Anomalous halogen bonds in the crystal structures of 1,2,3-tri­bromo-5-nitro­benzene and 1,3-di­bromo-2-iodo-5-nitro­benzene

Two halogenated nitro­benzene derivatives have been characterized. The substitution of a Br substituent by an I atom modifies the network of halogen bonds, and gives rise to the formation of non-classical Br^δ+⋯I^δ- bonds.

Abstract

The title trihalogenated nitro­benzene derivatives, C₆H₂Br₃NO₂ and C₆H₂Br₂INO₂, crystallize in triclinic and monoclinic cells, respectively, with two mol­ecules per asymmetric unit in each case. The asymmetric unit of the tri­bromo compound features a polarized Br^δ+⋯Br^δ- inter­molecular halogen bond. After substitution of the Br atom in the para position with respect to the nitro group, the network of X⋯X halogen contacts is reorganized. Two inter­molecular polarized halogen bonds are then observed, which present the uncommon polarization Br^δ+⋯I^δ-: the more electronegative site (Br) behaves as a donor and the less electronegative site (I) as an acceptor for the charge transfer.

Chemical context  

Within the large class of non-covalent inter­actions studied in chemical crystallography, halogen bonds are of special inter­est in crystal engineering. The stabilizing inter­action between a halogen atom and a Lewis base, X⋯B, shares many aspects with classical hydrogen bonds, but is more directional. On the other hand, halogen contacts X⋯X are more difficult to conceptualize (Wang et al., 2014 ▸), for instance because the charge transfer in the Br⋯Br contact is not as obvious as in hydrogen bonds. Evidence supporting the importance of this topic is the recent organization of an inter­national meeting dedicated to halogen bonding (Erdelyi, 2014 ▸).

In this context, we are engaged in the synthesis and structural characterization of a series of halogen-substituted nitro­benzenes. The present communication describes two closely related compounds in the series, which differ only by the halogen atom substituting at the ring position para to the nitro group. Despite the small chemical modification, the resulting crystal structures are very different, as a consequence of a different network of halogen bonds.

Structural commentary  

Both compounds crystallize with two mol­ecules in the asymmetric unit, but in different space groups. The tri­bromo derivative, (I, Fig. 1 ▸), is a P crystal isomorphous to the chloro analogue (Bhar et al., 1995 ▸), although the unit-cell parameters are significantly larger for (I) compared to the chloro compound: the cell volume is increased by more than 7%. In the present work, we retained the Niggli reduced triclinic cell (a < b < c), while Bhar et al. used a non-reduced cell. Moreover, the asymmetric unit content was defined in order to emphasize the strongest Br⋯Br bond in (I). The bromo-iodo derivative (II, Fig. 2 ▸) crystallizes in the monoclinic system and, in that case, the standard setting was used for space group P2₁/c.

Figure 1.

The asymmetric unit of (I), with displacement ellipsoids at the 30% probability level. The dashed bond connecting the independent mol­ecules is a type-II halogen bond.

Figure 2.

The asymmetric unit of (II), with displacement ellipsoids at the 30% probability level. The dashed bonds connecting the independent mol­ecules are halogen contacts.

The C—halogen bond lengths are as expected. In (I), C—Br distances are in the range 1.821 (12)–1.886 (11) Å, slightly shorter than C—Br bond lengths observed in hexa­bromo­benzene, 1.881 Å (T = 100 K; Reddy et al., 2006 ▸) or 1.871 Å (synchrotron study, T = 100 K; Brezgunova et al., 2012 ▸). In (II), C—Br bond lengths are longer, 1.875 (13) to 1.895 (14) Å, while the C—I bond lengths, 2.088 (12) and 2.074 (14) Å, may be compared to bonds in hexa­iodo­benzene, 2.109 Å (T = 100 K; Ghosh et al., 2007 ▸) or 1,2,3-tri­iodo­benzene, 2.090 Å (T = 223 K, Novak & Li, 2007 ▸). Indeed, differences in bond lengths between perhalogenated and trihalogenated derivatives are within experimental errors, and the substitution of the 5-position by the nitro electron-withdrawing group in (I) and (II) has probably little influence on these bonds.

The important feature in these halogenated mol­ecules is rather the possibility of steric repulsion between vicinal halogen atoms, which is related to the reduction of endocyclic angles. Regarding this point, it is worth reading the Acta E article about 1,2,3-tri­iodo­benzene (Novak & Li, 2007 ▸). As in polyiodo derivatives, intra­molecular steric crowding between the halogen atoms in (I) and (II) is offset by benzene ring distortion. As a consequence, the C1—C2—C3 and equivalent C11—C12—C13 angles are systematically less than 120°: 116.2 (11) and 118.8 (13)° in (I); 118.1 (12) and 117.3 (13)° in (II). Again, the nitro group has little influence on intra­molecular halogen⋯halogen contacts. For instance, in 1,3-di­bromo-2-iodo­benzene, the C1—C2—C3 angle is 118.0° (Schmidbaur et al., 2004 ▸), very close to that observed in (II), which presents the same halogen substitution.

