2,2′-Di­iodo­azo­benzene

The mol­ecular structure of the title compound, C₁₂H₈I₂N₂ [systematic name: (E)-bis­(2-iodo­phen­yl)diazene], exhibits an essentially planar trans geometry [maximum deviation = 0.022 (4) Å] with the iodine atoms ortho to the azo bridge. In the crystal, offset π-stacking leads to the formation of columns along the a axis [closest C⋯C distance = 3.383 (4) Å].

Related literature

For analogous 2,2′-dichloro­azobenzenes, see: Komeyama et al. (1973); Crispini et al. (1998). For the structure of a related o-halogenated azobenzene, see: Wragg et al. (2011).

Experimental

Crystal data

• C₁₂H₈I₂N₂

• M_r = 433.88

• Monoclinic, P 2₁ /c

• a = 4.6306 (3) Å

• b = 18.1105 (12) Å

• c = 15.3748 (10) Å

• β = 98.532 (1)°

• V = 1275.10 (14) ų

• Z = 4

• Mo Kα radiation

• μ = 4.91 mm⁻¹

• T = 296 K

• 0.63 × 0.09 × 0.04 mm

Data collection

• Bruker SMART CCD area-detector diffractometer

• Absorption correction: analytical (SADABS; Sheldrick, 1996) T_min = 0.322, T_max = 0.873

• 16726 measured reflections

• 3186 independent reflections

• 2536 reflections with I > 2σ(I)

• R_int = 0.027

Refinement

• R[F² > 2σ(F²)] = 0.027

• wR(F²) = 0.059

• S = 1.03

• 3186 reflections

• 145 parameters

• H-atom parameters constrained

• Δρ_max = 0.56 e Å⁻³

• Δρ_min = −0.56 e Å⁻³

Data collection: SMART (Bruker, 2000); cell refinement: SMART (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXTL.

Supporting information

S1. Comment

The molecules of 2,2'-diiodoazobenzene exhibit a trans geometry with the iodine atoms in positions ortho to the azo bridge and opposite the N═N double bond (Fig. 1). The molecules are nearly planar, with the maximum deviation from the average plane being 0.022 (4) Å for atom I1. The aromatic rings of 2,2'-diiodoazobenzene are nearly co-planar with each other (interplanar angle = 0.08 (3)°) and with the azo bridge (N1—N2—C7—C12 = 0.5 (4)°; N2—N1—C1—C6 = -0.1 (4)°). These features are also observed in the structure of 2-iodoazobenzene (Wragg et al., 2011). In contrast, the structures of dichloro analogues display parallel aromatic rings that are rotated from the plane of the azo bridge with N—N—C—C angles = 14.30 (6)° and -14.30 (6)° (Komeyama et al., 1973), and 14.4 (3)° and -14.4 (1)° (Crispini et al., 1998); the corresponding interplanar distances are 0.173 (1) and 0.351 (3) Å, respectively. Such structural differences are likely linked to the presence of intermolecular contacts in the structures of the iodo derivatives and their absence in the dichloro compounds. An offset π-stacking pattern (Fig. 2) allows significant overlap of adjacent molecules. The shortest intermolecular contact in 2,2'-diiodoazobenzene is between C1 and C7* (3.383 (4) Å, cf. sum of van der Waals radii = 3.40 Å; symmetry operation: 1+x, y, z). The stacking leads a columnar arrangement along a (Fig. 3). A herringbone pattern is observed perpendicular to the c axis (Fig. 4).

Related literature

For analogous 2,2'-dichloroazobenzenes, see: Komeyama et al. (1973); Crispini et al. (1998). For the structure of a related o-halogenated azobenzene, see: Wragg et al. (2011).

S2. Experimental

Azobenzene (0.184 g, 1.01 mmol) and mercury trifluoroacetate (0.43 g, 1.01 mmol) were combined with freshly distilled trifluoroacetic acid (0.13 mL) under a nitrogen atmosphere. The mixture was heated with stirring for 4 h at 68 °C, after which a concentrated solution of sodium chloride (0.345 g, 5.90 mmol) and sodium acetate (2.085 g, 14.7 mmol) was added and the entire sample was placed in an ultrasonic bath for 20 min. After decanting the solvent, a mixture of iodine (0.279 g, 1.10 mmol) in methanol was added. With time, orange crystals of 2,2'-diiodoazobenzene grew from the solution and were collected by filtration. Yield = 0.047 g, 10%.

