4,5-Di­bromo-1-methyl-1H-imidazole

The title compound, C₄H₄Br₂N₂, crystallizes with two mol­ecules in the asymmetric unit. Each mol­ecule forms stacks with its own kind, the stacks being approximately orthogonal to each other. Both Br atoms in mol­ecule 1 form Lewis acid–base interactions with N atoms in mol­ecule 2, with Br...N distances of 3.078 (4) and 3.264 (4) Å.

Key indicators

• Single-crystal X-ray study
• T = 174 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.032
• wR factor = 0.080
• Data-to-parameter ratio = 20.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

---

S1. Comment

In the course of work intended to continue a study of copper(I) cyanide complexes with imidazoles (Stocker et al., 2000), we have determined the structure of the title compound, (I).

There are two molecules in the asymmetric unit. The anisotropic displacement ellipsoids and atom labelling are shown in Fig. 1. The bond lengths and angles agree between the two molecules, within experimental error. They also agree with the values in unsubstituted imidazole (Craven et al., 1977).

Both independent molecules form stacks with their own kind. Views down the stacks are shown in Fig. 2. The stacks of molecule 1 are parallel to the b axis, those of molelcule 2 are parallel to the a axis.

In both stacks, adjacent molecules are related by inversion centers. In stack 1, the upper molecule and the central one each have a Br atom above or below the ring in the next molecule at the perpendicular distance of 3.655 (2) Å. The lower and central molecules have the rings overlapping at a distance of 3.285 (2) Å. In stack 2, the overlaps on both sides are similar to the Br–ring overlaps in stack 1, with distances of 3.626 (2) and 3.754 (2) Å. In each of the three Br–ring overlaps, there are intermoleculular H···Br contacts of 3.10 Å or less. The metric details are given in Table 1.

Just as the two stacks are significantly different, the interactions between the two kinds of stacks are also significantly different. There is a C—H···N interaction between molecules in adjacent stacks of molecule 1, but no similar interaction bewteen stacks of molecule 2. Both Br atoms in molecule 1 interact with ring N atoms in molecule 2 with short Br···N distances (see Fig. 3). There are no Br···N interactions involving the Br atoms on molecule 2. There are also no Br···Br contacts closer than 3.6 Å in the entire structure. The metric details of the interactions are given in Table 1.

S2. Experimental

The title compound has been prepared previously by dibromination of 1-methyl-1H-imidazole with bromine in chloroform at 278–283 K in 0.5% yield (as the picrate; along with 13% of the 2,4,5-tribromo compound; Balaban & Pyman, 1924), or with N-bromosuccinimide in refluxing CHCl₃ in 25–40% yield (Borai et al., 1981). We used a modification of the latter procedure, with N-bromosuccinimide in CH₂Cl₂. Addition of 3 drops of hydrogen peroxide and irradiation with a tungsten lamp produced a vigorous exothermic reaction, with foaming, which gave the desired product as colorless needles, m.p. 352–353 K; literature: colorless, m.p. 351–352 (Sonn et al., 1924), 352–353 (Balaban & Pyman, 1924), 353 (Borai et al., 1981), 353–354 (Boulton & Coller, 1974), 354 K (Katritzky et al., 1989); IR (KBr) cm ⁻¹ 3110 (w) and 3092 (w, 2-CH), 2943 (w, 1-CH₃), 1490 (s), 1248 (ms), 1101 (ms), 958 (s); ¹H NMR (CDCl₃): δ 7.45 (s, 0.8H, 2-H), 3.62 (s, 3H, 1-CH₃); ¹³C NMR (CDCl₃): δ 137.5 (2-CH), 116.8 (5-C), 104.4(4-C), 34.1 (1-CH₃). The literature ¹H NMR (Borai et al., 1981; Boulton & Coller, 1974; Katritzky et al., 1989; O'Connell et al., 1988) and ¹³C NMR (Katritzky et al., 1989) data are in reasonable agreement with those for (I).