The 5-nitro substituent is almost conjugated with the benzene nucleus in (I): the dihedral angle between the NO₂ plane and the benzene ring is 6(2) and 1(2)° for each independent mol­ecule. For (II), twisting of the NO₂ groups is more significant, with dihedral angles of 10 (1) and 7(1)°. This near planar conformation is identical to that observed for 1,2,3-tri­chloro-5-nitro­benzene (Bhar et al., 1995 ▸), but contrasts with the twisted conformation observed in perhalogenated nitro­benzene derivatives: penta­chloro­nitro­benzene (twist angle of NO₂: 62°; Tanaka et al., 1974 ▸) and 1-bromo-2,3,5,6-tetra­fluoro-4-nitro­benzene (twist angle of NO₂: 41.7 (3)°; Stein et al., 2011 ▸). It thus seems clear that twisting of the nitro group with respect to the benzene ring in nitro­benzene derivatives is a direct consequence of intra­molecular crowding with ortho substituents. For 1,2,3-halogenated-5-nitro­benzenes such as (I) and (II), a planar conformation should be expected as a rule.

Supra­molecular features  

The crystal structures are directed by inter­molecular weak halogen bonds, also known as type-II inter­actions in the Desiraju classification scheme (Reddy et al., 2006 ▸). Such a bond is present in the asymmetric unit of (I), between Br2 and Br11 (Fig. 3 ▸). The type-II arrangement is characterized by angles θ ₁ = C2—Br2⋯Br11 and θ ₂ = C11—Br11⋯Br2, which should be close to 180 and 90°, respectively. For (I), observed angles are θ ₁ = 165.2 (5)° and θ ₂ = 82.3 (5)°. The crystal packing thus polarizes the involved halogen atoms, forming the halogen bond Br2^δ+⋯Br11^δ-. This dimolecular polar unit is connected via inversion centers to neighboring units in the cell, forming C—H⋯Br hydrogen bonds, and O⋯Br contacts. This packing motif induces secondary halogen⋯halogen contacts, which are clearly unpolarized. These type-I inter­actions are characterized by angles θ ₁ ≃ θ ₂ (Table 1 ▸, entries 2 and 3) and display larger Br⋯Br separations compared to the polarized halogen bond (entry 1), in which electrostatic forces bring the atoms into close contact.

Figure 3.

Part of the crystal structure of (I), emphasizing the halogen bonds (dashed lines). The green mol­ecules correspond to the asymmetric unit.

Table 1. Halogen-bond geometry (Å, °) for (I).

X 1⋯X 2	d	θ1	θ2	bond type
Br2⋯Br11	3.642 (3)	165.2 (5)	82.3 (5)	II-polarized
Br1⋯Br1i	3.731 (4)	133.3 (4)	133.3 (4)	I-unpolarized
Br2⋯Br13ii	3.781 (3)	126.8 (4)	129.6 (4)	I-unpolarized

Notes: d = separation X ₁⋯X ₂; θ₁ = angle C—X ₁⋯X ₂; θ₂ = angle X ₁⋯X ₂—C. For halogen bond types, see: Reddy et al. (2006 ▸). Symmetry codes: (i) −x, 1 − y, −z; (ii) −x, −y, 1 − z.

The substitution of one Br atom by I, to form crystal (II), changes dramatically the packing structure, affording a more complex network of halogen contacts (Fig. 4 ▸ and Table 2 ▸). Within the asymmetric unit, the type-II polarized contact is Br1⋯I12 (Table 2 ▸, entry 1). However, θ angles for this bond deviate from ideal values, and, surprisingly, the bond is polarized in the wrong way, Br^δ+⋯I^δ-. The opposite polarization was expected for this bond, due to the lower electronegativity and higher polarizability of iodine compared to bromine. The other significant contact observed in the asymmetric unit is a Br⋯Br unpolarized contact. The network of halogen bonds is expanded in the [100] direction by Br11, which gives a bifurcated contact with I2 and Br3 (Table 2 ▸, entries 2 and 4). One contact is polarized, with the polarization, once again, oriented in the unexpected way, I2^δ-⋯Br11^δ+. These anomalous halogen bonds are not present in other mixed halogen derivatives. Indeed, in 1,3-di­bromo-2-iodo­benzene (Schmidbaur et al., 2004 ▸), the iodine atom is not engaged in halogen bonding.

Figure 4.

Part of the crystal structure of (II), emphasizing the halogen bonds (dashed lines). The green mol­ecules correspond to the asymmetric unit.

Table 2. Halogen-bond geometry (Å, °) for (II).

X 1⋯X 2	d	θ1	θ2	bond type
Br1⋯I12	3.813 (2)	161.2 (4)	117.2 (4)	II-polarized
I2⋯Br11i	3.893 (2)	116.6 (4)	161.8 (4)	II-polarized
Br1⋯Br13	3.787 (2)	142.8 (4)	122.9 (4)	I-unpolarized
Br11⋯Br3ii	3.858 (2)	143.9 (4)	124.4 (4)	I-unpolarized

Notes: d = separation X ₁⋯X ₂; θ₁ = angle C—X ₁⋯X ₂; θ₂ = angle X ₁⋯X ₂—C. For halogen bond types, see: Reddy et al. (2006 ▸). Symmetry codes: (i) 1 + x, y, z; (ii) −1 + x, y, z.

