1,3-Bis(2,4-dibromophenyl)triazene

The crystal structure of the title compound, C₁₂H₇Br₄N₃, shows that the stereochemistry about the N=N double bond of the N=N—N(H) moiety is trans. The whole mol­ecule deviates slightly from planarity (r.m.s. deviation 0.164 Å). While one of the aryl substituents is almost coplanar with the triazene chain, weak intermolecular Br...C contacts cause the second aryl substituent to deviate by an angle of 9.1 (8)° from the plane defined by the N=N—N group. Weak intermolecular N—H...Br interactions between mol­ecules related by the diagonal glide plane give rise to chains, which are stacked along the [100] crystallographic direction. An unequal distribution of double-bond character between the N atoms suggests a delocalization of π electrons over the diazo­amino group and the adjacent aryl groups.

S1. Comment

Free 1,3-disubstituted triazenes, RN═N—N(H)R, are generally believed to adopt a trans stereochemistry about the N═N double-bond (Moore & Robinson, 1986). This arrangement has been confirmed for numerous examples characterized by X-ray diffraction. Here, we report the synthesis and structural characterization of the title compound, (I), a symmetric disubstituted 1,3-diaryltriazene having polarizable halogen atoms on the terminal aryl rings. These halogen atoms make contacts with the H atom of the protonated triazenide chain. \sch

The molecular structure of (I) is shown in Fig. 1 and selected geometric parameters are given in Table 1. Deviations from the normal N—N and C_ar—N bond lengths suggest delocalization of the π electrons on the triazene group extended to the terminal aryl substituents. N1═N2 [1.267 (7) Å] is longer than the characteristic value for a double bond (1.24 Å), whereas N2—N3 [1.332 (7) Å] is shorter than the characteristic value for a single bond (1.44 Å) (International Tables for X-Ray Crystallography, 1985, Vol. III, p. 270). Both N1—C11 [1.422 (7) Å] and N3—C31 [1.388 (8) Å] are shorter than expected for a C_ar—N single bond. These values are in good agreement with those found in related compounds (Zhang et al., 1999; Walton et al., 1991).

The terminal 2,4-dibromophenyl substituents make an interplanar angle of 14.7 (2)°, indicating the lack of planarity of the whole molecule. Due to the weak intramolecular N3—H3···Br3 interaction [N3···Br3 3.076 (5) Å], the related 2,4-dibromophenyl substituent is nearly coplanar with the N1═ N2—N3 group [N2—N3—C31—C32 174.7 (6)°].

The crystal structure of (I) reveals that diagonal glide-plane-related molecules are ordered as polymer chains by weak N3—H3···Br2 intermolecular interactions [N3···Br2ⁱ 3.717 (6) Å; symmetry code: (i) x + 1/2, 1/2 - y, z - 1/2]. These polymer chains are stacked along the [100] direction, and are associated in pairs by an inversion centre. Weak interactions between these pairs can be recognized by intermolecular C···Br contacts [C16···Br1ⁱⁱ 3.788 (7) Å; symmetry code: (ii) 2 - x, 1 - y, 2 - z]. On the other hand, weak intermolecular C···Br contacts [C13···Br3ⁱⁱⁱ 3.419 (6) Å and C14···Br3ⁱⁱⁱ 3.455 (7) Å; symmetry code: (iii) x - 1/2, 1/2 - y, 1/2 + z] observed along the individual polymer chains hinder the coplanarity of the C11—C16 aryl group with the plane defined by the N1═N2—N3 group [interplanar angle 9.1 (8)°].

S2. Experimental

2,4-Dibromoaniline (5.02 g, 20.0 mmol) was dissolved in glacial acetic acid (40 ml) and cooled below room temperature. A sodium nitrite solution (0.69 g, 10 mmol) in water (10 ml) was slowly added with continuous stirring. A yellow precipitate was observed. After complete addition of the above solution, the resulting mixture was neutralized with a 10% aqueous solution of NaHCO₃. The yellow crude product was isolated by filtration and dried over P₂O₅ under vacuum. The product was recrystallized from a tetrahydrofuran/n-hexane mixture (1:1). Yellow plate-shaped crystals of (I) suitable for X-ray analysis were obtained by slow evaporation of the solvent mixture (yield 6.35 g, 95%; m.p. 428–429 K).

S3. Refinement

H atoms were treated as riding, with C—H = 0.93 Å, N—H = 0.86 Å and U_iso(H) = 1.2U_eq of the parent atom. Are these the correct restraints?

