Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270111008742/gd3380sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270111008742/gd3380Isup2.hkl |
CCDC reference: 824043
The title compound was synthesized by bromination of p-xylene and recrystallized by slow evaporation from acetone.
Methyl H atoms were identified in difference syntheses and idealized (C—H = 0.98 Å and H—C—H = 109.5 °). The methyl group was refined as a rigid group allowed to rotate but not tip. Aromatic H atoms were introduced at calculated positions and refined using a riding model, with C—H = 0.95 Å. The Uiso(H) values were set equal to mUeq(C), with m = 1.2 for aromatic and 1.5 for methyl H atoms.
Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP (Siemens, 1994); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).
C8H8Br2 | F(000) = 252 |
Mr = 263.96 | Dx = 2.100 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 5832 reflections |
a = 6.2597 (6) Å | θ = 3.2–30.5° |
b = 10.4820 (11) Å | µ = 9.63 mm−1 |
c = 6.4281 (6) Å | T = 133 K |
β = 98.134 (4)° | Irregular, colourless |
V = 417.53 (7) Å3 | 0.20 × 0.15 × 0.12 mm |
Z = 2 |
Bruker SMART 1000 CCD area-detector diffractometer | 1269 independent reflections |
Radiation source: fine-focus sealed tube | 1214 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.021 |
Detector resolution: 8.192 pixels mm-1 | θmax = 30.5°, θmin = 3.8° |
ϕ and ω scans | h = −8→8 |
Absorption correction: multi-scan (SADABS; Bruker, 1998) | k = −14→14 |
Tmin = 0.292, Tmax = 0.391 | l = −9→9 |
7909 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.019 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.051 | H-atom parameters constrained |
S = 1.13 | w = 1/[σ2(Fo2) + (0.0241P)2 + 0.4037P] where P = (Fo2 + 2Fc2)/3 |
1269 reflections | (Δ/σ)max = 0.001 |
47 parameters | Δρmax = 0.63 e Å−3 |
0 restraints | Δρmin = −0.46 e Å−3 |
C8H8Br2 | V = 417.53 (7) Å3 |
Mr = 263.96 | Z = 2 |
Monoclinic, P21/n | Mo Kα radiation |
a = 6.2597 (6) Å | µ = 9.63 mm−1 |
b = 10.4820 (11) Å | T = 133 K |
c = 6.4281 (6) Å | 0.20 × 0.15 × 0.12 mm |
β = 98.134 (4)° |
Bruker SMART 1000 CCD area-detector diffractometer | 1269 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 1998) | 1214 reflections with I > 2σ(I) |
Tmin = 0.292, Tmax = 0.391 | Rint = 0.021 |
7909 measured reflections |
R[F2 > 2σ(F2)] = 0.019 | 0 restraints |
wR(F2) = 0.051 | H-atom parameters constrained |
S = 1.13 | Δρmax = 0.63 e Å−3 |
1269 reflections | Δρmin = −0.46 e Å−3 |
47 parameters |
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. Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane) 2.5962 (0.0041) x + 6.9385 (0.0034) y + 3.5958 (0.0046) z = 4.7762 (0.0019) * -0.0015 (0.0007) Br1 * 0.0011 (0.0011) C1 * 0.0036 (0.0014) C2 * -0.0026 (0.0008) C3 * -0.0006 (0.0005) C4 Rms deviation of fitted atoms = 0.0022 |