Database survey  

The current release of the CSD (Version 5.36 with all updates; Groom & Allen, 2014 ▸), contains many structures of halogen-substituted nitro­benzene, with Cl (e.g. Bhar et al., 1995 ▸; Tanaka et al., 1974 ▸), Br (e.g. Olaru et al., 2014 ▸), and I (Thalladi et al., 1996 ▸). This series is completed with nitro­phenol deriv­atives, for example 2,3-di­fluoro-4-iodo-6-nitro­phenol (Francke et al., 2010 ▸). Structures of penta­chloro­phenol (Brezgunova et al., 2012 ▸) and penta­bromo­phenol (Betz et al., 2008 ▸; Brezgunova et al., 2012 ▸) are also available.

Regarding poly- and per-halogenated benzene structures, an impressive series of 23 compounds has been described, including Cl, Br, I and Me as substituents, generating a variety of mol­ecular symmetries (Reddy et al., 2006 ▸). The structure of D _6h-perhalogenated benzene has been reported with F (Shorafa et al., 2009 ▸), Cl (Brown & Strydom, 1974 ▸; Reddy et al., 2006 ▸), Br (Baharie & Pawley, 1979 ▸; Reddy et al., 2006 ▸; Brezgunova et al., 2012 ▸) and I (Ghosh et al., 2007 ▸). The former is a Z′ = 2 crystal, while others are Z′=1 crystals.

Synthesis and crystallization  

Compounds (I) and (II) were synthesized from 2,6-di­bromo-4-nitro­aniline (Bryant et al., 1998 ▸), as depicted in Fig. 5 ▸.

Figure 5.

Synthetic scheme for (I) and (II).

Synthesis of (I). A solution of 2,6-di­bromo-4-nitro­aniline (1.0 g, 3.38 mmol) in acetic acid (3 ml) was cooled to 278 K, and concentrated H₂SO₄ (7 ml) was carefully added under stirring. While ensuring that the temperature was still below 278 K, NaNO₂ (0.708 g, 10.26 mmol) was added in one batch. The reaction was stirred at this temperature for 2 h to afford the diazo­nium salt. An aqueous solution (17.67 ml) of CuBr (4.95 g, 34.54 mmol) and 47% HBr (17.67 ml) was warmed to 343 K, and the diazo­tization solution previously prepared was added in one batch with stirring. The mixture was kept at 343 K for 1 h, and then left to cool overnight. The reaction was neutralized with NaOH and extracted with CH₂Cl₂ (3 × 30 ml). The resulting solution was concentrated under vacuum and the crude material was purified by flash chromatography (petroleum ether/CH₂Cl₂ 8/2, R _f = 0.49) to give (I). Crystals were obtained by slow evaporation of a methanol/ethyl ether solution (yield: 0.952 g, 2.65 mmol, 78%). m.p. 380–382 K. IR (KBr, cm⁻¹): 3090 (Ar—H); 1583 (C=C); 1526, 1342 (N=O); 738 (C—Br). ¹H-NMR (600 MHz, CDCl₃): δ 8.43 (s, H-4, H-6). ¹³C-NMR (150 MHz, CDCl₃): δ 146.8, 135.7, 127.0, 126.9, 126.8. EIMS m/z: [M ⁺] 357 (34), [M ⁺+2] 359 (7), [M ⁺+4] 361 (100), [M ⁺+6] 363 (36) [M ⁺-NO₂] 311 (12).

Synthesis of (II). A solution of 2,6-di­bromo-4-nitro­aniline (1.0 g, 3.38 mmol) in acetic acid (3 ml) was cooled to 278 K in an ice-salt bath, and concentrated H₂SO₄ (3 ml) was carefully added under stirring. While ensuring that the temperature was still below 278 K, NaNO₂ (0.242 g, 3.516 mmol) was added in one batch. The reaction was stirred at this temperature for 30 min to afford the diazo­nium salt. An aqueous solution (10 ml) of KI (5.635 g, 33.95 mmol) was prepared, and the diazo­tization solution previously prepared was added in one batch. The mixture was then further stirred for 1 h. The reaction was neutralized with NaOH, extracted with CH₂Cl₂ (3 × 30 ml), and concentrated under vacuum. The crude material was purified by flash chromatography (petroleum ether/CH₂Cl₂ 4/1, R _f = 0.31) to give (II). Crystals were obtained by slow evaporation of an acetone/methanol/CH₂Cl₂ solution (yield: 1.21 g, 2.98 mmol, 88%). m.p. 415–417 K. IR (KBr, cm⁻¹): 3010 (Ar—H); 1620, 1516 (C=C); 1336 (N=O). ¹H-NMR (600 MHz, CDCl₃): δ 8.38 (s, H-4, H-6). ¹³C-NMR (150 MHz, CDCl₃): δ 146.1, 142.4, 127.4, 124.1. EIMS m/z: [M ⁺] 405 (42), [M ⁺+2] 407 (100), [M ⁺+4] 409 (48).

Refinement  

Crystal data, data collection and structure refinement details for (I) and (II) are summarized in Table 3 ▸. The absorption correction for (I) was challenging, and eventually carried out by applying DIFABS on the complete isotropic model (Walker & Stuart, 1983 ▸). In the case of (II), measured ψ-scans were used. H atoms were refined as riding to their carrier C atoms, with C—H bond lengths fixed at 0.93 Å and with U _iso(H) = 1.2U _eq(carrier atom).

Table 3. Experimental details.

