Halogen bonding in 1,2-dibromo-4,5-dimethoxy­benzene and 1,2-diiodo-4,5-dimethoxy­benzene

An interesting case of `halogen-bonding-promoted' crystal structure architecture is presented. The two title compounds, C₈H₈Br₂O₂ and C₈H₈I₂O₂, have almost indistinguishable mol­ecular structures but very different spatial organization, and this is mainly due to differences in the halogen-bonding inter­actions in which the different species present, i.e. Br and I, take part. The dibromo structure exhibits a [pi]-bonded columnar array involving all four independent mol­ecules in the asymmetric unit, with inter­columnar inter­actions governed by C-Br...Br-C links and with no C-Br...O/N inter­actions present. In the diiodo structure, instead, the C-I...O synthon prevails, defining linear chains, in turn inter­linked by C-I...I-C inter­actions.

S1. Comment

For many years, interest in the study of noncovalent interactions has been monopolized almost entirely by hydrogen bonding and, more recently, π–π and C—H···π interactions. The driving force for this interest was (and still is) the fundamental role these interactions play in molecular recognition, a chemical process basic to life itself but nowadays also closely related to many frontier technology enterprises. In the past few years, however, a different (though closely related) type of noncovalent interactions has begun to attract the scientist's attention, the so called `halogen bond', where the main actor is a highly polarized halogen species. Under this wide umbrella, however, shelter a large variety of interactions of different aspects and behaviours; since only some of these will be used in the present work we will briefly introduce them here, directing the interested reader to more specific and qualified literature (e.g. Metrangolo et al., 2007).

In particular, we shall deal with interactions of the C—X···O/N and C—X···X—C type (where X is a halogen). The main aspects of the former type are quite in tune with the conventional hydrogen bond, and accordingly its most conspicuous geometrical characteristics are (a) a rather large C—X···O/N angle (> 150°) and (b) an X···O distance shorter than the sum of the van der Waals radii. The second type is rather more complex from a descriptive point of view, but the main aspects could be summarized as follows: If we denote the larger of the two C—X···X angles as θ₁, and the smaller as θ₂, then two types of C—X···X—C interactions can be envisaged (Desiraju & Parthasarathy, 1989): the (so-called) I1 interactions, which have θ₁ = θ₂, and the I2 interactions, which have θ₁ ≈ 180 ° and θ₂ ≈ 90 °. In both cases, the X···X distance is shorter than the sum of the van der Waals radii.

The structures reported herein correspond to some of the simplest systems where this type of interaction can take place: a couple of dihalogenated aryl derivatives, namely 1,2-dibromo-4,5-dimethoxybenzene, C₈H₈Br₂O₂, (I) (or dibromo veratrole), and 1,2-diiodo-4,5-dimethoxybenzene, C₈H₈I₂O₂, (II) (or diiodo veratrole). Diiodo veratrole is a versatile starting point in many chemical reactions, including the synthesis of electron-rich phtalocyanines, conductive polymers (Bhongale et al., 2006) and cathecol-based ligands (Kinder & Youngs, 1996). It belongs to the same family of diiodobenzene, but the methoxy substituents makes this compound more electron-rich, thus rendering it more reactive towards electrophiles. The crystal structures of these closely related compounds are governed by a variety of nonbonding interactions, but the leading organizing forces are the above-mentioned `halogen bonds', which differences we will discuss in detail.

The asymmetric unit of (I) is composed of four identical, though non-equivalent, C₈H₈Br₂O₂ molecules (A–D, Fig. 1), disposed one on top of the other in an almost perfect 4₁ arrangement, with a relative rotation of ~π/2 and a graphitic translation shift (range \sim 3.64–3.80 Å; Table 1) when going from one to the next. This almost perfect columnar disposition is maintained by the fact that the array is continued via two inversion operations with their centres in the column axis, at (0, 1, 1/2) and (1/2, 0, 0) (marked as x and y in Fig. 2).

This preserves the alignment along the [121] columnar direction of the π-bonded chain, while disrupting the pseudo 4₁ piling sequence, turning it into a ···ABCD–DCBA–ABCD··· array (Fig. 2) with D–D and A–A related by inversion operations, and at a slightly longer than typical center-to-center distance [4.061 (1) and 4.227 (1) Å, respectively; Table 1]. The columnar alignment seems to be the consequence of both π–π and dipolar C—O—C interactions: the dipole of the C3/O1/C7 ether group is almost aligned with that of the C4/O2/C8 group of the adjacent molecule, but with opposite sense (see Fig. 1).

Besides these π–π interactions connecting aromatic rings in a columnar-like array, the structure presents some other nonbonding interactions at nearly right angles to the column direction, of which the most important are the C—Br···Br—C (type I2) halogen-bond contacts linking molecules with their nearest neighbours. The most relevant of these contacts (d < 3.9 Å) are shown in Fig. 1 and Table 2, all of them fulfilling the above-mentioned conditions for an I2 interaction (first four entries) and for an I1 interaction (last two entries). There are in addition a couple of nonconventional C—H···O bonds, presented in Table 3. All these interactions link neighbouring chains together into a densely connected three-dimensional structure (Fig. 3).

At a molecular level, (II) (Fig. 4) is almost identical to its Br analogue (I).