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: SET4 in CAD-4 EXPRESS; data reduction: HELENA (Spek, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-32 (Farrugia, 1997) and PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97 and ORTEP-32.

Figures

Fig. 1. The molecular structure of (I) with 70% probability displacement ellipsoids. H atoms are shown as small spheres of arbitrary radii.

1,3-Bis(2,4-dibromophenyl)triazene

Crystal data

C12H7Br4N3	F(000) = 960
Mr = 512.85	Dx = 2.304 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71069 Å
a = 10.701 (5) Å	Cell parameters from 25 reflections
b = 9.949 (5) Å	θ = 6.2–15.1°
c = 13.888 (5) Å	µ = 10.88 mm^−1
β = 90°	T = 293 K
V = 1478.6 (11) Å^3	Plate, yellow
Z = 4	0.3 × 0.2 × 0.1 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	2045 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.037
Graphite monochromator	θmax = 26.0°, θmin = 3.2°
θ/2θ scans	h = −13→13
Absorption correction: ψ-scan (Spek, 1990)	k = −12→1
Tmin = 0.115, Tmax = 0.337	l = 0→17
3358 measured reflections	3 standard reflections every 60 min
2878 independent reflections	intensity decay: variation 0.5%

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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.111	H-atom parameters constrained
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0616P)^2] where P = (Fo^2 + 2Fc^2)/3
2878 reflections	(Δ/σ)max = 0.001
172 parameters	Δρmax = 1.01 e Å^−3
0 restraints	Δρmin = −1.00 e Å^−3

Special details

Geometry. Mean-plane data from final SHELXL refinement run:-

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

6.0726 (0.0241) x - 6.8524 (0.0199) y - 6.2773 (0.0343) z = 4.4174 (0.0279)

* -0.0005 (0.0045) C11 * 0.0006 (0.0046) C12 * 0.0037 (0.0046) C13 * -0.0081 (0.0047) C14 * 0.0080 (0.0048) C15 * -0.0038 (0.0047) C16

Rms deviation of fitted atoms = 0.0051

6.4038 (0.0317) x - 5.7985 (0.0621) y - 7.6461 (0.0976) z = 4.8162 (0.0239)

Angle to previous plane (with approximate e.s.d.) = 8.48 (0.81)

* 0.0000 (0.0000) N1 * 0.0000 (0.0000) N2 * 0.0000 (0.0000) N3

Rms deviation of fitted atoms = 0.0000

6.1338 (0.0228) x - 5.2575 (0.0219) y - 8.7085 (0.0292) z = 4.7291 (0.0091)

Angle to previous plane (with approximate e.s.d.) = 5.57 (0.85)

* 0.0034 (0.0043) C31 * -0.0096 (0.0046) C32 * 0.0080 (0.0046) C33 * -0.0004 (0.0046) C34 * -0.0057 (0.0047) C35 * 0.0043 (0.0046) C36

Rms deviation of fitted atoms = 0.0060

6.0530 (0.0142) x - 6.9156 (0.0124) y - 6.1730 (0.0103) z = 4.4060 (0.0171)

Angle to previous plane (with approximate e.s.d.) = 14.21 (0.30)

* 0.0191 (0.0030) Br1 * 0.0038 (0.0031) Br2 * -0.0086 (0.0050) C11 * -0.0166 (0.0054) C12 * -0.0094 (0.0052) C13 * -0.0076 (0.0056) C14 * 0.0179 (0.0056) C15 * 0.0015 (0.0048) C16

Rms deviation of fitted atoms = 0.0122

6.0142 (0.0138) x - 5.2511 (0.0065) y - 8.8552 (0.0169) z = 4.6711 (0.0050)

Angle to previous plane (with approximate e.s.d.) = 14.68 (0.18)

* -0.0273 (0.0030) Br3 * -0.0267 (0.0029) Br4 * 0.0019 (0.0048) C31 * 0.0105 (0.0054) C32 * 0.0385 (0.0053) C33 * 0.0190 (0.0053) C34 * -0.0079 (0.0053) C35 * -0.0080 (0.0047) C36

Rms deviation of fitted atoms = 0.0210

6.4038 (0.0317) x - 5.7985 (0.0621) y - 7.6461 (0.0976) z = 4.8162 (0.0239)

Angle to previous plane (with approximate e.s.d.) = 6.26 (0.81)

* 0.0000 (0.0000) N1 * 0.0000 (0.0000) N2 * 0.0000 (0.0000) N3

Rms deviation of fitted atoms = 0.0000

6.0530 (0.0142) x - 6.9156 (0.0124) y - 6.1730 (0.0103) z = 4.4060 (0.0171)