	(I)	(II)
Crystal data
Chemical formula	C6H2Br3NO2	C6H2Br2INO2
M r	359.82	406.81
Crystal system, space group	Triclinic, P	Monoclinic, P21/c
Temperature (K)	298	298
a, b, c (Å)	7.641 (5), 8.040 (5), 14.917 (6)	13.548 (3), 20.037 (3), 9.123 (2)
α, β, γ (°)	83.91 (3), 79.86 (4), 81.49 (4)	90, 130.37 (2), 90
V (Å3)	889.2 (8)	1886.8 (8)
Z	4	8
Radiation type	Mo Kα	Mo Kα
μ (mm−1)	13.57	11.82
Crystal size (mm)	0.42 × 0.40 × 0.30	0.50 × 0.22 × 0.12
Data collection
Diffractometer	Bruker P4	Bruker P4
Absorption correction	Part of the refinement model (ΔF) (Walker & Stuart, 1983 ▸)	ψ scan (XSCANS; Bruker, 1997 ▸)
T min, T max	0.0002, 0.001	0.429, 0.988
No. of measured, independent and observed [I > 2σ(I)] reflections	6070, 3141, 1503	5716, 5407, 1968
R int	0.120	0.058
(sin θ/λ)max (Å−1)	0.596	0.703
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.066, 0.196, 1.47	0.061, 0.153, 0.95
No. of reflections	3141	5407
No. of parameters	218	218
H-atom treatment	H-atom parameters constrained	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.79, −1.00	0.84, −0.84

Computer programs: XSCANS (Bruker, 1997 ▸), SHELXS2014 (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸) and Mercury (Macrae et al., 2008 ▸).

Supplementary Material

CCDC references: 1412444, 1412445

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

(I) 1,2,3-Tribromo-5-nitrobenzene. Crystal data

C6H2Br3NO2	F(000) = 664
Mr = 359.82	Dx = 2.688 Mg m−3
Triclinic, P1	Melting point: 380 K
a = 7.641 (5) Å	Mo Kα radiation, λ = 0.71073 Å
b = 8.040 (5) Å	Cell parameters from 48 reflections
c = 14.917 (6) Å	θ = 4.8–12.4°
α = 83.91 (3)°	µ = 13.57 mm−1
β = 79.86 (4)°	T = 298 K
γ = 81.49 (4)°	Irregular, colourless
V = 889.2 (8) Å3	0.42 × 0.40 × 0.30 mm
Z = 4

(I) 1,2,3-Tribromo-5-nitrobenzene. Data collection

Bruker P4 diffractometer	1503 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.120
Graphite monochromator	θmax = 25.1°, θmin = 2.6°
ω scans	h = −8→9
Absorption correction: part of the refinement model (ΔF) (Walker & Stuart, 1983)	k = −9→9
Tmin = 0.0002, Tmax = 0.001	l = 0→17
6070 measured reflections	3 standard reflections every 97 reflections
3141 independent reflections	intensity decay: 1%

(I) 1,2,3-Tribromo-5-nitrobenzene. Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.066	H-atom parameters constrained
wR(F2) = 0.196	w = 1/[σ2(Fo2) + (0.050P)2] where P = (Fo2 + 2Fc2)/3
S = 1.47	(Δ/σ)max < 0.001
3141 reflections	Δρmax = 0.79 e Å−3
218 parameters	Δρmin = −1.00 e Å−3
0 restraints	Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 constraints	Extinction coefficient: 0.0063 (12)
Primary atom site location: structure-invariant direct methods

(I) 1,2,3-Tribromo-5-nitrobenzene. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.1438 (2)	0.3194 (2)	0.05082 (13)	0.0863 (6)
Br2	0.2958 (2)	0.0254 (2)	0.20089 (11)	0.0855 (6)
Br3	0.4312 (2)	−0.3604 (2)	0.13778 (10)	0.0791 (5)
C1	0.2177 (18)	0.1018 (19)	0.0215 (9)	0.070 (4)
C2	0.2831 (17)	−0.0235 (17)	0.0860 (9)	0.063 (3)
C3	0.3360 (14)	−0.1910 (16)	0.0555 (8)	0.056 (3)
C4	0.3227 (18)	−0.2259 (19)	−0.0296 (9)	0.069 (4)
H4	0.3573	−0.3355	−0.0465	0.083*
C5	0.2615 (17)	−0.1072 (16)	−0.0895 (10)	0.064 (3)
C6	0.2067 (16)	0.0562 (16)	−0.0661 (9)	0.059 (3)
H6	0.1619	0.1373	−0.1085	0.071*
N1	0.2502 (16)	−0.1453 (18)	−0.1809 (8)	0.075 (3)
O1	0.2967 (16)	−0.2925 (16)	−0.2012 (7)	0.094 (3)
O2	0.1923 (18)	−0.0342 (15)	−0.2318 (8)	0.105 (4)
Br11	0.3943 (2)	0.2012 (2)	0.39885 (13)	0.0891 (6)
Br12	0.1013 (2)	0.1170 (2)	0.58586 (10)	0.0795 (6)
Br13	−0.3231 (2)	0.2845 (2)	0.59130 (11)	0.0865 (6)
C11	0.151 (2)	0.2912 (18)	0.4092 (12)	0.077 (4)
C12	0.0303 (18)	0.2505 (18)	0.4860 (10)	0.064 (3)
C13	−0.150 (2)	0.323 (2)	0.4913 (9)	0.073 (4)
C14	−0.2002 (19)	0.4188 (19)	0.4208 (9)	0.070 (4)
H14	−0.3207	0.4619	0.4232	0.084*
C15	−0.079 (2)	0.4583 (18)	0.3427 (8)	0.068 (4)
C16	0.0943 (19)	0.3923 (18)	0.3375 (9)	0.068 (4)
H16	0.1756	0.4155	0.2850	0.082*
N11	−0.1327 (18)	0.5801 (16)	0.2644 (10)	0.076 (3)
O11	−0.2882 (14)	0.6432 (13)	0.2757 (7)	0.083 (3)
O12	−0.0224 (17)	0.5952 (18)	0.1956 (8)	0.110 (4)