The main interactions in the structure are mediated by the halogen atoms, and in this respect the situation is highly asymmetric, atom I2 being much more active than I1. The strongest interaction is the head-to-tail link in which I2 makes a bifurcated contact with atoms O1 and O2 in a neighbouring molecule (Table 4 and Fig. 4), thus defining a wavy chain running along the b-axis direction. These chains, in turn, are linked by a halogen–halogen contact (Table 5), into an, also wavy, two-dimensional structure parallel to (100). Both interactions are illustrated as broken lines in Fig. 4, where the two-dimensional array is shown; Fig. 5, in turn, exemplifies though a side view of the latter the wavy nature of the chain juxtaposition. Piling of these two-dimensional elements promotes a couple of π interactions of different type, viz. a π–π contact (Table 6) and a C—H···π hydrogen bond (Table 7), which link the two-dimensional structures into a three-dimensional one.

Thus, we have described two compounds that present almost indistinguishable molecular structures but which, in spite of the molecular similarities, give rise to absolutely different packing arrangements, and this seems to be a result of the different strengths of the C—X···O and C—X···X—C interactions as a result of the change in the corresponding halogen species involved. In this respect, the C—Br···Br—C interaction appears to be much more feasible than C—Br···O [not a single example of the latter interaction is present in (I)]; conversely, the main synthon in (II), which leads to the formation of the chains, is constructed out of the C—I···O link, the C—I···I—C interaction appearing as second order and serving as an interchain linkage.

It is to be expected that these types of interactions will become more fully recognized and their incidence in crystal architectures will be analyzed in more detail, so that better and more efficient ab initio molecular designs can be achieved through their statistical rationalization.

Related literature

For related literature, see: Bhongale et al. (2006); Desiraju & Parthasarathy (1989); Kinder & Youngs (1996); Metrangolo et al. (2007).

S2. Experimental

Both compounds were prepared by direct halogenation of dimethoxybenzene, using Br₂ and ICl for the dibromo and diiodo compounds, respectively.

For the synthesis of (I), in a three-necked 250 ml flask equipped with a thermometer and a pressure-compensated addition funnel were placed veratrole (10.141 g) and dichloromethane (125 ml) with a magnetic stirring bar. The flask was placed in an ice-bath, and while the mixture cooled to 278 K, a hose with a funnel was attached to the remaining neck. The funnel was carefully placed facing down just over the surface of an Na₂CO₃ solution, in such a way that the acid vapours generated would be neutralized by the carbonate. A solution of Br₂ (8 ml) in CH₂Cl₂ (20 ml) was loaded on the addition funnel and added dropwise with continuous stirring for a period of 1 h. The ice-bath was removed and the solution was stirred overnight. The contents of the flask were carefully poured into a separation funnel containing a solution of sodium bisulphite. The organic phase was washed with water, Na₂CO₃ and water again, dried over MgSO₄, and evaporated. The crude product was recrystallized from ethanol until no traces of the monobrominated product were detected by thin-layer chromatography, yielding 20.96 g (96%) of white [colourless according to CIF] crystals (m.p. 362–364 K).

The diiodo compound was prepared in a similar fashion to the brominated analogue. Namely, veratrole (9.106 g), dichloromethane (125 ml) and a magnetic stirring bar were placed in a 250 ml three-necked flask. The mixture was cooled to 278 K using an ice-bath, and a pressure-compensated addition funnel and a system for the evacuation of the generated acidic vapours similar to that used in the synthesis of the dibromo compound were attached to the flask. A solution of ICl (22.5 g) in CH₂Cl₂ (20 ml) was loaded into the addition funnel and then added slowly dropwise (0.2 ml min^-1), with continuous stirring. The cold bath was removed, and after 1 h of stirring at room temperature, the solution was poured into a separation funnel containing sodium bisulphite. The organic phase was separated, washed with water, Na₂CO₃ and then water again, and dried over MgSO₄. The solvent was evaporated and the purple tar obtained was passed quickly through a fritted disc funnel filled with a short column of silica, eluting with a mixture of dichloromethane and cyclohexane. The almost colourless solution was evaporated and the white solid was recrystallized several times from ethanol, yielding 18.22 g (70.9%) of white needles [colourless blocks according to CIF] (m.p. 404–405 K).

Crystals of both compounds were obtained by slow evaporation of an ethanol solution of the corresponding dihalodimethoxybenzene. Depending on the speed of evaporation, crystals with dimensions ranging from less than a millimeter up to a centimeter were obtained. Both compounds showed ¹H NMR spectra consistent on two singlets, one corresponding to the aromatic H atoms (at 7.06 and 7.23 p.p.m. for the dibromo and diiodo compounds) and one corresponding to the methoxy H atoms at 3.83 p.p.m. Elemental analysis: expected (calculated) for C₈H₈O₂Br₂: C 32.6 (32.47), H 2.7 (2.72)%; for C₈H₈O₂I₂: C 24.8 (24.64), H 2.1 (2.07)%.

S3. Refinement

H atoms were placed at calculated positions [C—H = 0.93 Å (aromatic) and 0.96 Å (methyl)] and allowed to ride; methyl groups were allowed to rotate as well. U_iso(H) values were taken as xU_eq(host) [x = 1.2 (aromatic) and 1.5 (methyl)].

Computing details

Data collection: SMART (Bruker, 2001) for (I); MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988) for (II). Cell refinement: SAINT (Bruker, 2002) for (I); MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988) for (II). Data reduction: SAINT (Bruker, 2002) for (I); MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988) for (II). For both compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2003).

