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The title compound, C8H12Br4, displays crystallographic inversion symmetry, so that the cyclo­butane ring is exactly planar. The ring C—C bond with eclipsed substituents is lengthened somewhat to 1.572 (5) Å. The packing can be described in terms of three Br...Br contacts; two of these combine to form layers of mol­ecules parallel to the ac plane, while the third crosslinks the layers in the third dimension. A simple topological descriptor for systems involving Br...Br contacts is proposed.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270113010597/gz3236sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270113010597/gz3236Isup2.hkl
Contains datablock I

CCDC reference: 950436

Comment top

1,2,3,4-Tetrakis(bromomethyl)cyclobutane, (I), is an important intermediate in the preparation of [4]radialene, (II) (Griffin & Peterson, 1962, 1963; Peterson et al., 1968; Bally et al., 1978; cf. Hopf & Trabert, 1980). Although it is likely, from the pathway of preparation of (I), that it has the cis,trans,cis-configuration (idealized symmetry C2h) as shown in the Scheme, this has never been established unambiguously. Furthermore, (I) fits well into our investigations of bromine–bromine interactions in polybrominated hydrocarbons (Jones et al., 2012, and references therein). We report here the structure of (I) in the solid state, confirming its expected configuration.

The molecule of (I) is shown in Fig. 1; it displays crystallographic inversion symmetry, and the cyclobutane ring is thus exactly planar. The ring C—C bond lengths [1.550 (5) and 1.572 (5) Å; Table 1] are roughly similar to the values discussed by Allen (1984) in a review of cyclobutane and cyclobutene structures, with specific values of 1.552 (4) and 1.559 (3) Å for bonds with trans and cis substituents, respectively (the latter lengthened by eclipsing interactions) when both C atoms bear one non-H substituent; cf. the overall mean bond length of 1.558 (2) Å for all planar cyclobutanes. Bonds as long as 1.57 Å are indeed known for cyclobutanes but tend to be formed only when the relevant C atoms are both doubly substituted. Bond angles in the ring (Table 1) are necessarily close to 90°. The torsion angles C2—C1—C3—Br1 = 179.0 (3) and C1i—C2—C4—Br2 = 166.6 (3)° [symmetry code: (i) -x+1, -y+1, -z+1] show that the C—Br bonds lie in planes approximately parallel to the ring edges; atom Br1 is displaced by 1.086 (13) Å and atom Br2 by 1.218 (12) Å on opposite sides of the ring plane.

The planar form of the cyclobutane ring is energetically unfavourable, at least in the gas phase (Cruz-Cabeza et al., 2012). A search of the Cambridge Structural Database (Version 1.14; Allen, 2002) gave 404 examples of cyclobutane rings with noncyclically attached substituents; as many as 86 had fold angles <2° and most of these were planar by symmetry. A recent review by Allen and co-workers (Cruz-Cabeza et al., 2012) has analysed in detail the unexpectedly frequent occurrence of the planar form of cyclobutane rings in crystal structures and concluded that the higher intramolecular energy (ca 6 kJ mol-1) is compensated by improved intermolecular interactions. These are in turn promoted when crystallographic and molecular inversion centres coincide, as is the case for (I). A packing analysis of (I) is therefore of especial relevance. The packing index as calculated by PLATON (Spek, 2009) is 70.2%. Three weak C—H···Br interactions (Table 2) can be identified but their angles suggest that at least two of them are borderline contacts. The packing is better described in terms of three Br···Br contacts (Table 3) with lengths 3.62–3.75 Å (there are no other such contacts <4.4 Å). The first two of these correspond well in terms of C—Br···Br angles to the `type II' classification of Pedireddi et al. (1994), with one angle ca 90° and one ca 180°, whereas the third is a `type I' contact (the angles are equal, in this case by symmetry). The former are thought to represent significant soft–soft contacts, whereas the latter are often described as `symmetry-generated' with less favourable energies. Contact Nos. 2 and 3 combine to form layers of molecules parallel to (010) (Fig. 2) and these are linked in the third dimension by contact No. 1 (Fig. 3).

In our previous paper (Jones et al., 2012), we introduced, for rings involving Br···Br contacts, a primitive topological description R(n,m) to describe a ring with m Br atoms and n atoms in total. In retrospect, this description could be made more precise by the addition of a third number p, such that R(n,m,p) describes a ring as above involving p Br···Br contacts. The two rings of Fig. 2 then acquire the descriptors R(12,4,2) and R(14,6,4). Clearly, this principle could be extended to chains, the whole method being analogous to the well-known graph sets of Etter (1990), as used for the description of hydrogen bonding.

Related literature top

For related literature, see: Allen (1984, 2002); Bally et al. (1978); Cruz-Cabeza, Libeschuetz & Allen (2012); Etter (1990); Griffin & Peterson (1962, 1963); Hopf & Trabert (1980); Jones et al. (2012); Pedireddi et al. (1994); Peterson et al. (1968); Spek (2009).