(I) 1,2,3-Tribromo-5-nitrobenzene. Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Br1	0.0776 (11)	0.0671 (10)	0.1094 (12)	−0.0047 (8)	−0.0022 (9)	−0.0140 (8)
Br2	0.0876 (11)	0.0974 (13)	0.0716 (9)	−0.0124 (9)	−0.0075 (8)	−0.0164 (8)
Br3	0.0765 (10)	0.0789 (11)	0.0793 (10)	−0.0043 (8)	−0.0186 (8)	0.0070 (8)
C1	0.062 (8)	0.078 (10)	0.072 (9)	−0.013 (7)	−0.022 (7)	0.001 (7)
C2	0.058 (8)	0.068 (9)	0.062 (8)	−0.006 (7)	0.004 (6)	−0.026 (7)
C3	0.034 (6)	0.064 (8)	0.060 (7)	−0.001 (6)	0.001 (6)	0.012 (6)
C4	0.063 (8)	0.072 (9)	0.071 (9)	0.022 (7)	−0.018 (7)	−0.030 (7)
C5	0.056 (8)	0.051 (8)	0.087 (10)	−0.015 (6)	−0.021 (7)	0.009 (7)
C6	0.062 (8)	0.052 (8)	0.073 (8)	−0.019 (6)	−0.033 (7)	0.003 (6)
N1	0.079 (8)	0.081 (9)	0.080 (8)	−0.016 (7)	−0.036 (7)	−0.026 (7)
O1	0.119 (9)	0.095 (9)	0.071 (6)	−0.005 (7)	−0.017 (6)	−0.032 (6)
O2	0.151 (11)	0.087 (9)	0.089 (7)	−0.010 (8)	−0.061 (8)	0.004 (6)
Br11	0.0644 (10)	0.0993 (13)	0.1026 (12)	0.0018 (9)	−0.0185 (9)	−0.0137 (10)
Br12	0.0955 (12)	0.0701 (10)	0.0769 (9)	−0.0090 (8)	−0.0294 (9)	−0.0017 (7)
Br13	0.0785 (11)	0.0945 (13)	0.0808 (10)	−0.0202 (9)	0.0012 (8)	0.0067 (9)
C11	0.084 (10)	0.050 (8)	0.102 (11)	−0.013 (7)	−0.021 (9)	−0.015 (8)
C12	0.060 (8)	0.062 (8)	0.073 (9)	−0.018 (7)	−0.012 (8)	−0.008 (7)
C13	0.081 (10)	0.082 (10)	0.060 (8)	−0.020 (8)	−0.024 (7)	0.009 (7)
C14	0.056 (8)	0.080 (10)	0.065 (8)	−0.010 (7)	0.011 (7)	−0.007 (7)
C15	0.088 (10)	0.077 (10)	0.040 (6)	0.019 (8)	−0.034 (7)	−0.004 (6)
C16	0.070 (9)	0.072 (9)	0.062 (8)	−0.028 (8)	0.006 (7)	−0.003 (7)
N11	0.067 (8)	0.065 (8)	0.093 (10)	−0.005 (6)	−0.017 (7)	0.011 (7)
O11	0.074 (7)	0.079 (7)	0.099 (7)	0.003 (6)	−0.032 (6)	−0.014 (6)
O12	0.097 (8)	0.144 (12)	0.077 (7)	−0.012 (8)	−0.011 (7)	0.028 (7)

(I) 1,2,3-Tribromo-5-nitrobenzene. Geometric parameters (Å, º)