Figures

	Fig. 1. The asymmetric unit of (I), showing the four independent molecules (labelled A–D), with displacement ellipsoids drawn at the 40% probability level. Unlabelled atoms follow the same label sequence as molecule A. π–π bonds are represented by dashed lines connecting ring centres and Br···Br interactions by double-dashed lines. [Symmetry codes: (i) -x + 1, -y + 2, -z + 1; (ii) -x, -y +1, -z + 1; (iii) -x, -y, -z; (iv) -x + 1, -y + 1, -z; (v) -x + 1, -y + 1, -z + 1; (vi) -x, -y +1, -z.]
	Fig. 2. A view of the packing (I), showing the way in which a column is formed (see text).
	Fig. 3. A view of the packing (I), projected down [121], the column direction, and showing the way in which parallel chains interact to form a three-dimensional structure.
	Fig. 4. The two-dimensional structure in (II), parallel to (100), with displacement ellipsoids drawn at the 40% probability level. [Symmetry codes: (i) -x + 1/2, -y + 1, z + 1/2, (ii) -x + 1/2, y - 1/2, z.]
	Fig. 5. The same two-dimensional structure as in Fig. 4, viewed at right angles and revealing its `wavy' character.

(I) 1,2-Dibromo-4,5-dimethoxybenzene

Crystal data

C8H8Br2O2	Z = 8
Mr = 295.96	F(000) = 1136
Triclinic, P1	Dx = 2.020 Mg m^−3
Hall symbol: -P 1	Melting point: 363(1) K
a = 10.1172 (5) Å	Mo Kα radiation, λ = 0.71073 Å
b = 10.2052 (5) Å	Cell parameters from 6539 reflections
c = 20.2764 (10) Å	θ = 2.5–24.7°
α = 104.1710 (12)°	µ = 8.29 mm^−1
β = 98.9405 (10)°	T = 294 K
γ = 101.0630 (12)°	Blocks, colourless
V = 1946.46 (17) Å^3	0.16 × 0.14 × 0.14 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer	8656 independent reflections
Radiation source: fine-focus sealed tube	5046 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.033
phi and ω scans	θmax = 27.9°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Bruker, 2002)	h = −13→13
Tmin = 0.28, Tmax = 0.32	k = −13→13
30774 measured reflections	l = −26→26

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)] = 0.036	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.097	H-atom parameters constrained
S = 1.02	w = 1/[σ^2(Fo^2) + (0.038P)^2 + 0.6302P] where P = (Fo^2 + 2Fc^2)/3
8656 reflections	(Δ/σ)max = 0.001
441 parameters	Δρmax = 0.44 e Å^−3
0 restraints	Δρmin = −0.46 e Å^−3

Special details

Experimental. Characterization was performed by NMR (Bruker Avance300 using CDCl3 as solvent and its residual peak as internal reference at 7.26 p.p.m.) and elemental analysis (Carlo Erba CHNS-O EA1108 at the Servicio de Microanálisis of Inquimae).