Angle to previous plane (with approximate e.s.d.) = 9.06 (0.76)

* 0.0191 (0.0030) Br1 * 0.0038 (0.0031) Br2 * -0.0086 (0.0050) C11 * -0.0166 (0.0054) C12 * -0.0094 (0.0052) C13 * -0.0076 (0.0056) C14 * 0.0179 (0.0056) C15 * 0.0015 (0.0048) C16

Rms deviation of fitted atoms = 0.0122

6.4038 (0.0317) x - 5.7985 (0.0621) y - 7.6461 (0.0976) z = 4.8162 (0.0239)

Angle to previous plane (with approximate e.s.d.) = 9.06 (0.76)

* 0.0000 (0.0000) N1 * 0.0000 (0.0000) N2 * 0.0000 (0.0000) N3

Rms deviation of fitted atoms = 0.0000

6.0142 (0.0138) x - 5.2511 (0.0065) y - 8.8552 (0.0169) z = 4.6711 (0.0050)

Angle to previous plane (with approximate e.s.d.) = 6.26 (0.81)

* -0.0273 (0.0030) Br3 * -0.0267 (0.0029) Br4 * 0.0019 (0.0048) C31 * 0.0105 (0.0054) C32 * 0.0385 (0.0053) C33 * 0.0190 (0.0053) C34 * -0.0079 (0.0053) C35 * -0.0080 (0.0047) C36

Rms deviation of fitted atoms = 0.0210

5.9745 (0.0251) x - 5.2365 (0.0268) y - 8.9172 (0.0161) z = 4.6544 (0.0135)

Angle to previous plane (with approximate e.s.d.) = 0.34 (1/3)

* 0.0308 (0.0012) H3 * -0.0302 (0.0016) N3 * -0.0014 (0.0041) C31 * 0.0152 (0.0038) C32 * -0.0144 (0.0018) Br3

Rms deviation of fitted atoms = 0.0215

6.4883 (0.0042) x - 5.8950 (0.0056) y - 7.3775 (0.0085) z = 4.8734 (0.0034)

Angle to previous plane (with approximate e.s.d.) = 7.90 (0.31)

* 0.4050 (0.0025) Br1 * -0.0972 (0.0028) Br2 * -0.0229 (0.0060) C11 * 0.1222 (0.0058) C12 * 0.1055 (0.0056) C13 * -0.0719 (0.0058) C14 * -0.2030 (0.0060) C15 * -0.1894 (0.0061) C16 * -0.0019 (0.0052) N1 * 0.0046 (0.0052) N2 * -0.0207 (0.0048) N3 * -0.0685 (0.0045) H3 * -0.3762 (0.0026) Br3 * 0.0694 (0.0028) Br4 * 0.0297 (0.0057) C31 * -0.1069 (0.0060) C32 * -0.0606 (0.0058) C33 * 0.0858 (0.0055) C34 * 0.2091 (0.0057) C35 * 0.1881 (0.0060) C36