Br1—C1	1.831 (15)	Br11—C11	1.877 (15)
Br2—C2	1.821 (12)	Br12—C12	1.854 (14)
Br3—C3	1.886 (11)	Br13—C13	1.842 (15)
C1—C6	1.415 (18)	C11—C16	1.368 (19)
C1—C2	1.416 (18)	C11—C12	1.38 (2)
C2—C3	1.445 (18)	C12—C13	1.410 (19)
C3—C4	1.353 (17)	C13—C14	1.313 (18)
C4—C5	1.328 (17)	C14—C15	1.39 (2)
C4—H4	0.9300	C14—H14	0.9300
C5—C6	1.381 (19)	C15—C16	1.347 (19)
C5—N1	1.448 (18)	C15—N11	1.515 (16)
C6—H6	0.9300	C16—H16	0.9300
N1—O2	1.194 (15)	N11—O11	1.211 (15)
N1—O1	1.238 (16)	N11—O12	1.216 (16)
C6—C1—C2	119.0 (13)	C16—C11—C12	120.4 (14)
C6—C1—Br1	119.9 (9)	C16—C11—Br11	118.6 (13)
C2—C1—Br1	121.0 (10)	C12—C11—Br11	120.9 (11)
C1—C2—C3	116.2 (11)	C11—C12—C13	118.8 (13)
C1—C2—Br2	121.3 (10)	C11—C12—Br12	122.1 (10)
C3—C2—Br2	122.5 (9)	C13—C12—Br12	118.9 (10)
C4—C3—C2	121.8 (11)	C14—C13—C12	118.8 (14)
C4—C3—Br3	120.6 (10)	C14—C13—Br13	118.0 (11)
C2—C3—Br3	117.6 (9)	C12—C13—Br13	123.1 (10)
C5—C4—C3	121.5 (13)	C13—C14—C15	122.5 (13)
C5—C4—H4	119.3	C13—C14—H14	118.8
C3—C4—H4	119.3	C15—C14—H14	118.8
C4—C5—C6	120.7 (13)	C16—C15—C14	119.2 (11)
C4—C5—N1	121.1 (13)	C16—C15—N11	117.9 (13)
C6—C5—N1	118.2 (11)	C14—C15—N11	122.8 (12)
C5—C6—C1	120.8 (11)	C15—C16—C11	120.0 (14)
C5—C6—H6	119.6	C15—C16—H16	120.0
C1—C6—H6	119.6	C11—C16—H16	120.0
O2—N1—O1	123.6 (12)	O11—N11—O12	127.0 (13)
O2—N1—C5	118.3 (13)	O11—N11—C15	114.7 (13)
O1—N1—C5	118.1 (12)	O12—N11—C15	118.1 (12)
C6—C1—C2—C3	0.6 (19)	C16—C11—C12—C13	−4 (2)
Br1—C1—C2—C3	179.5 (9)	Br11—C11—C12—C13	179.1 (11)
C6—C1—C2—Br2	−178.5 (10)	C16—C11—C12—Br12	−178.9 (11)
Br1—C1—C2—Br2	0.3 (16)	Br11—C11—C12—Br12	4.0 (17)
C1—C2—C3—C4	−0.3 (19)	C11—C12—C13—C14	4 (2)
Br2—C2—C3—C4	178.8 (11)	Br12—C12—C13—C14	179.4 (12)
C1—C2—C3—Br3	178.0 (9)	C11—C12—C13—Br13	−178.0 (11)
Br2—C2—C3—Br3	−2.8 (14)	Br12—C12—C13—Br13	−2.7 (18)
C2—C3—C4—C5	1 (2)	C12—C13—C14—C15	−3 (2)
Br3—C3—C4—C5	−177.8 (11)	Br13—C13—C14—C15	178.7 (12)
C3—C4—C5—C6	−1 (2)	C13—C14—C15—C16	2 (2)
C3—C4—C5—N1	179.1 (13)	C13—C14—C15—N11	−174.8 (15)
C4—C5—C6—C1	1 (2)	C14—C15—C16—C11	−2 (2)
N1—C5—C6—C1	−178.8 (12)	N11—C15—C16—C11	175.4 (13)
C2—C1—C6—C5	−1 (2)	C12—C11—C16—C15	3 (2)
Br1—C1—C6—C5	−180.0 (10)	Br11—C11—C16—C15	179.8 (11)
C4—C5—N1—O2	179.2 (14)	C16—C15—N11—O11	−175.5 (13)
C6—C5—N1—O2	−1 (2)	C14—C15—N11—O11	1 (2)
C4—C5—N1—O1	1 (2)	C16—C15—N11—O12	10 (2)
C6—C5—N1—O1	−178.8 (13)	C14—C15—N11—O12	−173.5 (15)

(II) 1,3-Dibromo-2-iodo-5-nitrobenzene. Crystal data

C6H2Br2INO2	Dx = 2.864 Mg m−3
Mr = 406.81	Melting point: 415 K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 13.548 (3) Å	Cell parameters from 43 reflections
b = 20.037 (3) Å	θ = 5.7–12.5°
c = 9.123 (2) Å	µ = 11.82 mm−1
β = 130.37 (2)°	T = 298 K
V = 1886.8 (8) Å3	Prism, brown
Z = 8	0.50 × 0.22 × 0.12 mm
F(000) = 1472

(II) 1,3-Dibromo-2-iodo-5-nitrobenzene. Data collection

Bruker P4 diffractometer	1968 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.058
Graphite monochromator	θmax = 30.0°, θmin = 2.2°
2θ/ω scans	h = −14→19
Absorption correction: ψ scan (XSCANS; Bruker, 1997)	k = 0→28
Tmin = 0.429, Tmax = 0.988	l = −12→0
5716 measured reflections	3 standard reflections every 97 reflections
5407 independent reflections	intensity decay: 1%

(II) 1,3-Dibromo-2-iodo-5-nitrobenzene. Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.061	H-atom parameters constrained
wR(F2) = 0.153	w = 1/[σ2(Fo2) + (0.053P)2] where P = (Fo2 + 2Fc2)/3
S = 0.95	(Δ/σ)max < 0.001
5407 reflections	Δρmax = 0.84 e Å−3
218 parameters	Δρmin = −0.84 e Å−3
0 restraints	Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 constraints	Extinction coefficient: 0.00093 (11)
Primary atom site location: structure-invariant direct methods