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1A	0.18852 (5)	0.84633 (5)	0.56347 (2)	0.08861 (16)
Br2A	−0.11747 (5)	0.62952 (5)	0.47438 (2)	0.08819 (15)
O1A	0.1572 (3)	1.0684 (3)	0.35540 (14)	0.0836 (8)
O2A	−0.0780 (3)	0.9081 (3)	0.29058 (14)	0.0872 (9)
C1A	0.0987 (4)	0.8591 (4)	0.47729 (18)	0.0612 (9)
C2A	0.1624 (4)	0.9604 (4)	0.44997 (19)	0.0646 (10)
H2A	0.2471	1.0193	0.4743	0.077*
C3A	0.1027 (4)	0.9747 (4)	0.38795 (18)	0.0645 (10)
C4A	−0.0254 (4)	0.8857 (4)	0.35145 (18)	0.0657 (10)
C5A	−0.0879 (4)	0.7858 (4)	0.37868 (19)	0.0668 (10)
H5A	−0.1727	0.7269	0.3546	0.080*
C6A	−0.0262 (4)	0.7716 (4)	0.44160 (18)	0.0618 (9)
C7A	0.2883 (4)	1.1603 (5)	0.3899 (2)	0.0869 (13)
H7AA	0.3152	1.2215	0.3626	0.130*
H7AB	0.3556	1.1069	0.3954	0.130*
H7AC	0.2821	1.2141	0.4348	0.130*
C8A	−0.2073 (4)	0.8181 (6)	0.2512 (2)	0.1095 (18)
H8AA	−0.2320	0.8416	0.2086	0.164*
H8AB	−0.2770	0.8292	0.2779	0.164*
H8AC	−0.1997	0.7232	0.2407	0.164*
Br1B	0.51028 (5)	0.84947 (5)	0.39054 (2)	0.09023 (16)
Br2B	0.40577 (5)	0.60365 (5)	0.46979 (2)	0.08438 (15)
O1B	0.0405 (3)	0.6253 (3)	0.21122 (14)	0.0760 (8)
O2B	−0.0379 (3)	0.4381 (3)	0.27175 (14)	0.0773 (7)
C1B	0.3397 (4)	0.7172 (4)	0.35633 (19)	0.0602 (9)
C2B	0.2559 (4)	0.7211 (4)	0.29605 (19)	0.0640 (10)
H2B	0.2854	0.7874	0.2738	0.077*
C3B	0.1298 (4)	0.6281 (4)	0.26885 (18)	0.0587 (9)
C4B	0.0868 (4)	0.5265 (4)	0.30234 (19)	0.0594 (9)
C5B	0.1704 (4)	0.5233 (4)	0.36135 (18)	0.0604 (9)
H5B	0.1421	0.4564	0.3835	0.073*
C6B	0.2966 (4)	0.6177 (4)	0.38877 (18)	0.0599 (9)
C7B	0.0833 (5)	0.7271 (5)	0.1756 (2)	0.0865 (13)
H7BA	0.0120	0.7163	0.1361	0.130*
H7BB	0.1661	0.7138	0.1603	0.130*
H7BC	0.1003	0.8189	0.2068	0.130*
C8B	−0.0872 (4)	0.3350 (4)	0.3047 (2)	0.0772 (11)
H8BA	−0.1749	0.2779	0.2777	0.116*
H8BB	−0.0971	0.3800	0.3505	0.116*
H8BC	−0.0226	0.2780	0.3081	0.116*
Br1C	0.15911 (5)	0.45176 (5)	0.02682 (2)	0.09230 (17)
Br2C	0.47373 (5)	0.65530 (5)	0.11271 (2)	0.08761 (16)
O1C	0.1936 (3)	0.2113 (3)	0.22690 (13)	0.0698 (7)
O2C	0.4349 (3)	0.3628 (3)	0.29126 (13)	0.0693 (7)
C1C	0.2523 (4)	0.4309 (4)	0.11005 (18)	0.0610 (9)
C2C	0.1871 (4)	0.3281 (4)	0.13655 (19)	0.0619 (9)
H2C	0.1005	0.2725	0.1129	0.074*
C3C	0.2494 (4)	0.3082 (4)	0.19688 (18)	0.0572 (9)
C4C	0.3800 (4)	0.3909 (4)	0.23244 (17)	0.0559 (9)
C5C	0.4440 (4)	0.4937 (4)	0.20656 (18)	0.0585 (9)
H5C	0.5303	0.5502	0.2302	0.070*
C6C	0.3789 (4)	0.5125 (4)	0.14515 (19)	0.0595 (9)
C7C	0.0615 (4)	0.1217 (4)	0.1909 (2)	0.0764 (11)
H7CA	0.0294	0.0632	0.2185	0.115*
H7CB	0.0696	0.0648	0.1470	0.115*
H7CC	−0.0028	0.1771	0.1830	0.115*
C8C	0.5725 (4)	0.4376 (5)	0.3258 (2)	0.0782 (12)
H8CA	0.6008	0.4056	0.3652	0.117*
H8CB	0.5761	0.5352	0.3411	0.117*
H8CC	0.6331	0.4222	0.2941	0.117*
Br1D	0.13475 (5)	−0.12779 (5)	0.02042 (2)	0.08027 (14)
Br2D	0.26373 (5)	0.09162 (5)	−0.06800 (2)	0.08695 (15)
O1D	0.5780 (3)	0.1239 (3)	0.21456 (13)	0.0792 (8)
O2D	0.6751 (3)	0.2925 (3)	0.14934 (13)	0.0783 (8)
C1D	0.3045 (4)	0.0067 (4)	0.05654 (18)	0.0573 (9)
C2D	0.3764 (4)	0.0138 (4)	0.12185 (18)	0.0602 (9)
H2D	0.3411	−0.0468	0.1459	0.072*
C3D	0.4984 (4)	0.1094 (4)	0.15087 (18)	0.0608 (9)
C4D	0.5534 (4)	0.2009 (4)	0.11520 (18)	0.0618 (9)
C5D	0.4818 (4)	0.1936 (4)	0.05073 (18)	0.0620 (9)
H5D	0.5171	0.2538	0.0265	0.074*
C6D	0.3564 (4)	0.0962 (4)	0.02122 (18)	0.0596 (9)
C7D	0.5192 (5)	0.0460 (5)	0.2567 (2)	0.0939 (15)
H7DA	0.5817	0.0683	0.3008	0.141*
H7DB	0.5026	−0.0517	0.2338	0.141*
H7DC	0.4338	0.0688	0.2638	0.141*
C8D	0.7344 (4)	0.3886 (4)	0.1158 (2)	0.0839 (12)
H8DA	0.8199	0.4464	0.1450	0.126*
