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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.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803005269/ac6033sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536803005269/ac6033Isup2.hkl
Contains datablock I

CCDC reference: 209947

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








Comment top

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.

Experimental top

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).

Refinement top

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 top

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 top
[Figure 1] Fig. 1. The two independent C4H6Br2N2 molecules. Displacement ellipsoids are shown at the 50% probability level and H atoms are shown with arbitrary radii.
[Figure 2] Fig. 2. The ππ 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.
[Figure 3] Fig. 3. View showing the Br···N interactions.
4,5-Dibromo-1-methyl-1H-imidazole top
Crystal data top
C4H4Br2N2Z = 4
Mr = 239.91F(000) = 448
Triclinic, P1Dx = 2.426 Mg m3
Hall symbol: -P 1Melting point = 352–353 K
a = 7.449 (2) ÅMo Kα radiation, λ = 0.71073 Å
b = 7.537 (2) ÅCell parameters from 1490 reflections
c = 12.403 (3) Åθ = 2.8–27.4°
α = 73.47 (3)°µ = 12.23 mm1
β = 79.92 (3)°T = 174 K
γ = 85.45 (3)°Prism, colorless
V = 656.9 (3) Å30.20 × 0.15 × 0.07 mm
Data collection top
Siemens SMART area-detector
diffractometer
2962 independent reflections
Radiation source: fine-focus sealed tube2615 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.028
ω scansθmax = 27.5°, θmin = 1.7°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996; Blessing, 1995)
h = 99
Tmin = 0.12, Tmax = 0.42k = 99
6725 measured reflectionsl = 1615
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.032Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.080H-atom parameters constrained
S = 1.08 w = 1/[σ2(Fo2) + (0.037P)2 + 1.41P]
where P = (Fo2 + 2Fc2)/3
2962 reflections(Δ/σ)max = 0.001
147 parametersΔρmax = 0.82 e Å3
0 restraintsΔρmin = 0.72 e Å3
Crystal data top
C4H4Br2N2γ = 85.45 (3)°
Mr = 239.91V = 656.9 (3) Å3
Triclinic, P1Z = 4
a = 7.449 (2) ÅMo Kα radiation
b = 7.537 (2) ŵ = 12.23 mm1
c = 12.403 (3) ÅT = 174 K
α = 73.47 (3)°0.20 × 0.15 × 0.07 mm
β = 79.92 (3)°
Data collection top
Siemens SMART area-detector
diffractometer
2962 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996; Blessing, 1995)
2615 reflections with I > 2σ(I)
Tmin = 0.12, Tmax = 0.42Rint = 0.028
6725 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0320 restraints
wR(F2) = 0.080H-atom parameters constrained
S = 1.08Δρmax = 0.82 e Å3
2962 reflectionsΔρmin = 0.72 e Å3
147 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Br10.58550 (5)0.26614 (6)0.67042 (3)0.02692 (11)
Br20.10229 (6)0.23264 (6)0.65183 (4)0.03028 (12)
N110.2901 (5)0.2094 (5)0.4351 (3)0.0277 (7)
C120.4612 (6)0.2122 (5)0.3815 (3)0.0260 (8)
H12A0.49480.20130.30610.031*
N130.5836 (5)0.2327 (5)0.4474 (3)0.0244 (7)
C140.4808 (6)0.2445 (5)0.5493 (3)0.0228 (8)
C150.3052 (5)0.2304 (5)0.5391 (3)0.0234 (8)
C160.7804 (6)0.2382 (6)0.4169 (4)0.0322 (9)
H16A0.82190.35610.42090.048*
H16B0.81610.22670.33930.048*
H16C0.83640.13570.47010.048*
Br30.28089 (6)0.44139 (6)0.11411 (4)0.03273 (12)
Br40.29293 (7)0.91005 (6)0.07735 (4)0.03893 (13)
N210.2079 (5)0.6770 (5)0.1483 (3)0.0283 (7)
C220.1827 (6)0.4986 (6)0.1994 (3)0.0276 (9)
H22A0.15420.44890.27960.033*
N230.2018 (4)0.3953 (5)0.1250 (3)0.0234 (7)
C240.2406 (5)0.5179 (6)0.0178 (3)0.0230 (8)
C250.2437 (5)0.6864 (5)0.0354 (3)0.0231 (8)
C260.1784 (7)0.1957 (6)0.1535 (4)0.0349 (10)
H26A0.16290.14340.23640.052*
H26B0.28630.13790.11790.052*
H26C0.07020.17190.12530.052*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br10.0284 (2)0.0304 (2)0.0254 (2)0.00208 (16)0.00528 (15)0.01238 (16)
Br20.0248 (2)0.0292 (2)0.0349 (2)0.00051 (16)0.00117 (16)0.00930 (17)
N110.0347 (19)0.0222 (17)0.0258 (17)0.0015 (14)0.0086 (15)0.0037 (14)
C120.035 (2)0.0203 (19)0.0225 (19)0.0027 (16)0.0046 (16)0.0047 (15)
N130.0286 (17)0.0218 (17)0.0217 (16)0.0017 (13)0.0009 (13)0.0057 (13)
C140.033 (2)0.0170 (18)0.0193 (18)0.0004 (15)0.0051 (15)0.0053 (14)
C150.028 (2)0.0166 (18)0.0234 (19)0.0005 (15)0.0019 (16)0.0037 (14)
C160.030 (2)0.033 (2)0.032 (2)0.0029 (18)0.0041 (17)0.0101 (18)
Br30.0467 (3)0.0307 (2)0.0233 (2)0.00102 (18)0.00348 (17)0.01320 (16)
Br40.0574 (3)0.0240 (2)0.0336 (2)0.0085 (2)0.0060 (2)0.00373 (17)
N210.0327 (19)0.0316 (19)0.0237 (17)0.0012 (15)0.0067 (14)0.0113 (14)
C220.027 (2)0.038 (2)0.0197 (19)0.0040 (17)0.0054 (15)0.0112 (17)
N230.0229 (16)0.0220 (17)0.0239 (17)0.0005 (13)0.0032 (13)0.0051 (13)
C240.0224 (18)0.026 (2)0.0212 (18)0.0019 (15)0.0021 (14)0.0081 (15)
C250.0262 (19)0.0229 (19)0.0201 (18)0.0008 (15)0.0036 (15)0.0060 (15)
C260.044 (3)0.022 (2)0.035 (2)0.0019 (18)0.004 (2)0.0045 (17)
Geometric parameters (Å, º) top
Br1—C141.860 (4)Br3—C241.854 (4)
Br2—C151.873 (4)Br4—C251.873 (4)
N11—C121.329 (6)N21—C221.326 (6)
N11—C151.369 (5)N21—C251.361 (5)
C12—N131.370 (5)C22—N231.350 (5)
C12—H12A0.9500C22—H22A0.9500
N13—C141.381 (5)N23—C241.383 (5)
N13—C161.450 (5)N23—C261.461 (5)
C14—C151.352 (6)C24—C251.351 (6)
C16—H16A0.9800C26—H26A0.9800
C16—H16B0.9800C26—H26B0.9800
C16—H16C0.9800C26—H26C0.9800
C12—N11—C15104.1 (3)C22—N21—C25104.1 (3)
N11—C12—N13112.3 (4)N21—C22—N23112.7 (4)
N11—C12—H12A123.8N21—C22—H22A123.6
N13—C12—H12A123.8N23—C22—H22A123.6
C12—N13—C14105.8 (3)C22—N23—C24105.9 (3)
C12—N13—C16127.1 (4)C22—N23—C26126.3 (4)
C14—N13—C16127.1 (4)C24—N23—C26127.7 (4)
C15—C14—N13106.0 (3)C25—C24—N23105.7 (3)
C15—C14—Br1131.4 (3)C25—C24—Br3131.9 (3)
N13—C14—Br1122.5 (3)N23—C24—Br3122.4 (3)
C14—C15—N11111.8 (4)C24—C25—N21111.6 (4)
C14—C15—Br2125.8 (3)C24—C25—Br4126.2 (3)
N11—C15—Br2122.4 (3)N21—C25—Br4122.2 (3)
N13—C16—H16A109.5N23—C26—H26A109.5
N13—C16—H16B109.5N23—C26—H26B109.5
H16A—C16—H16B109.5H26A—C26—H26B109.5
N13—C16—H16C109.5N23—C26—H26C109.5
H16A—C16—H16C109.5H26A—C26—H26C109.5
H16B—C16—H16C109.5H26B—C26—H26C109.5