(II) 1,3-Dibromo-2-iodo-5-nitrobenzene. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.30362 (13)	0.43988 (8)	0.2401 (2)	0.0615 (4)
I2	0.54556 (10)	0.36925 (4)	0.26460 (13)	0.0583 (3)
Br3	0.73278 (12)	0.49074 (7)	0.26614 (18)	0.0561 (4)
C1	0.4175 (11)	0.4967 (7)	0.2453 (16)	0.035 (3)
C2	0.5191 (11)	0.4723 (6)	0.2535 (13)	0.033 (3)
C3	0.5960 (11)	0.5182 (6)	0.2557 (17)	0.038 (3)
C4	0.5754 (12)	0.5862 (6)	0.2478 (17)	0.040 (3)
H4A	0.6264	0.6171	0.2474	0.048*
C5	0.4763 (13)	0.6050 (7)	0.2405 (15)	0.046 (4)
C6	0.3965 (12)	0.5642 (7)	0.2397 (18)	0.048 (4)
H6A	0.3307	0.5809	0.2355	0.057*
N1	0.4555 (13)	0.6807 (6)	0.2380 (17)	0.065 (3)
O1	0.5145 (11)	0.7161 (5)	0.2088 (17)	0.085 (4)
O2	0.3795 (15)	0.6989 (5)	0.2557 (18)	0.105 (4)
Br11	−0.18918 (13)	0.30721 (8)	0.2488 (2)	0.0620 (4)
I12	0.04866 (10)	0.37922 (4)	0.26639 (13)	0.0593 (3)
Br13	0.24427 (12)	0.25893 (8)	0.2825 (2)	0.0588 (4)
C11	−0.0736 (11)	0.2509 (7)	0.2562 (17)	0.039 (3)
C12	0.0237 (12)	0.2769 (7)	0.2619 (14)	0.035 (3)
C13	0.1046 (11)	0.2312 (6)	0.2672 (18)	0.039 (3)
C14	0.0869 (13)	0.1639 (6)	0.2665 (18)	0.045 (4)
H14A	0.1429	0.1344	0.2736	0.054*
C15	−0.0137 (13)	0.1391 (8)	0.2553 (16)	0.045 (4)
C16	−0.0922 (13)	0.1829 (6)	0.2507 (18)	0.043 (4)
H16A	−0.1596	0.1668	0.2437	0.052*
N11	−0.0302 (15)	0.0681 (6)	0.2483 (17)	0.066 (4)
O11	0.0350 (12)	0.0323 (6)	0.2418 (18)	0.099 (4)
O12	−0.1106 (14)	0.0493 (6)	0.2609 (17)	0.099 (4)

(II) 1,3-Dibromo-2-iodo-5-nitrobenzene. Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Br1	0.0558 (8)	0.0680 (9)	0.0684 (9)	−0.0167 (7)	0.0437 (7)	−0.0035 (7)
I2	0.0737 (6)	0.0268 (4)	0.0723 (7)	0.0048 (5)	0.0464 (5)	0.0017 (4)
Br3	0.0484 (7)	0.0636 (9)	0.0654 (9)	0.0047 (7)	0.0409 (7)	0.0002 (7)
C1	0.041 (7)	0.035 (7)	0.033 (6)	−0.012 (6)	0.027 (5)	−0.007 (5)
C2	0.043 (7)	0.017 (6)	0.035 (8)	0.002 (5)	0.024 (6)	0.000 (4)
C3	0.042 (6)	0.033 (7)	0.041 (7)	0.003 (5)	0.028 (6)	−0.004 (5)
C4	0.037 (7)	0.036 (8)	0.048 (8)	−0.005 (6)	0.027 (6)	−0.003 (6)
C5	0.046 (7)	0.023 (7)	0.040 (8)	0.005 (6)	0.015 (6)	−0.002 (5)
C6	0.036 (7)	0.064 (10)	0.045 (8)	−0.003 (7)	0.027 (6)	−0.016 (7)
N1	0.066 (8)	0.031 (7)	0.075 (9)	0.010 (7)	0.036 (7)	−0.001 (6)
O1	0.091 (8)	0.030 (6)	0.108 (9)	−0.003 (6)	0.053 (7)	0.003 (6)
O2	0.163 (12)	0.050 (7)	0.137 (11)	0.050 (8)	0.112 (10)	0.016 (6)
Br11	0.0522 (8)	0.0681 (9)	0.0685 (9)	0.0108 (7)	0.0404 (7)	−0.0033 (7)
I12	0.0755 (6)	0.0283 (4)	0.0735 (7)	−0.0069 (5)	0.0479 (5)	−0.0038 (4)
Br13	0.0488 (7)	0.0631 (9)	0.0703 (9)	−0.0088 (7)	0.0412 (7)	−0.0014 (7)
C11	0.043 (7)	0.035 (7)	0.041 (7)	−0.002 (6)	0.028 (6)	0.002 (6)
C12	0.041 (7)	0.033 (8)	0.039 (8)	0.007 (6)	0.030 (6)	0.004 (4)
C13	0.033 (6)	0.037 (8)	0.042 (7)	−0.005 (5)	0.022 (6)	−0.005 (6)
C14	0.051 (8)	0.029 (7)	0.044 (8)	0.008 (6)	0.025 (6)	0.000 (6)
C15	0.063 (9)	0.028 (7)	0.056 (9)	−0.015 (6)	0.045 (8)	−0.006 (5)
C16	0.046 (7)	0.031 (7)	0.042 (7)	−0.021 (6)	0.024 (6)	−0.015 (5)
N11	0.096 (10)	0.034 (7)	0.073 (9)	−0.018 (7)	0.057 (8)	−0.006 (6)
O11	0.101 (9)	0.029 (6)	0.147 (11)	−0.010 (6)	0.072 (8)	−0.005 (7)
O12	0.144 (11)	0.061 (7)	0.130 (10)	−0.042 (8)	0.106 (9)	−0.012 (6)

