4 (2)
F1—C2—C3—C4	−179.7 (2)	N1—C1—C6—F2	−2.1 (4)
C1—C2—C3—C4	−0.2 (4)	C2—C1—C6—C5	−1.2 (4)
C2—C3—C4—C5	−1.7 (4)	N1—C1—C6—C5	178.3 (2)
C2—C3—C4—Br1	176.76 (18)	C2—C1—N1—N1^i	176.3 (3)
C3—C4—C5—C6	2.1 (4)	C6—C1—N1—N1^i	−3.2 (4)

Symmetry code: (i) −x+1, −y+2, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5···F2^ii	0.95	2.53	3.190 (3)	126

Symmetry code: (ii) −x+1, y−1/2, −z+3/2.