H8DB	0.6723	0.4457	0.1071	0.126*
H8DC	0.7512	0.3387	0.0724	0.126*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1A	0.0960 (3)	0.0955 (3)	0.0719 (3)	0.0127 (3)	−0.0071 (2)	0.0427 (2)
Br2A	0.1043 (4)	0.0785 (3)	0.0778 (3)	−0.0019 (3)	0.0137 (3)	0.0368 (2)
O1A	0.0754 (19)	0.102 (2)	0.0684 (17)	−0.0081 (16)	0.0056 (14)	0.0438 (16)
O2A	0.0713 (18)	0.124 (2)	0.0612 (16)	−0.0050 (17)	−0.0042 (14)	0.0500 (16)
C1A	0.070 (3)	0.070 (2)	0.0483 (19)	0.024 (2)	0.0111 (18)	0.0212 (18)
C2A	0.059 (2)	0.073 (3)	0.057 (2)	0.0090 (19)	0.0055 (18)	0.0204 (19)
C3A	0.065 (2)	0.075 (3)	0.053 (2)	0.006 (2)	0.0108 (18)	0.0265 (19)
C4A	0.064 (2)	0.084 (3)	0.050 (2)	0.009 (2)	0.0092 (18)	0.0277 (19)
C5A	0.060 (2)	0.078 (3)	0.057 (2)	0.005 (2)	0.0086 (18)	0.020 (2)
C6A	0.071 (3)	0.060 (2)	0.057 (2)	0.013 (2)	0.0166 (19)	0.0212 (18)
C7A	0.075 (3)	0.094 (3)	0.086 (3)	−0.004 (2)	0.011 (2)	0.039 (3)
C8A	0.072 (3)	0.169 (5)	0.075 (3)	−0.013 (3)	−0.009 (2)	0.058 (3)
Br1B	0.0765 (3)	0.0857 (3)	0.0943 (3)	−0.0094 (2)	−0.0129 (2)	0.0412 (3)
Br2B	0.0791 (3)	0.1052 (3)	0.0695 (3)	0.0147 (3)	−0.0057 (2)	0.0450 (2)
O1B	0.0723 (18)	0.0818 (18)	0.0744 (17)	0.0076 (14)	−0.0081 (14)	0.0466 (15)
O2B	0.0623 (17)	0.0847 (19)	0.0833 (18)	0.0007 (15)	−0.0009 (14)	0.0444 (15)
C1B	0.055 (2)	0.059 (2)	0.062 (2)	0.0094 (18)	0.0004 (17)	0.0202 (18)
C2B	0.070 (3)	0.063 (2)	0.064 (2)	0.015 (2)	0.0088 (19)	0.0334 (19)
C3B	0.058 (2)	0.064 (2)	0.059 (2)	0.0192 (19)	0.0036 (18)	0.0277 (18)
C4B	0.054 (2)	0.066 (2)	0.062 (2)	0.0144 (19)	0.0083 (18)	0.0278 (19)
C5B	0.057 (2)	0.069 (2)	0.062 (2)	0.0150 (19)	0.0074 (18)	0.0345 (19)
C6B	0.062 (2)	0.069 (2)	0.054 (2)	0.022 (2)	0.0048 (17)	0.0260 (18)
C7B	0.091 (3)	0.098 (3)	0.078 (3)	0.017 (3)	0.001 (2)	0.055 (3)
C8B	0.068 (3)	0.083 (3)	0.086 (3)	0.005 (2)	0.018 (2)	0.043 (2)
Br1C	0.1027 (4)	0.0917 (3)	0.0714 (3)	0.0022 (3)	−0.0193 (2)	0.0430 (2)
Br2C	0.0905 (3)	0.0816 (3)	0.0888 (3)	−0.0050 (2)	0.0015 (2)	0.0514 (2)
O1C	0.0701 (17)	0.0681 (16)	0.0683 (16)	−0.0005 (14)	0.0031 (13)	0.0344 (13)
O2C	0.0641 (17)	0.0800 (18)	0.0633 (15)	0.0076 (14)	−0.0029 (13)	0.0368 (13)
C1C	0.067 (2)	0.058 (2)	0.057 (2)	0.0122 (19)	0.0017 (18)	0.0249 (18)
C2C	0.058 (2)	0.058 (2)	0.062 (2)	0.0034 (18)	−0.0028 (18)	0.0213 (18)
C3C	0.061 (2)	0.053 (2)	0.057 (2)	0.0108 (18)	0.0065 (18)	0.0224 (17)
C4C	0.060 (2)	0.055 (2)	0.053 (2)	0.0146 (18)	0.0037 (17)	0.0204 (17)
C5C	0.055 (2)	0.053 (2)	0.064 (2)	0.0069 (17)	0.0008 (17)	0.0212 (17)
C6C	0.064 (2)	0.054 (2)	0.063 (2)	0.0103 (18)	0.0079 (19)	0.0270 (17)
C7C	0.076 (3)	0.061 (2)	0.085 (3)	−0.004 (2)	0.015 (2)	0.025 (2)
C8C	0.064 (3)	0.096 (3)	0.069 (2)	0.009 (2)	−0.010 (2)	0.035 (2)
Br1D	0.0746 (3)	0.0780 (3)	0.0734 (3)	−0.0069 (2)	0.0003 (2)	0.0236 (2)
Br2D	0.0798 (3)	0.1106 (4)	0.0657 (3)	0.0040 (3)	−0.0051 (2)	0.0437 (2)
O1D	0.086 (2)	0.0850 (19)	0.0561 (15)	−0.0008 (15)	−0.0084 (14)	0.0320 (14)
O2D	0.0746 (18)	0.0818 (18)	0.0661 (16)	−0.0087 (15)	−0.0006 (14)	0.0292 (14)
C1D	0.059 (2)	0.053 (2)	0.057 (2)	0.0097 (17)	0.0081 (17)	0.0160 (17)
C2D	0.067 (2)	0.053 (2)	0.060 (2)	0.0079 (19)	0.0086 (18)	0.0238 (17)
C3D	0.070 (3)	0.060 (2)	0.053 (2)	0.015 (2)	0.0076 (18)	0.0212 (18)
C4D	0.063 (2)	0.063 (2)	0.055 (2)	0.0074 (19)	0.0063 (18)	0.0189 (18)
C5D	0.065 (2)	0.065 (2)	0.059 (2)	0.0070 (19)	0.0103 (18)	0.0311 (18)
C6D	0.061 (2)	0.064 (2)	0.054 (2)	0.0149 (19)	0.0061 (18)	0.0210 (18)
C7D	0.121 (4)	0.093 (3)	0.060 (2)	0.000 (3)	−0.005 (2)	0.043 (2)
C8D	0.074 (3)	0.083 (3)	0.088 (3)	−0.004 (2)	0.008 (2)	0.035 (2)