S3. Refinement

Carbon-bound H-atoms were placed in calculated positions (C–H 0.93 Å) and were included in the refinement in the riding model approximation with U_iso(H) set to 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. Perspective view of the crystal structure of 2,2'-diiodoazobenzene. Atoms are represented by their anisotropic displacement ellipsoids at 50% probability level. Hydrogen atoms are displayed as fixed-size spheres of 0.35 Å radius.
	Fig. 2. Intermolecular C1—C7* contacts (- - -) in the crystal of 2,2'-diiodoazobenzene. Hydrogen atoms are omitted for clarity.
	Fig. 3. Packing diagram of 2,2'-diiodoazobenzene viewed along the a axis. Hydrogen atoms are omitted for clarity.
	Fig. 4. Packing diagram of 2,2'-diiodoazobenzene viewed along the c axis. Hydrogen atoms are omitted for clarity.

(E)-bis(2-iodophenyl)diazene

Crystal data

C12H8I2N2	F(000) = 800
Mr = 433.88	Dx = 2.261 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 4767 reflections
a = 4.6306 (3) Å	θ = 2.6–24.6°
b = 18.1105 (12) Å	µ = 4.91 mm^−1
c = 15.3748 (10) Å	T = 296 K
β = 98.532 (1)°	Rod, orange
V = 1275.10 (14) Å^3	0.63 × 0.09 × 0.04 mm
Z = 4

Data collection

Bruker SMART CCD area-detector diffractometer	3186 independent reflections
Radiation source: fine-focus sealed tube	2536 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
ϕ and ω scans	θmax = 28.4°, θmin = 2.3°
Absorption correction: analytical (SADABS; Sheldrick, 1996)	h = −4→6
Tmin = 0.322, Tmax = 0.873	k = −24→22
16726 measured reflections	l = −20→18

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) = 0.059	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0243P)^2 + 0.9205P] where P = (Fo^2 + 2Fc^2)/3
3186 reflections	(Δ/σ)max = 0.001
145 parameters	Δρmax = 0.56 e Å^−3
0 restraints	Δρmin = −0.56 e Å^−3

Special details

Experimental. Azobenzene (0.184 g, 1.01 mmol) and mercury trifluoroacetate (0.43 g, 1.01 mmol) were combined with freshly distilled trifluoroacetic acid (0.13 mL) under a nitrogen atmosphere. The mixture was heated with stirring during 4 h at 68°C, after which a concentrated solution of sodium chloride (0.345 g, 5.90 mmol) and sodium acetate (2.085 g, 14.7 mmol) was added and the entire sample was placed in an ultrasonic bath for 20 min. After decanting the solvent, a mixture of iodine (0.279 g, 1.10 mmol) in methanol was added. With time, crystals of 2,2'-diiodoazobenzene grew from the solution and were collected by filtration. Yield = 0.047 g, 10%.