(II) 1,3-Dibromo-2-iodo-5-nitrobenzene. Geometric parameters (Å, º)

Br1—C1	1.894 (12)	Br11—C11	1.895 (14)
I2—C2	2.088 (12)	I12—C12	2.074 (14)
Br3—C3	1.875 (13)	Br13—C13	1.888 (13)
C1—C6	1.375 (18)	C11—C12	1.387 (17)
C1—C2	1.416 (17)	C11—C16	1.381 (18)
C2—C3	1.380 (17)	C12—C13	1.405 (17)
C3—C4	1.384 (16)	C13—C14	1.370 (16)
C4—C5	1.353 (18)	C14—C15	1.390 (19)
C4—H4A	0.9300	C14—H14A	0.9300
C5—C6	1.35 (2)	C15—C16	1.359 (19)
C5—N1	1.539 (18)	C15—N11	1.435 (19)
C6—H6A	0.9300	C16—H16A	0.9300
N1—O2	1.199 (17)	N11—O11	1.168 (19)
N1—O1	1.221 (19)	N11—O12	1.226 (18)
C6—C1—C2	120.8 (13)	C12—C11—C16	121.2 (14)
C6—C1—Br1	116.4 (11)	C12—C11—Br11	121.4 (11)
C2—C1—Br1	122.8 (10)	C16—C11—Br11	117.3 (11)
C3—C2—C1	118.1 (12)	C11—C12—C13	117.3 (13)
C3—C2—I2	123.6 (10)	C11—C12—I12	120.7 (11)
C1—C2—I2	118.4 (10)	C13—C12—I12	122.0 (10)
C2—C3—C4	122.0 (13)	C14—C13—C12	120.8 (13)
C2—C3—Br3	121.2 (10)	C14—C13—Br13	117.0 (11)
C4—C3—Br3	116.8 (11)	C12—C13—Br13	122.2 (10)
C5—C4—C3	115.9 (13)	C13—C14—C15	120.8 (14)
C5—C4—H4A	122.0	C13—C14—H14A	119.6
C3—C4—H4A	122.0	C15—C14—H14A	119.6
C4—C5—C6	126.6 (14)	C16—C15—C14	118.8 (14)
C4—C5—N1	116.2 (15)	C16—C15—N11	122.8 (14)
C6—C5—N1	117.2 (15)	C14—C15—N11	118.3 (15)
C5—C6—C1	116.7 (13)	C15—C16—C11	121.0 (14)
C5—C6—H6A	121.7	C15—C16—H16A	119.5
C1—C6—H6A	121.7	C11—C16—H16A	119.5
O2—N1—O1	126.4 (14)	O11—N11—O12	124.2 (16)
O2—N1—C5	117.6 (14)	O11—N11—C15	120.6 (18)
O1—N1—C5	115.9 (17)	O12—N11—C15	115.0 (15)
C6—C1—C2—C3	0.0 (16)	C16—C11—C12—C13	−1.7 (16)
Br1—C1—C2—C3	179.7 (9)	Br11—C11—C12—C13	180.0 (9)
C6—C1—C2—I2	179.4 (9)	C16—C11—C12—I12	179.2 (9)
Br1—C1—C2—I2	−1.0 (12)	Br11—C11—C12—I12	0.8 (13)
C1—C2—C3—C4	−0.8 (17)	C11—C12—C13—C14	0.1 (17)
I2—C2—C3—C4	179.9 (9)	I12—C12—C13—C14	179.2 (9)
C1—C2—C3—Br3	−179.9 (9)	C11—C12—C13—Br13	−178.2 (9)
I2—C2—C3—Br3	0.7 (14)	I12—C12—C13—Br13	0.9 (14)
C2—C3—C4—C5	0.9 (18)	C12—C13—C14—C15	1.7 (19)
Br3—C3—C4—C5	−179.9 (9)	Br13—C13—C14—C15	−179.9 (10)
C3—C4—C5—C6	−0.2 (18)	C13—C14—C15—C16	−1.9 (18)
C3—C4—C5—N1	178.2 (11)	C13—C14—C15—N11	177.8 (12)
C4—C5—C6—C1	−0.5 (19)	C14—C15—C16—C11	0.3 (18)
N1—C5—C6—C1	−178.9 (10)	N11—C15—C16—C11	−179.5 (12)
C2—C1—C6—C5	0.6 (17)	C12—C11—C16—C15	1.6 (19)
Br1—C1—C6—C5	−179.1 (9)	Br11—C11—C16—C15	180.0 (10)
C4—C5—N1—O2	−171.0 (13)	C16—C15—N11—O11	175.7 (14)
C6—C5—N1—O2	7.6 (18)	C14—C15—N11—O11	−4 (2)
C4—C5—N1—O1	12.4 (17)	C16—C15—N11—O12	−8.3 (19)
C6—C5—N1—O1	−169.1 (12)	C14—C15—N11—O12	171.9 (13)