Geometric parameters (Å, º)

Br1A—C1A	1.887 (3)	Br1C—C1C	1.881 (3)
Br2A—C6A	1.883 (4)	Br2C—C6C	1.899 (4)
O1A—C3A	1.369 (4)	O1C—C3C	1.361 (4)
O1A—C7A	1.429 (5)	O1C—C7C	1.434 (4)
O2A—C4A	1.356 (4)	O2C—C4C	1.355 (4)
O2A—C8A	1.431 (5)	O2C—C8C	1.428 (4)
C1A—C6A	1.373 (5)	C1C—C6C	1.363 (5)
C1A—C2A	1.388 (5)	C1C—C2C	1.395 (5)
C2A—C3A	1.362 (5)	C2C—C3C	1.366 (5)
C2A—H2A	0.9300	C2C—H2C	0.9300
C3A—C4A	1.405 (5)	C3C—C4C	1.398 (5)
C4A—C5A	1.371 (5)	C4C—C5C	1.383 (5)
C5A—C6A	1.384 (5)	C5C—C6C	1.389 (5)
C5A—H5A	0.9300	C5C—H5C	0.9300
C7A—H7AA	0.9600	C7C—H7CA	0.9600
C7A—H7AB	0.9600	C7C—H7CB	0.9600
C7A—H7AC	0.9600	C7C—H7CC	0.9600
C8A—H8AA	0.9600	C8C—H8CA	0.9600
C8A—H8AB	0.9600	C8C—H8CB	0.9600
C8A—H8AC	0.9600	C8C—H8CC	0.9600
Br1B—C1B	1.886 (4)	Br1D—C1D	1.893 (4)
Br2B—C6B	1.885 (3)	Br2D—C6D	1.889 (3)
O1B—C3B	1.352 (4)	O1D—C3D	1.369 (4)
O1B—C7B	1.442 (5)	O1D—C7D	1.423 (5)
O2B—C4B	1.355 (4)	O2D—C4D	1.358 (4)
O2B—C8B	1.431 (4)	O2D—C8D	1.420 (5)
C1B—C6B	1.379 (5)	C1D—C6D	1.370 (5)
C1B—C2B	1.389 (5)	C1D—C2D	1.386 (5)
C2B—C3B	1.376 (5)	C2D—C3D	1.362 (5)
C2B—H2B	0.9300	C2D—H2D	0.9300
C3B—C4B	1.410 (5)	C3D—C4D	1.401 (5)
C4B—C5B	1.365 (5)	C4D—C5D	1.369 (5)
C5B—C6B	1.383 (5)	C5D—C6D	1.394 (5)
C5B—H5B	0.9300	C5D—H5D	0.9300
C7B—H7BA	0.9600	C7D—H7DA	0.9600
C7B—H7BB	0.9600	C7D—H7DB	0.9600
C7B—H7BC	0.9600	C7D—H7DC	0.9600
C8B—H8BA	0.9600	C8D—H8DA	0.9600
C8B—H8BB	0.9600	C8D—H8DB	0.9600
C8B—H8BC	0.9600	C8D—H8DC	0.9600
C3A—O1A—C7A	117.0 (3)	C3C—O1C—C7C	116.9 (3)
C4A—O2A—C8A	117.1 (3)	C4C—O2C—C8C	117.4 (3)
C6A—C1A—C2A	119.9 (3)	C6C—C1C—C2C	119.4 (3)
C6A—C1A—Br1A	121.9 (3)	C6C—C1C—Br1C	122.7 (3)
C2A—C1A—Br1A	118.2 (3)	C2C—C1C—Br1C	117.9 (3)
C3A—C2A—C1A	120.9 (4)	C3C—C2C—C1C	120.6 (3)
C3A—C2A—H2A	119.5	C3C—C2C—H2C	119.7
C1A—C2A—H2A	119.5	C1C—C2C—H2C	119.7
C2A—C3A—O1A	126.0 (4)	O1C—C3C—C2C	124.8 (3)
C2A—C3A—C4A	119.3 (4)	O1C—C3C—C4C	115.2 (3)
O1A—C3A—C4A	114.7 (3)	C2C—C3C—C4C	120.0 (3)
O2A—C4A—C5A	125.1 (4)	O2C—C4C—C5C	124.5 (3)
O2A—C4A—C3A	115.4 (3)	O2C—C4C—C3C	116.0 (3)
C5A—C4A—C3A	119.5 (3)	C5C—C4C—C3C	119.5 (3)
C4A—C5A—C6A	120.8 (4)	C4C—C5C—C6C	119.7 (3)
C4A—C5A—H5A	119.6	C4C—C5C—H5C	120.1
C6A—C5A—H5A	119.6	C6C—C5C—H5C	120.1
C1A—C6A—C5A	119.5 (4)	C1C—C6C—C5C	120.9 (3)
C1A—C6A—Br2A	122.4 (3)	C1C—C6C—Br2C	121.9 (3)
C5A—C6A—Br2A	118.1 (3)	C5C—C6C—Br2C	117.3 (3)
O1A—C7A—H7AA	109.5	O1C—C7C—H7CA	109.5
O1A—C7A—H7AB	109.5	O1C—C7C—H7CB	109.5
H7AA—C7A—H7AB	109.5	H7CA—C7C—H7CB	109.5
O1A—C7A—H7AC	109.5	O1C—C7C—H7CC	109.5
H7AA—C7A—H7AC	109.5	H7CA—C7C—H7CC	109.5
H7AB—C7A—H7AC	109.5	H7CB—C7C—H7CC	109.5
O2A—C8A—H8AA	109.5	O2C—C8C—H8CA	109.5
O2A—C8A—H8AB	109.5	O2C—C8C—H8CB	109.5
H8AA—C8A—H8AB	109.5	H8CA—C8C—H8CB	109.5
O2A—C8A—H8AC	109.5	O2C—C8C—H8CC	109.5
H8AA—C8A—H8AC	109.5	H8CA—C8C—H8CC	109.5
H8AB—C8A—H8AC	109.5	H8CB—C8C—H8CC	109.5
C3B—O1B—C7B	116.7 (3)	C3D—O1D—C7D	116.8 (3)
C4B—O2B—C8B	117.4 (3)	C4D—O2D—C8D	117.8 (3)
C6B—C1B—C2B	119.5 (3)	C6D—C1D—C2D	119.9 (3)
C6B—C1B—Br1B	122.4 (3)	C6D—C1D—Br1D	122.7 (3)
C2B—C1B—Br1B	118.1 (3)	C2D—C1D—Br1D	117.4 (3)
C3B—C2B—C1B	120.9 (3)	C3D—C2D—C1D	120.1 (3)
C3B—C2B—H2B	119.6	C3D—C2D—H2D	119.9
C1B—C2B—H2B	119.6	C1D—C2D—H2D	119.9
O1B—C3B—C2B	125.0 (3)	C2D—C3D—O1D	124.7 (3)
O1B—C3B—C4B	115.8 (3)	C2D—C3D—C4D	120.7 (3)
C2B—C3B—C4B	119.2 (3)	O1D—C3D—C4D	114.6 (3)
O2B—C4B—C5B	125.2 (3)	O2D—C4D—C5D	125.5 (4)
O2B—C4B—C3B	115.4 (3)	O2D—C4D—C3D	115.6 (3)
C5B—C4B—C3B	119.4 (3)	C5D—C4D—C3D	118.9 (3)
C4B—C5B—C6B	121.1 (3)	C4D—C5D—C6D	120.4 (3)
C4B—C5B—H5B	119.4	C4D—C5D—H5D	119.8
C6B—C5B—H5B	119.4	C6D—C5D—H5D	119.8
C1B—C6B—C5B	119.9 (3)	C1D—C6D—C5D	120.0 (3)
C1B—C6B—Br2B	122.0 (3)	C1D—C6D—Br2D	121.9 (3)
C5B—C6B—Br2B	118.1 (3)	C5D—C6D—Br2D	118.0 (3)
O1B—C7B—H7BA	109.5	O1D—C7D—H7DA	109.5
O1B—C7B—H7BB	109.5	O1D—C7D—H7DB	109.5
H7BA—C7B—H7BB	109.5	H7DA—C7D—H7DB	109.5
O1B—C7B—H7BC	109.5	O1D—C7D—H7DC	109.5
H7BA—C7B—H7BC	109.5	H7DA—C7D—H7DC	109.5
H7BB—C7B—H7BC	109.5	H7DB—C7D—H7DC	109.5
O2B—C8B—H8BA	109.5	O2D—C8D—H8DA	109.5
O2B—C8B—H8BB	109.5	O2D—C8D—H8DB	109.5
H8BA—C8B—H8BB	109.5	H8DA—C8D—H8DB	109.5
O2B—C8B—H8BC	109.5	O2D—C8D—H8DC	109.5
H8BA—C8B—H8BC	109.5	H8DA—C8D—H8DC	109.5
H8BB—C8B—H8BC	109.5	H8DB—C8D—H8DC	109.5