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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	1.0033 (6)	0.62044 (15)	0.74337 (19)	0.0362 (6)
C2	1.1608 (6)	0.67355 (16)	0.7950 (2)	0.0391 (6)
C3	1.3471 (7)	0.72094 (17)	0.7587 (2)	0.0469 (7)
C4	1.3732 (7)	0.71515 (18)	0.6711 (2)	0.0511 (8)
C5	1.2147 (7)	0.66291 (18)	0.6191 (2)	0.0447 (7)
C6	1.0330 (7)	0.61521 (17)	0.6548 (2)	0.0440 (7)
I1	1.12360 (6)	0.685129 (15)	0.927841 (16)	0.06511 (10)
H1	1.4537	0.7564	0.7936	0.056*
H2	1.4983	0.7466	0.6468	0.061*
H3	1.2306	0.6599	0.5596	0.054*
H4	0.9297	0.5794	0.6196	0.053*
N1	0.8151 (5)	0.57362 (13)	0.78379 (16)	0.0409 (6)
N2	0.6804 (5)	0.52810 (14)	0.73326 (16)	0.0400 (5)
C7	0.4922 (6)	0.48055 (16)	0.77216 (18)	0.0366 (6)
C8	0.3371 (6)	0.42818 (16)	0.71848 (19)	0.0380 (6)
C9	0.1496 (6)	0.37976 (17)	0.7525 (2)	0.0451 (7)
C10	0.1187 (7)	0.38397 (18)	0.8396 (2)	0.0511 (8)
C11	0.2731 (7)	0.43536 (19)	0.8935 (2)	0.0494 (8)
C12	0.4562 (7)	0.48416 (18)	0.8602 (2)	0.0480 (8)
I2	0.37973 (5)	0.421268 (15)	0.585578 (15)	0.06002 (9)
H5	0.0457	0.3447	0.7163	0.054*
H6	−0.0076	0.3518	0.8624	0.061*
H7	0.2537	0.4371	0.9528	0.059*
H8	0.5561	0.5196	0.8967	0.058*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0328 (14)	0.0323 (15)	0.0429 (16)	0.0017 (12)	0.0041 (12)	0.0035 (12)
C2	0.0373 (15)	0.0366 (16)	0.0435 (16)	0.0024 (12)	0.0062 (12)	−0.0016 (12)
C3	0.0422 (17)	0.0358 (17)	0.063 (2)	−0.0028 (13)	0.0096 (15)	0.0017 (14)
C4	0.0454 (18)	0.0444 (19)	0.067 (2)	0.0018 (15)	0.0191 (16)	0.0139 (16)
C5	0.0493 (18)	0.0481 (18)	0.0387 (16)	0.0036 (14)	0.0138 (14)	0.0088 (13)
C6	0.0478 (17)	0.0414 (18)	0.0429 (17)	−0.0018 (14)	0.0063 (14)	−0.0012 (13)
I1	0.07890 (19)	0.07058 (18)	0.04761 (14)	−0.02011 (13)	0.01516 (12)	−0.01476 (11)
N1	0.0414 (13)	0.0395 (14)	0.0417 (14)	−0.0054 (11)	0.0055 (11)	0.0003 (11)
N2	0.0386 (13)	0.0388 (14)	0.0420 (13)	−0.0048 (11)	0.0040 (11)	0.0009 (11)
C7	0.0339 (14)	0.0373 (16)	0.0384 (15)	0.0009 (12)	0.0045 (12)	0.0029 (12)
C8	0.0377 (15)	0.0369 (16)	0.0393 (15)	0.0032 (12)	0.0051 (12)	0.0028 (12)
C9	0.0412 (16)	0.0395 (17)	0.0541 (19)	−0.0053 (13)	0.0050 (14)	−0.0001 (14)
C10	0.0509 (19)	0.049 (2)	0.056 (2)	−0.0044 (15)	0.0161 (16)	0.0109 (16)
C11	0.059 (2)	0.055 (2)	0.0338 (15)	−0.0093 (16)	0.0077 (14)	0.0050 (14)
C12	0.0529 (19)	0.0504 (19)	0.0393 (16)	−0.0092 (15)	0.0030 (14)	−0.0020 (14)
I2	0.07077 (17)	0.06949 (17)	0.04103 (13)	−0.01261 (12)	0.01232 (11)	−0.01094 (10)

Geometric parameters (Å, º)

C1—C2	1.384 (4)	N2—C7	1.419 (3)
C2—C3	1.391 (4)	C7—C8	1.386 (4)
C3—C4	1.374 (5)	C8—C9	1.390 (4)
C4—C5	1.378 (5)	C9—C10	1.370 (4)
C5—C6	1.375 (4)	C10—C11	1.374 (5)
C6—C1	1.393 (4)	C11—C12	1.374 (4)
C2—I1	2.085 (3)	C12—C7	1.390 (4)
C3—H1	0.9300	C8—I2	2.086 (3)
C4—H2	0.9300	C9—H5	0.9300
C5—H3	0.9300	C10—H6	0.9300
C6—H4	0.9300	C11—H7	0.9300
C1—N1	1.423 (3)	C12—H8	0.9300
N1—N2	1.236 (3)
C1—C2—C3	120.3 (3)	N1—N2—C7	115.1 (2)
C2—C3—C4	119.7 (3)	C7—C8—C9	120.3 (3)
C3—C4—C5	120.3 (3)	C8—C9—C10	119.6 (3)
C4—C5—C6	120.3 (3)	C9—C10—C11	120.4 (3)
C5—C6—C1	120.1 (3)	C10—C11—C12	120.4 (3)
C6—C1—C2	119.2 (3)	C11—C12—C7	120.1 (3)
C1—C2—I1	121.2 (2)	C12—C7—N2	123.5 (3)
C3—C2—I1	118.5 (2)	C8—C7—C12	119.1 (3)
C2—C3—H1	120.1	C8—C7—N2	117.4 (2)
C4—C3—H1	120.1	C7—C8—I2	120.6 (2)
C3—C4—H2	119.9	C9—C8—I2	119.1 (2)
C5—C4—H2	119.9	C8—C9—H5	120.2
C4—C5—H3	119.8	C10—C9—H5	120.2
C6—C5—H3	119.8	C9—C10—H6	119.8
C5—C6—H4	119.9	C11—C10—H6	119.8
C1—C6—H4	119.9	C10—C11—H7	119.8
C6—C1—N1	122.8 (3)	C12—C11—H7	119.8
C2—C1—N1	117.9 (3)	C11—C12—H8	119.9
C1—N1—N2	114.0 (2)	C7—C12—H8	119.9