Experimental top

The title compound was prepared from the corresponding tetra-alcohol (Griffin & Peterson, 1962, 1963; Peterson et al., 1968) in 50% yield by treatment with triphenyphosphane/bromine in dichloromethane; its spectroscopic data agree with those reported in the literature (Griffin & Peterson, 1962, 1963; Peterson et al., 1968). Single crystals of (I) suitable for an X-ray structural investigation were obtained from ether–pentane.

Refinement top

H atoms were placed at calculated positions, with methylene C—H = 0.99 Å and methine C—H = 1.00 Å, and refined using a riding model, with Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: DIF4 (Stoe & Cie, 1992); cell refinement: DIF4 (Stoe & Cie, 1992); data reduction: REDU4 (Stoe & Cie, 1992); 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).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. [At least one of the symmetry-related atoms needs to be labelled, and the symop given in the caption]
[Figure 2] Fig. 2. A packing diagram for (I), viewed parallel to the b axis in the region y 0. Br···Br contacts are indicated by dashed bonds and are numbered according to Table 3.
[Figure 3] Fig. 3. A packing diagram for (I), viewed parallel to the c axis. Br···Br contacts are indicated by dashed bonds. Contacts 1, which link the layers of Fig. 2 in the third dimension, run diagonally in this view.
cis,trans,cis-1,2,3,4-Tetrakis(bromomethyl)cyclobutane top
Crystal data top
C8H12Br4F(000) = 400
Mr = 427.82Dx = 2.435 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
a = 7.410 (4) ÅCell parameters from 48 reflections
b = 9.742 (4) Åθ = 10–11.5°
c = 8.640 (3) ŵ = 13.75 mm1
β = 110.70 (3)°T = 143 K
V = 583.5 (4) Å3Prism, colourless
Z = 20.48 × 0.30 × 0.30 mm
Data collection top
Stoe STADI-4
diffractometer
1153 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.051
Graphite monochromatorθmax = 27.5°, θmin = 3.1°
ω and θ scansh = 90
Absorption correction: ψ scan
(XPREP; Siemens, 1990)
k = 1210
Tmin = 0.567, Tmax = 1.000l = 1011
2736 measured reflections3 standard reflections every 60 min
1344 independent reflections intensity decay: none
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.035H-atom parameters constrained
wR(F2) = 0.089 w = 1/[σ2(Fo2) + (0.0439P)2 + 0.5416P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max < 0.001
1344 reflectionsΔρmax = 1.06 e Å3
56 parametersΔρmin = 0.85 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0219 (17)
Crystal data top
C8H12Br4V = 583.5 (4) Å3
Mr = 427.82Z = 2
Monoclinic, P21/nMo Kα radiation
a = 7.410 (4) ŵ = 13.75 mm1
b = 9.742 (4) ÅT = 143 K
c = 8.640 (3) Å0.48 × 0.30 × 0.30 mm
β = 110.70 (3)°
Data collection top
Stoe STADI-4
diffractometer
1153 reflections with I > 2σ(I)
Absorption correction: ψ scan
(XPREP; Siemens, 1990)
Rint = 0.051
Tmin = 0.567, Tmax = 1.0003 standard reflections every 60 min
2736 measured reflections intensity decay: none
1344 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0350 restraints
wR(F2) = 0.089H-atom parameters constrained
S = 1.08Δρmax = 1.06 e Å3
1344 reflectionsΔρmin = 0.85 e Å3
56 parameters
Special details top

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.

Br···Br contacts:

3.6242 (0.0016) Br1 - Br2_$2 3.6457 (0.0014) Br1 - Br2_$3 3.7484 (0.0016) Br1 - Br1_$4

108.29 (0.12) C3 - Br1 - Br2_$2 171.81 (0.14) Br1 - Br2_$2 - C4_$2 170.25 (0.12) C3 - Br1 - Br2_$3 79.08 (0.13) Br1 - Br2_$3 - C4_$3 74.43 (0.12) C3 - Br1 - Br1_$4 74.43 (0.12) Br1 - Br1_$4 - C3_$4

===============================

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

- 2.6254 (0.0239) x + 7.8068 (0.0211) y - 2.8133 (0.0294) z = 1.1840 (0.0235)

* 0.0000 (0.0000) C1 * 0.0000 (0.0000) C2 * 0.0000 (0.0000) C1_$1 * 0.0000 (0.0000) C2_$1 1.1447 (0.0084) C3 - 1.1883 (0.0085) C4 1.0859 (0.0132) Br1 - 1.2181 (0.0121) Br2

Rms deviation of fitted atoms = 0.0000

===============================

Operators for generating equivalent atoms: $1 - x + 1, -y + 1, -z + 1 $2 x + 1/2, -y + 1/2, z - 1/2 $3 x, y, z - 1 $4 - x, -y + 1, -z $5 x + 1/2, -y + 1/2, z + 1/2