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C7A—H7AA···O2C^i	0.96	2.56	3.498 (5)	167
C8D—H8DA···O1B^ii	0.96	2.53	3.485 (5)	171

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

(II) 1,2-Diiodo-4,5-dimethoxybenzene

Crystal data

C8H8I2O2	Dx = 2.514 Mg m^−3
Mr = 389.94	Melting point: 404(1) K
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 25 reflections
a = 8.993 (4) Å	θ = 7.5–17.5°
b = 13.882 (9) Å	µ = 6.07 mm^−1
c = 16.506 (4) Å	T = 294 K
V = 2060.7 (17) Å^3	Blocks, colourless
Z = 8	0.32 × 0.26 × 0.16 mm
F(000) = 1424

Data collection

Rigaku AFC6 difractometer diffractometer	1441 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.039
Graphite monochromator	θmax = 26.0°, θmin = 2.5°
ω/2θ scans	h = −1→11
Absorption correction: ψ scan (North et al., 1968)	k = −1→17
Tmin = 0.18, Tmax = 0.38	l = −1→20
2652 measured reflections	3 standard reflections every 150 reflections
2023 independent reflections	intensity decay: <2%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.042	H-atom parameters constrained
wR(F^2) = 0.108	w = 1/[σ^2(Fo^2) + (0.0345P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.41	(Δ/σ)max = 0.001
2023 reflections	Δρmax = 0.82 e Å^−3
112 parameters	Δρmin = −0.76 e Å^−3
0 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0159 (6)