Rms deviation of fitted atoms = 0.1637

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
Br3	0.47146 (7)	0.04492 (7)	−0.23083 (5)	0.0345 (2)
Br4	0.27792 (6)	−0.43594 (8)	−0.07722 (6)	0.0377 (2)
Br1	1.02540 (6)	0.31836 (8)	−0.06805 (5)	0.0340 (2)
Br2	1.23075 (7)	0.17883 (10)	0.29211 (5)	0.0455 (2)
N3	0.6699 (5)	0.0053 (6)	−0.0729 (4)	0.0258 (12)
H3	0.6679	0.0662	−0.1168	0.031*
N2	0.7566 (5)	0.0105 (6)	−0.0041 (4)	0.0251 (12)
N1	0.8307 (5)	0.1083 (5)	−0.0163 (4)	0.0255 (12)
C31	0.5827 (5)	−0.0980 (6)	−0.0739 (4)	0.0198 (13)
C32	0.4850 (6)	−0.0983 (7)	−0.1410 (4)	0.0267 (14)
C33	0.3964 (5)	−0.1995 (7)	−0.1443 (5)	0.0285 (16)
H33	0.3339	−0.1986	−0.1908	0.034*
C34	0.4023 (5)	−0.3008 (7)	−0.0780 (5)	0.0260 (15)
C35	0.4975 (6)	−0.3041 (7)	−0.0084 (5)	0.0288 (15)
H35	0.5005	−0.3732	0.0367	0.035*
C36	0.5859 (6)	−0.2044 (7)	−0.0074 (4)	0.0264 (15)
H36	0.6495	−0.2073	0.0383	0.032*
C11	0.9217 (5)	0.1192 (7)	0.0579 (4)	0.0231 (14)
C12	1.0164 (6)	0.2143 (7)	0.0455 (4)	0.0250 (14)
C13	1.1087 (6)	0.2326 (7)	0.1144 (4)	0.0281 (15)
H13	1.1720	0.2954	0.1054	0.034*
C14	1.1042 (6)	0.1554 (8)	0.1961 (4)	0.0300 (16)
C15	1.0126 (6)	0.0584 (8)	0.2108 (5)	0.0364 (18)
H15	1.0124	0.0052	0.2658	0.044*
C16	0.9225 (6)	0.0441 (7)	0.1411 (5)	0.0279 (15)
H16	0.8594	−0.0188	0.1505	0.034*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br3	0.0336 (4)	0.0362 (4)	0.0335 (4)	−0.0021 (3)	−0.0129 (3)	0.0050 (3)
Br4	0.0223 (3)	0.0322 (4)	0.0585 (5)	−0.0081 (3)	−0.0077 (3)	−0.0024 (4)
Br1	0.0283 (4)	0.0367 (4)	0.0369 (4)	−0.0100 (3)	−0.0060 (3)	0.0048 (3)
Br2	0.0261 (4)	0.0766 (6)	0.0339 (4)	0.0073 (4)	−0.0136 (3)	−0.0163 (4)
N3	0.019 (3)	0.024 (3)	0.034 (3)	−0.003 (2)	−0.009 (2)	0.003 (2)
N2	0.020 (3)	0.031 (3)	0.024 (3)	0.003 (3)	−0.006 (2)	−0.004 (2)
N1	0.022 (3)	0.024 (3)	0.031 (3)	−0.002 (2)	−0.012 (2)	−0.005 (3)
C31	0.014 (3)	0.022 (3)	0.023 (3)	−0.001 (3)	0.004 (2)	−0.007 (3)
C32	0.023 (3)	0.031 (4)	0.026 (3)	0.006 (3)	−0.003 (3)	0.000 (3)
C33	0.011 (3)	0.038 (4)	0.036 (3)	−0.001 (3)	−0.008 (3)	−0.007 (3)
C34	0.009 (3)	0.031 (4)	0.038 (3)	−0.001 (3)	0.001 (3)	−0.009 (3)
C35	0.021 (3)	0.021 (3)	0.044 (4)	0.001 (3)	−0.001 (3)	0.001 (3)
C36	0.019 (3)	0.032 (4)	0.028 (3)	0.000 (3)	−0.005 (3)	0.001 (3)
C11	0.013 (3)	0.029 (4)	0.027 (3)	0.000 (3)	−0.001 (2)	−0.005 (3)
C12	0.029 (3)	0.022 (3)	0.024 (3)	0.002 (3)	−0.001 (3)	−0.008 (3)
C13	0.016 (3)	0.037 (4)	0.031 (3)	0.001 (3)	−0.001 (3)	−0.009 (3)
C14	0.018 (3)	0.047 (4)	0.026 (3)	0.001 (3)	−0.004 (3)	−0.016 (3)
C15	0.030 (4)	0.052 (5)	0.027 (3)	0.015 (4)	−0.003 (3)	0.006 (4)
C16	0.020 (3)	0.028 (4)	0.036 (3)	−0.003 (3)	0.001 (3)	−0.002 (3)

Geometric parameters (Å, º)