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 > σ(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. |
x | y | z | Uiso*/Ueq | ||
Br1 | 0.67598 (3) | 0.269096 (18) | 0.32055 (3) | 0.02107 (7) | |
C1 | 0.5701 (3) | 0.40421 (15) | 0.1370 (2) | 0.0147 (3) | |
C2 | 0.3763 (3) | 0.46429 (16) | 0.1617 (2) | 0.0147 (3) | |
C3 | 0.3091 (3) | 0.56219 (15) | 0.0196 (3) | 0.0152 (3) | |
H3 | 0.1787 | 0.6064 | 0.0304 | 0.018* | |
C4 | 0.2409 (3) | 0.42605 (17) | 0.3321 (3) | 0.0175 (3) | |
H4A | 0.1181 | 0.4844 | 0.3288 | 0.021* | |
H4B | 0.3300 | 0.4306 | 0.4701 | 0.021* | |
H4C | 0.1878 | 0.3387 | 0.3065 | 0.021* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Br1 | 0.02050 (10) | 0.02010 (11) | 0.02220 (11) | 0.00190 (6) | 0.00156 (7) | 0.00761 (6) |
C1 | 0.0157 (7) | 0.0131 (7) | 0.0148 (7) | −0.0005 (5) | 0.0002 (5) | 0.0014 (5) |
C2 | 0.0157 (7) | 0.0146 (7) | 0.0136 (6) | −0.0019 (6) | 0.0019 (5) | −0.0013 (5) |
C3 | 0.0142 (7) | 0.0148 (7) | 0.0166 (7) | 0.0001 (5) | 0.0025 (5) | −0.0015 (5) |
C4 | 0.0142 (7) | 0.0216 (8) | 0.0174 (7) | −0.0014 (6) | 0.0046 (5) | −0.0025 (6) |
Br1—C1 | 1.9016 (16) | C3—H3 | 0.9500 |
C1—C3i | 1.387 (2) | C4—H4A | 0.9800 |
C1—C2 | 1.396 (2) | C4—H4B | 0.9800 |
C2—C3 | 1.399 (2) | C4—H4C | 0.9800 |
C2—C4 | 1.530 (2) | ||
C3i—C1—C2 | 122.68 (15) | C2—C3—H3 | 119.5 |
C3i—C1—Br1 | 117.48 (12) | C2—C4—H4A | 109.5 |
C2—C1—Br1 | 119.84 (12) | C2—C4—H4B | 109.5 |
C1—C2—C3 | 116.27 (14) | H4A—C4—H4B | 109.5 |
C1—C2—C4 | 122.80 (14) | C2—C4—H4C | 109.5 |
C3—C2—C4 | 120.92 (15) | H4A—C4—H4C | 109.5 |
C1i—C3—C2 | 121.05 (15) | H4B—C4—H4C | 109.5 |
C1i—C3—H3 | 119.5 | ||
C3i—C1—C2—C3 | −0.4 (3) | Br1—C1—C2—C4 | −0.2 (2) |
Br1—C1—C2—C3 | −179.64 (12) | C1—C2—C3—C1i | 0.4 (3) |
C3i—C1—C2—C4 | 179.01 (15) | C4—C2—C3—C1i | −179.03 (15) |
Symmetry code: (i) −x+1, −y+1, −z. |
D—H···A | D—H | H···A | D···A | D—H···A |
C3—H3···Br1ii | 0.95 | 3.06 | 3.9829 (16) | 165 |
Symmetry code: (ii) −x+1/2, y+1/2, −z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C8H8Br2 |
Mr | 263.96 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 133 |
a, b, c (Å) | 6.2597 (6), 10.4820 (11), 6.4281 (6) |
β (°) | 98.134 (4) |
V (Å3) | 417.53 (7) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 9.63 |
Crystal size (mm) | 0.20 × 0.15 × 0.12 |
Data collection | |
Diffractometer | Bruker SMART 1000 CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 1998) |
Tmin, Tmax | 0.292, 0.391 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7909, 1269, 1214 |
Rint | 0.021 |
(sin θ/λ)max (Å−1) | 0.714 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.019, 0.051, 1.13 |
No. of reflections | 1269 |
No. of parameters | 47 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.63, −0.46 |
Computer programs: SMART (Bruker, 1998), SAINT (Bruker, 1998), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XP (Siemens, 1994).