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
I1	0.08039 (8)	0.74558 (4)	0.55011 (4)	0.0553 (3)
I2	0.31872 (6)	0.53741 (4)	0.59939 (3)	0.0433 (2)
O1	−0.0021 (6)	0.5609 (4)	0.2648 (3)	0.0420 (13)
O2	0.1706 (6)	0.4178 (4)	0.2970 (3)	0.0437 (13)
C1	0.1135 (8)	0.6290 (5)	0.4722 (4)	0.0305 (16)
C2	0.0389 (8)	0.6337 (5)	0.3974 (4)	0.0343 (16)
H2	−0.0246	0.6849	0.3862	0.041*
C3	0.0605 (7)	0.5616 (6)	0.3403 (4)	0.0334 (16)
C4	0.1547 (8)	0.4835 (5)	0.3572 (4)	0.0305 (16)
C5	0.2286 (8)	0.4803 (5)	0.4318 (4)	0.0334 (17)
H5	0.2928	0.4295	0.4431	0.040*
C6	0.2070 (8)	0.5521 (6)	0.4891 (4)	0.0342 (17)
C7	−0.0979 (9)	0.6405 (6)	0.2433 (5)	0.049 (2)
H7A	−0.1316	0.6326	0.1885	0.074*
H7B	−0.0436	0.6998	0.2479	0.074*
H7C	−0.1819	0.6419	0.2791	0.074*
C8	0.2883 (10)	0.3511 (6)	0.3043 (5)	0.049 (2)
H8A	0.2903	0.3101	0.2575	0.073*
H8B	0.2738	0.3126	0.3520	0.073*
H8C	0.3809	0.3851	0.3085	0.073*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.0778 (5)	0.0460 (4)	0.0419 (4)	0.0067 (3)	0.0007 (3)	−0.0115 (3)
I2	0.0490 (4)	0.0532 (4)	0.0277 (3)	−0.0079 (3)	−0.0105 (2)	0.0019 (2)
O1	0.044 (3)	0.053 (3)	0.028 (2)	0.004 (3)	−0.008 (2)	0.004 (2)
O2	0.052 (3)	0.050 (3)	0.029 (3)	0.008 (3)	−0.006 (2)	−0.012 (3)
C1	0.030 (4)	0.030 (3)	0.032 (4)	−0.007 (3)	0.001 (3)	0.001 (3)
C2	0.033 (4)	0.036 (4)	0.033 (4)	0.005 (3)	0.003 (3)	−0.001 (3)
C3	0.027 (3)	0.051 (4)	0.022 (3)	−0.008 (3)	0.004 (3)	0.007 (3)
C4	0.035 (4)	0.032 (4)	0.025 (3)	−0.002 (3)	0.002 (3)	0.004 (3)
C5	0.037 (4)	0.038 (4)	0.025 (4)	0.003 (3)	−0.004 (3)	−0.002 (3)
C6	0.039 (4)	0.044 (4)	0.020 (3)	−0.009 (3)	0.003 (3)	0.003 (3)
C7	0.046 (5)	0.055 (5)	0.047 (5)	−0.011 (4)	−0.011 (4)	0.016 (4)
C8	0.058 (5)	0.046 (5)	0.043 (4)	0.014 (4)	−0.001 (4)	−0.010 (4)

Geometric parameters (Å, º)

I1—C1	2.089 (7)	C3—C4	1.404 (10)
I2—C6	2.090 (7)	C4—C5	1.401 (10)
O1—C3	1.366 (8)	C5—C6	1.387 (11)
O1—C7	1.446 (10)	C5—H5	0.9300
O2—C4	1.356 (9)	C7—H7A	0.9600
O2—C8	1.412 (9)	C7—H7B	0.9600
C1—C6	1.387 (10)	C7—H7C	0.9600
C1—C2	1.408 (10)	C8—H8A	0.9600
C2—C3	1.389 (10)	C8—H8B	0.9600
C2—H2	0.9300	C8—H8C	0.9600
C3—O1—C7	117.7 (6)	C4—C5—H5	119.7
C4—O2—C8	117.2 (6)	C1—C6—C5	120.1 (7)
C6—C1—C2	120.1 (6)	C1—C6—I2	122.7 (5)
C6—C1—I1	124.0 (5)	C5—C6—I2	117.1 (5)
C2—C1—I1	115.8 (5)	O1—C7—H7A	109.5
C3—C2—C1	119.7 (6)	O1—C7—H7B	109.5
C3—C2—H2	120.2	H7A—C7—H7B	109.5
C1—C2—H2	120.2	O1—C7—H7C	109.5
O1—C3—C2	124.5 (7)	H7A—C7—H7C	109.5
O1—C3—C4	115.1 (6)	H7B—C7—H7C	109.5
C2—C3—C4	120.4 (6)	O2—C8—H8A	109.5
O2—C4—C5	124.9 (6)	O2—C8—H8B	109.5
O2—C4—C3	115.9 (6)	H8A—C8—H8B	109.5
C5—C4—C3	119.1 (6)	O2—C8—H8C	109.5
C6—C5—C4	120.6 (7)	H8A—C8—H8C	109.5
C6—C5—H5	119.7	H8B—C8—H8C	109.5

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C7—H7A···Cg1^i	0.96	2.90	3.747 (8)	147

Symmetry code: (i) x−1/2, y, −z+1/2.