Br3—C32	1.900 (7)	C35—C36	1.371 (9)
Br4—C34	1.892 (6)	C35—H35	0.9300
Br1—C12	1.890 (6)	C36—H36	0.9300
Br2—C14	1.913 (6)	C11—C16	1.376 (9)
N3—N2	1.332 (7)	C11—C12	1.397 (9)
N3—C31	1.388 (8)	C12—C13	1.386 (8)
N3—H3	0.8600	C13—C14	1.371 (9)
N2—N1	1.267 (7)	C13—Br3^i	3.419 (6)
N1—C11	1.422 (7)	C13—H13	0.9300
C31—C32	1.400 (8)	C14—C15	1.391 (10)
C31—C36	1.405 (9)	C14—Br3^i	3.455 (7)
C32—C33	1.384 (9)	C15—C16	1.373 (9)
C33—C34	1.366 (9)	C15—H15	0.9300
C33—H33	0.9300	C16—Br1^ii	3.788 (7)
C34—C35	1.404 (9)	C16—H16	0.9300
N2—N3—C31	120.2 (5)	C12—C11—N1	117.3 (6)
N2—N3—H3	119.9	C13—C12—C11	121.4 (6)
C31—N3—H3	119.9	C13—C12—Br1	117.8 (5)
N1—N2—N3	111.6 (5)	C11—C12—Br1	120.8 (4)
N2—N1—C11	112.9 (5)	C14—C13—C12	118.1 (6)
N3—C31—C32	120.7 (6)	C14—C13—Br3^i	80.0 (4)
N3—C31—C36	122.4 (5)	C12—C13—Br3^i	102.3 (4)
C32—C31—C36	116.9 (6)	C14—C13—H13	120.9
C33—C32—C31	122.3 (6)	C12—C13—H13	120.9
C33—C32—Br3	118.2 (4)	Br3^i—C13—H13	87.8
C31—C32—Br3	119.5 (5)	C13—C14—C15	122.4 (6)
C34—C33—C32	118.9 (5)	C13—C14—Br2	118.9 (5)
C34—C33—H33	120.5	C15—C14—Br2	118.7 (5)
C32—C33—H33	120.5	C13—C14—Br3^i	77.0 (4)
C33—C34—C35	121.0 (6)	C15—C14—Br3^i	105.4 (4)
C33—C34—Br4	119.8 (4)	Br2—C14—Br3^i	88.9 (2)
C35—C34—Br4	119.3 (5)	C16—C15—C14	117.6 (6)
C36—C35—C34	119.3 (6)	C16—C15—H15	121.2
C36—C35—H35	120.3	C14—C15—H15	121.2
C34—C35—H35	120.3	C15—C16—C11	122.6 (6)
C35—C36—C31	121.5 (6)	C15—C16—Br1^ii	100.6 (5)
C35—C36—H36	119.2	C11—C16—Br1^ii	107.0 (4)
C31—C36—H36	119.2	C15—C16—H16	118.7
C16—C11—C12	117.9 (5)	C11—C16—H16	118.7
C16—C11—N1	124.8 (6)	Br1^ii—C16—H16	60.2
C31—N3—N2—N1	177.7 (5)	C16—C11—C12—Br1	178.2 (5)
N3—N2—N1—C11	177.9 (5)	N1—C11—C12—Br1	−2.4 (8)
N2—N3—C31—C32	174.7 (6)	C11—C12—C13—C14	−0.6 (10)
N2—N3—C31—C36	−3.9 (9)	Br1—C12—C13—C14	−178.7 (5)
N3—C31—C32—C33	179.9 (6)	C11—C12—C13—Br3^i	−85.7 (6)
C36—C31—C32—C33	−1.4 (9)	Br1—C12—C13—Br3^i	96.2 (4)
N3—C31—C32—Br3	−0.4 (8)	C12—C13—C14—C15	1.5 (10)
C36—C31—C32—Br3	178.2 (5)	Br3^i—C13—C14—C15	100.1 (6)
C31—C32—C33—C34	1.9 (10)	C12—C13—C14—Br2	180.0 (5)
Br3—C32—C33—C34	−177.8 (5)	Br3^i—C13—C14—Br2	−81.4 (4)
C32—C33—C34—C35	−1.0 (10)	C12—C13—C14—Br3^i	−98.6 (6)
C32—C33—C34—Br4	177.1 (5)	C13—C14—C15—C16	−1.9 (10)
C33—C34—C35—C36	−0.3 (10)	Br2—C14—C15—C16	179.6 (5)
Br4—C34—C35—C36	−178.4 (5)	Br3^i—C14—C15—C16	82.3 (6)
C34—C35—C36—C31	0.8 (10)	C14—C15—C16—C11	1.5 (10)
N3—C31—C36—C35	178.7 (6)	C14—C15—C16—Br1^ii	119.7 (6)
C32—C31—C36—C35	0.1 (9)	C12—C11—C16—C15	−0.7 (10)
N2—N1—C11—C16	−7.8 (9)	N1—C11—C16—C15	−180.0 (6)
N2—N1—C11—C12	172.9 (6)	C12—C11—C16—Br1^ii	−115.8 (5)
C16—C11—C12—C13	0.3 (10)	N1—C11—C16—Br1^ii	64.9 (7)
N1—C11—C12—C13	179.6 (6)	N2—N3—C31—C32	174.7 (6)

Symmetry codes: (i) x+1/2, −y+1/2, z+1/2; (ii) −x+2, −y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3···Br2^iii	0.86	2.91	3.717 (6)	156
N3—H3···Br3	0.86	2.64	3.076 (5)	113

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