S3. Refinement

All of the peaks higher than 0.4 e Å⁻³ in the final difference Fourier map lie about 1 Å from a Br atom. The methyl H atoms were included at idealized positions with the methyl groups allowed to rotate around the C—C bonds.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The two independent C4H6Br2N2 molecules. Displacement ellipsoids are shown at the 50% probability level and H atoms are shown with arbitrary radii.
	Fig. 2. The π–π overlap between the molecules, viewed normal to the plane of the molecules. Left: molecule 1; right: molecule 2. The solid bonds define the central molecule in each case, the open bonds the molecule above, the dashed bonds the molecule below. The dashed lines show the H···Br contacts at 3.1 Å or less.
	Fig. 3. View showing the Br···N interactions.

4,5-Dibromo-1-methyl-1H-imidazole

Crystal data

C4H4Br2N2	Z = 4
Mr = 239.91	F(000) = 448
Triclinic, P1	Dx = 2.426 Mg m^−3
Hall symbol: -P 1	Melting point = 352–353 K
a = 7.449 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.537 (2) Å	Cell parameters from 1490 reflections
c = 12.403 (3) Å	θ = 2.8–27.4°
α = 73.47 (3)°	µ = 12.23 mm^−1
β = 79.92 (3)°	T = 174 K
γ = 85.45 (3)°	Prism, colorless
V = 656.9 (3) Å^3	0.20 × 0.15 × 0.07 mm

Data collection

Siemens SMART area-detector diffractometer	2962 independent reflections
Radiation source: fine-focus sealed tube	2615 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
ω scans	θmax = 27.5°, θmin = 1.7°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996; Blessing, 1995)	h = −9→9
Tmin = 0.12, Tmax = 0.42	k = −9→9
6725 measured reflections	l = −16→15

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)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.080	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.037P)^2 + 1.41P] where P = (Fo^2 + 2Fc^2)/3
2962 reflections	(Δ/σ)max = 0.001
147 parameters	Δρmax = 0.82 e Å^−3
0 restraints	Δρmin = −0.72 e Å^−3

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

	x	y	z	Uiso*/Ueq
Br1	0.58550 (5)	0.26614 (6)	0.67042 (3)	0.02692 (11)
Br2	0.10229 (6)	0.23264 (6)	0.65183 (4)	0.03028 (12)
N11	0.2901 (5)	0.2094 (5)	0.4351 (3)	0.0277 (7)
C12	0.4612 (6)	0.2122 (5)	0.3815 (3)	0.0260 (8)
H12A	0.4948	0.2013	0.3061	0.031*
N13	0.5836 (5)	0.2327 (5)	0.4474 (3)	0.0244 (7)
C14	0.4808 (6)	0.2445 (5)	0.5493 (3)	0.0228 (8)
C15	0.3052 (5)	0.2304 (5)	0.5391 (3)	0.0234 (8)
C16	0.7804 (6)	0.2382 (6)	0.4169 (4)	0.0322 (9)
H16A	0.8219	0.3561	0.4209	0.048*
H16B	0.8161	0.2267	0.3393	0.048*
H16C	0.8364	0.1357	0.4701	0.048*
Br3	0.28089 (6)	0.44139 (6)	−0.11411 (4)	0.03273 (12)
Br4	0.29293 (7)	0.91005 (6)	−0.07735 (4)	0.03893 (13)
N21	0.2079 (5)	0.6770 (5)	0.1483 (3)	0.0283 (7)
C22	0.1827 (6)	0.4986 (6)	0.1994 (3)	0.0276 (9)
H22A	0.1542	0.4489	0.2796	0.033*
N23	0.2018 (4)	0.3953 (5)	0.1250 (3)	0.0234 (7)
C24	0.2406 (5)	0.5179 (6)	0.0178 (3)	0.0230 (8)
C25	0.2437 (5)	0.6864 (5)	0.0354 (3)	0.0231 (8)
C26	0.1784 (7)	0.1957 (6)	0.1535 (4)	0.0349 (10)
H26A	0.1629	0.1434	0.2364	0.052*
H26B	0.2863	0.1379	0.1179	0.052*
H26C	0.0702	0.1719	0.1253	0.052*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0284 (2)	0.0304 (2)	0.0254 (2)	−0.00208 (16)	−0.00528 (15)	−0.01238 (16)
Br2	0.0248 (2)	0.0292 (2)	0.0349 (2)	−0.00051 (16)	0.00117 (16)	−0.00930 (17)
N11	0.0347 (19)	0.0222 (17)	0.0258 (17)	−0.0015 (14)	−0.0086 (15)	−0.0037 (14)
C12	0.035 (2)	0.0203 (19)	0.0225 (19)	−0.0027 (16)	−0.0046 (16)	−0.0047 (15)
N13	0.0286 (17)	0.0218 (17)	0.0217 (16)	−0.0017 (13)	−0.0009 (13)	−0.0057 (13)
C14	0.033 (2)	0.0170 (18)	0.0193 (18)	−0.0004 (15)	−0.0051 (15)	−0.0053 (14)
C15	0.028 (2)	0.0166 (18)	0.0234 (19)	−0.0005 (15)	−0.0019 (16)	−0.0037 (14)
C16	0.030 (2)	0.033 (2)	0.032 (2)	−0.0029 (18)	0.0041 (17)	−0.0101 (18)
Br3	0.0467 (3)	0.0307 (2)	0.0233 (2)	0.00102 (18)	−0.00348 (17)	−0.01320 (16)
Br4	0.0574 (3)	0.0240 (2)	0.0336 (2)	−0.0085 (2)	−0.0060 (2)	−0.00373 (17)
N21	0.0327 (19)	0.0316 (19)	0.0237 (17)	−0.0012 (15)	−0.0067 (14)	−0.0113 (14)
C22	0.027 (2)	0.038 (2)	0.0197 (19)	0.0040 (17)	−0.0054 (15)	−0.0112 (17)
N23	0.0229 (16)	0.0220 (17)	0.0239 (17)	0.0005 (13)	−0.0032 (13)	−0.0051 (13)
C24	0.0224 (18)	0.026 (2)	0.0212 (18)	−0.0019 (15)	−0.0021 (14)	−0.0081 (15)
C25	0.0262 (19)	0.0229 (19)	0.0201 (18)	−0.0008 (15)	−0.0036 (15)	−0.0060 (15)
C26	0.044 (3)	0.022 (2)	0.035 (2)	−0.0019 (18)	−0.004 (2)	−0.0045 (17)