C3i—C1—C2 | 122.68 (15) | C1i—C3—C2 | 121.05 (15) |
C1—C2—C3 | 116.27 (14) |
Symmetry code: (i) −x+1, −y+1, −z. |
D—H···A | D—H | H···A | D···A | D—H···A |
C3—H3···Br1ii | 0.95 | 3.06 | 3.9829 (16) | 164.7 |
Symmetry code: (ii) −x+1/2, y+1/2, −z+1/2. |
C—Br···Br—C system | Br···Br (Å) | C—Br···Br angles (°) | Symmetry code |
C1—Br1···Br1—C1 | 3.719 | 151 and 151 | -x, -y + 2, -z |
C4—Br2···Br1—C1 | 3.939 | 74 and 124 | -x + 1/2, y - 1/2, -z + 1/2 |
C4—Br2···Br1—C1 | 3.672 | 151 and 136 | x - 1/2, -y + 3/2, z + 1/2 |
We are interested in secondary interactions in brominated aromatic hydrocarbons [see, for example, our studies of all ten isomers of di(bromomethyl)naphthalenes; Jones & Kuś, 2010, and related references therein]. Such interactions may include `weak' C—H···Br hydrogen bonds, Br···Br halogen bonds, π–π stacking, and H···π and Br···π contacts. We are currently preparing a study of several benzene derivatives multiply substituted with bromo, methyl and bromomethyl groups. The title compound, (I), is being published separately because it is a known compound and its structure, as crystallised from ethanol, has already been determined in space group P21/n with Z = 4 [Reiter et al. (2005), hereinafter polymorph (Ia); refcode JAQJAN in the Cambridge Structural Database (Allen, 2002)]. However, in our hands the compound crystallized from acetone as a new polymorph in P21/n with Z = 2 and thus with imposed inversion symmetry, polymorph (Ib). We describe here the packing of both polymorphs, which are totally different from each other. The previous study described the packing of (Ia) in only general terms, but clearly recognized the presence of Br···Br contacts; the compound was a starting material (for the synthesis of p-xylylene-1,4-diphosphines) and thus the structure was only of peripheral interest.
The molecule of polymorph (Ib) is shown in Fig. 1. It has the same general features as the previous polymorph, (Ia), such as coplanarity of all non-H atoms (r.m.s. deviation = 0.002 Å) and deviations of endocyclic angles from the ideal 120° (slightly wider at atom C1 and slightly narrower at C2; Table 1).
The molecular packing of polymorph (Ib) is surprising. There are no interactions of the types H···π or π–π, and the shortest Br1···Br1 contact is 4.1761 (3) Å via symmetry operators (x + 1/2, -y + 1/2, z + 1/2) or (x - 1/2, -y + 1/2, z - 1/2); this distance would usually be considered too long for any significant interaction. There is one weak hydrogen bond of the type C—H···Br1 (Table 2) involving an aromatic H atom; the methyl H atoms play no significant role in the aggregation. The weakness of C—H···Br—C interactions has been commented on by Brammer et al. (2001). A search for contacts to the centre of gravity (Cg) of the ring reveals a Br1···Cg contact of 3.57 Å via the symmetry operator (x + 1/2, -y + 1/2, z + 1/2), but closer inspection shows that the interaction is better represented by Br1···(mid-point of C1—C2), with a distance of 3.37 Å and an angle at Br1 of 167°. The interaction is almost perpendicular (80°) to the ring plane. The Br1···Br1 contact mentioned above is therefore best seen as a consequence of the Br1···π interaction; if this is short, then the two Br atoms related by the same operator must also approach each other.
The combination of these two contacts with the inversion symmetry of the molecule leads to a three-dimensional packing, but the general features are easily recognisable, especially when depth-cued (Fig. 2).
The packing of the previously known polymorph (Ia) is conceptually much simpler. Apart from some rather nonlinear weak hydrogen bonds (C—Hmethyl···Br = 3.08 Å and angle = 136°; C—Har···Cg = 2.92 Å and angle = 133°; C—Hmethyl···Cg = 2.88 Å and angle = 134°), the main features are Br···Br interactions. The Br atoms occupy the regions z ≈ 0, 1/2, 1, etc., and the contacts link the molecules via chains of inversion-symmetric Br12Br22 trapezia parallel to the a axis, themselves connected by Br1···Br1 contacts (Fig. 3 and Table 3). The classification of Pedireddi et al. (1994) suggests that the two shorter contacts are type I in nature (approximately equal C—Br···Br angles), whereas the longest contact does not fit either of the two main types (type II, usually considered to represent stronger interactions, has one angle ca 90° and one ca 180°).
We have previously commented (Jones & Kuś, 2010) that it is difficult to predict or rationalize which type(s) of contacts will appear in the packing of any given brominated aromatic hydrocarbon. Our findings here lend weight to this view. The packing of the previously known polymorph (Ia) of compound (I) was largely determined by Br···Br interactions (as one might expect), but the new polymorph (Ib) features H···Br and Br···π contacts. The packing efficiency as judged by the density is slightly greater for polymorph (Ib) [2.100 Mg m-3 at 133 K, compared with 2.087 Mg m-3 at 143 K for polymorph (Ia)].