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Br10.21708 (6)0.38542 (5)0.06009 (5)0.02412 (18)
Br20.17559 (8)0.28606 (5)0.64208 (6)0.0355 (2)
C10.3969 (6)0.4324 (4)0.4086 (5)0.0171 (8)
H10.41390.33060.41930.021*
C20.4072 (5)0.4961 (4)0.5759 (5)0.0167 (8)
H20.30240.56530.56010.020*
C30.2165 (6)0.4675 (4)0.2675 (5)0.0196 (8)
H3A0.20530.56850.25510.024*
H3B0.10320.43370.29170.024*
C40.4147 (7)0.3947 (5)0.7099 (5)0.0261 (10)
H4A0.43030.44430.81380.031*
H4B0.52690.33290.73050.031*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br10.0237 (3)0.0319 (3)0.0147 (2)0.00143 (17)0.00425 (18)0.00532 (15)
Br20.0423 (3)0.0415 (3)0.0261 (3)0.0217 (2)0.0163 (2)0.0064 (2)
C10.0174 (19)0.0182 (17)0.0141 (17)0.0009 (16)0.0036 (15)0.0003 (16)
C20.0132 (18)0.0215 (19)0.0152 (17)0.0003 (15)0.0050 (14)0.0005 (16)
C30.020 (2)0.024 (2)0.0130 (17)0.0018 (16)0.0044 (16)0.0027 (15)
C40.032 (2)0.032 (2)0.0154 (19)0.0133 (19)0.0097 (18)0.0020 (17)
Geometric parameters (Å, º) top
Br1—C31.964 (4)C1—H11.0000
Br2—C41.967 (5)C2—H21.0000
C1—C31.496 (5)C3—H3A0.9900
C1—C21.550 (5)C3—H3B0.9900
C1—C2i1.572 (5)C4—H4A0.9900
C2—C41.508 (6)C4—H4B0.9900
C3—C1—C2113.8 (3)C1—C2—H2111.2
C3—C1—C2i120.0 (3)C1—C3—H3A109.4
C2—C1—C2i90.2 (3)Br1—C3—H3A109.4
C4—C2—C1115.4 (3)C1—C3—H3B109.4
C4—C2—C1i116.3 (3)Br1—C3—H3B109.4
C1—C2—C1i89.8 (3)H3A—C3—H3B108.0
C1—C3—Br1111.1 (3)C2—C4—H4A109.7
C2—C4—Br2109.8 (3)Br2—C4—H4A109.7
C3—C1—H1110.4C2—C4—H4B109.7
C2—C1—H1110.4Br2—C4—H4B109.7
C4—C2—H2111.2H4A—C4—H4B108.2
C3—C1—C2—C4117.5 (4)C2i—C1—C3—Br174.0 (4)
C2i—C1—C2—C4119.2 (4)C1—C2—C4—Br263.3 (4)
C3—C1—C2—C1i123.3 (4)C1i—C2—C4—Br2166.6 (3)
C2—C1—C3—Br1179.0 (3)
Symmetry code: (i) x+1, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1···Br1ii1.003.003.838 (4)142
C4—H4A···Br1iii0.993.123.800 (5)127
C4—H4A···Br1i0.992.963.486 (5)114
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1/2, y+1/2, z+1/2; (iii) x, y, z+1.

Experimental details

Crystal data
Chemical formulaC8H12Br4
Mr427.82
Crystal system, space groupMonoclinic, P21/n
Temperature (K)143
a, b, c (Å)7.410 (4), 9.742 (4), 8.640 (3)
β (°) 110.70 (3)
V3)583.5 (4)
Z2
Radiation typeMo Kα
µ (mm1)13.75
Crystal size (mm)0.48 × 0.30 × 0.30
Data collection
DiffractometerStoe STADI-4
diffractometer
Absorption correctionψ scan
(XPREP; Siemens, 1990)
Tmin, Tmax0.567, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
2736, 1344, 1153
Rint0.051
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.089, 1.08
No. of reflections1344
No. of parameters56
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)1.06, 0.85

Computer programs: DIF4 (Stoe & Cie, 1992), REDU4 (Stoe & Cie, 1992), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XP (Siemens, 1994).

Selected geometric parameters (Å, º) top
C1—C21.550 (5)C1—C2i1.572 (5)
C2—C1—C2i90.2 (3)C1—C2—C1i89.8 (3)
Symmetry code: (i) x+1, y+1, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C1—H1···Br1ii1.003.003.838 (4)141.6
C4—H4A···Br1iii0.993.123.800 (5)127.2
C4—H4A···Br1i0.992.963.486 (5)114.4
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1/2, y+1/2, z+1/2; (iii) x, y, z+1.
Bromine–bromine interactions (Å, °) in (I) top
Interaction No.C—Br···Br'—C'Br···Br'C—Br···Br'Br···Br'—C'
1C3—Br1···Br2iv—C4iv3.624 (2)108.3 (2)171.8 (2)
2C3—Br1···Br2v—C4v3.646 (2)170.3 (2)79.1 (2)
3C3—Br1···Br1vi—C3vi3.748 (2)74.43 (12)74.43 (12)
Symmetry codes: (iv) x+1/2, -y+1/2, z-1/2; (v) x, y, z-1; (vi) -x,-y+1, -z.
 

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