Experimental details

Crystal data
Chemical formulaC4H4Br2N2
Mr239.91
Crystal system, space groupTriclinic, P1
Temperature (K)174
a, b, c (Å)7.449 (2), 7.537 (2), 12.403 (3)
α, β, γ (°)73.47 (3), 79.92 (3), 85.45 (3)
V3)656.9 (3)
Z4
Radiation typeMo Kα
µ (mm1)12.23
Crystal size (mm)0.20 × 0.15 × 0.07
Data collection
DiffractometerSiemens SMART area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996; Blessing, 1995)
Tmin, Tmax0.12, 0.42
No. of measured, independent and
observed [I > 2σ(I)] reflections
6725, 2962, 2615
Rint0.028
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.032, 0.080, 1.08
No. of reflections2962
No. of parameters147
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.82, 0.72

Computer programs: SMART (Siemens, 1995), SAINT (Siemens, 1995), SAINT, SHELXTL (Sheldrick, 1997), SHELXTL.

Distances and angles (Å, °) in the C—X···Y—C contacts top
XYC—HC—X···YX···YX···Y—CC(H)···X
H16ABr2i0.981583.04823.969 (4)
H26BBr4ii0.981483.10983.958 (4)
H26CBr4iii0.981713.02803.986 (4)
H16CN11iv0.981272.701143.383 (5)
Br1N21i-173.93.078 (4)94.2,137.5-
Br2N21v-166.53.264 (4)87.9,143.6-
Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii) 1 − x, 1 − y, −z; (iii) −x, 1 − y, −z; (iv) 1 − x, −y, 1 − z; (v) −x, 1 − y, 1 − z.
 

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