Geometric parameters (Å, º)

Br1—C14	1.860 (4)	Br3—C24	1.854 (4)
Br2—C15	1.873 (4)	Br4—C25	1.873 (4)
N11—C12	1.329 (6)	N21—C22	1.326 (6)
N11—C15	1.369 (5)	N21—C25	1.361 (5)
C12—N13	1.370 (5)	C22—N23	1.350 (5)
C12—H12A	0.9500	C22—H22A	0.9500
N13—C14	1.381 (5)	N23—C24	1.383 (5)
N13—C16	1.450 (5)	N23—C26	1.461 (5)
C14—C15	1.352 (6)	C24—C25	1.351 (6)
C16—H16A	0.9800	C26—H26A	0.9800
C16—H16B	0.9800	C26—H26B	0.9800
C16—H16C	0.9800	C26—H26C	0.9800
C12—N11—C15	104.1 (3)	C22—N21—C25	104.1 (3)
N11—C12—N13	112.3 (4)	N21—C22—N23	112.7 (4)
N11—C12—H12A	123.8	N21—C22—H22A	123.6
N13—C12—H12A	123.8	N23—C22—H22A	123.6
C12—N13—C14	105.8 (3)	C22—N23—C24	105.9 (3)
C12—N13—C16	127.1 (4)	C22—N23—C26	126.3 (4)
C14—N13—C16	127.1 (4)	C24—N23—C26	127.7 (4)
C15—C14—N13	106.0 (3)	C25—C24—N23	105.7 (3)
C15—C14—Br1	131.4 (3)	C25—C24—Br3	131.9 (3)
N13—C14—Br1	122.5 (3)	N23—C24—Br3	122.4 (3)
C14—C15—N11	111.8 (4)	C24—C25—N21	111.6 (4)
C14—C15—Br2	125.8 (3)	C24—C25—Br4	126.2 (3)
N11—C15—Br2	122.4 (3)	N21—C25—Br4	122.2 (3)
N13—C16—H16A	109.5	N23—C26—H26A	109.5
N13—C16—H16B	109.5	N23—C26—H26B	109.5
H16A—C16—H16B	109.5	H26A—C26—H26B	109.5
N13—C16—H16C	109.5	N23—C26—H26C	109.5
H16A—C16—H16C	109.5	H26A—C26—H26C	109.5
H16B—C16—H16C	109.5	H26B—C26—H26C	109.5