1,4-Bis(iodo­meth­yl)benzene

The centrosymmetric title compound, C₈H₈I₂, was prepared by metathesis from the dibromo analogue. In the crystal structure, weak C—H⋯I inter­actions link the mol­ecules into stacks down the b axis. The structure is further stabilized by short I⋯I contacts [3.8433 (2) Å], forming undulating sheets in the (101) plane.

Related literature

For the synthesis, see: Moore & Stupp (1986); Kida et al. (2005). For related structures, see: Basaran et al. (1992); Fun et al. (2009); Jones & Kus (2007); Zhang et al. (2007). For applications of dihalo-p-xylenes in living radical polymerization processes, see: Samakande et al., (2007); Asandei et al. (2008). For other polymer applications, see: Leir & Stark (1989); Hochberg & Schulz (1993). For additional applications of dihalo-p-xylenes, see: Le Baccon et al. (2001); Sobransingh & Kaifer (2006); Song et al. (2008); Au et al. (2009). For details of halogen⋯halogen inter­actions, see: Pedireddi et al. (1994) and for reference structural data, see: Allen et al. (1987).

Experimental

Crystal data

• C₈H₈I₂

• M_r = 357.94

• Monoclinic, P 2₁ /c

• a = 9.0978 (3) Å

• b = 4.5982 (2) Å

• c = 11.2793 (3) Å

• β = 99.808 (1)°

• V = 464.96 (3) ų

• Z = 2

• Mo Kα radiation

• μ = 6.69 mm⁻¹

• T = 89 K

• 0.21 × 0.15 × 0.03 mm

Data collection

• Bruker APEXII CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2006) T_min = 0.410, T_max = 0.818

• 8198 measured reflections

• 1674 independent reflections

• 1538 reflections with I > 2σ(I)

• R_int = 0.026

Refinement

• R[F² > 2σ(F²)] = 0.013

• wR(F²) = 0.033

• S = 1.06

• 1674 reflections

• 62 parameters

• All H-atom parameters refined

• Δρ_max = 0.51 e Å⁻³

• Δρ_min = −0.51 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C4—H42⋯I1^i	1.02 (2)	3.12 (2)	3.9774 (16)	141.8 (16)
Symmetry code: (i) x, y+1, z.

Data collection: APEX2 (Bruker 2006); cell refinement: APEX2 and SAINT (Bruker 2006); data reduction: SAINT; program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) and TITAN (Hunter & Simpson, 1999); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97, enCIFer (Allen et al., 2004), PLATON (Spek, 2009) and publCIF (Westrip, 2009).

Supporting information

S1. Comment

Dihalo-p-xylenes are extensively used in polymer science (Leir & Stark, 1989; Hochberg & Schulz, 1993; Samakande et al., 2007) and as a versatile synthon for –CH₂—C₆H₄—CH₂– connective units in other areas of chemistry (Le Baccon et al., 2001; Song et al., 2008; Au et al., 2009). The bulk of this work utilizes the commercially available α,α'-dibromo-p-xylene, but the diiodo- derivative offers additional reactivity (Moore & Stupp, 1986; Sobransingh & Kaifer, 2006; Asandei et al., 2008). Our interest in the title compound, (I), Fig. 1, is as one of the components in xylene bridged electroactive gels. In these, the chemical links are quaternary amines formed by reaction of the alkylhalogen termini with amine residues in the other gel component.

The molecule lies about an inversion centre located at the centroid of the benzene ring. The C1···C4 atoms lie in a plane (r.m.s. deviation 0.01 Å) and the C—C and C—I distances in the molecule are unremarkable (Allen et al., 1987). This structure is the fourth in a series of XCH₂C₆H₄CH₂X molecules; X = F, II (Fun et al., 2009); Cl, III (Basaran et al., (1992); Br, IV (Jones & Kus, 2007; Zhang et al., 2007). All four molecules are closely isostructural with only the C—halogen bond distance distinguishing them. Indeed the CH₂C₆H₄CH₂ fragment of the title compound overlays with corresponding portions of the related molecules with r.m.s. deviations, 0.032 Å for II, 0.013 Å for III and 0.007 Å for IV respectively (Macrae et al., 2006).

In the crystal structure, weak C—H···I interactions and short I···I contacts, 3.8433 (2) Å, form undulating sheets in the 101 plane, Fig. 2. Each I atom interacts with two adjacent iodine atoms (symmetry operations 2 - x, -1/2 + y, 1/2 - z and 2 - x, 1/2 + y, 1/2 - z). The I···I contacts observed here fit with the type II designation of halogen···halogen interactions proposed previously (Pedireddi et al. 1994). The packing arrangement for I is closely similar to that observed for IV, (Jones & Kus, 2007; Zhang et al., 2007). I, III and IV all crystallize in the space group P21/c with unit cells that differ only in a small but significant increase in volume as the size of the halogen increases.

Related literature

For the synthesis, see: Moore & Stupp (1986); Kida et al. (2005). For related structures, see: Basaran et al. (1992); Fun et al. (2009); Jones & Kus (2007); Zhang et al. (2007). For applications of dihalo-p-xylenes in living radical polymerization processes, see: Samakande et al., (2007); Asandei et al. (2008). For other polymer applications, see: Leir & Stark (1989); Hochberg & Schulz (1993). For additional applications of dihalo-p-xylenes, see: Le Baccon et al. (2001); Sobransingh & Kaifer (2006); Song et al. (2008); Au et al. (2009). For details of halogen···halogen interactions, see: Pedireddi et al. (1994) and for reference structural data, see: Allen et al. (1987).

S2. Experimental

The title compound was prepared by a combination of the methods of Moore & Stupp (1986) and Kida et al. (2005). Thus α,α'-dibromo-p-xylene (1.32 g, 5 mmol) was refluxed for 7 h with sodium iodide (2.25 g, 15 mmol) in acetone (25 ml). The solution was allowed to cool overnight, and the resulting yellow plates of (I) that developed were rinsed gently with water to remove sodium bromide and air dried. Confirmation of the metathesized (iodo) product was by microanalysis, mass spectroscopy and diagnostic tests. ¹H and ¹³C NMR spectra are distinct from those of the dibromo precursor.

S3. Refinement

All H-atoms were located in a difference Fourier map and refined freely.

Computing details

Data collection: APEX2 (Bruker 2006); cell refinement: APEX2 (Bruker 2006) and SAINT (Bruker 2006); data reduction: SAINT (Bruker 2006); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) and TITAN (Hunter & Simpson, 1999); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008), enCIFer (Allen et al., 2004), PLATON (Spek, 2009) and publCIF (Westrip, 2009).

Figures

	Fig. 1. The structure of (I) with displacement ellipsoids for the non-hydrogen atoms drawn at the 50% probability level. Unlabelled atoms are generated by the symmetry operation (1–x, –y, 1–z).
	Fig. 2. Crystal packing for (I) viewed down the b axis with hydrogen bonds and short I···I contacts drawn as dashed lines.

1,4-bis(iodomethyl)benzene

Crystal data

C8H8I2	F(000) = 324
Mr = 357.94	Dx = 2.557 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 5590 reflections
a = 9.0978 (3) Å	θ = 2.3–33.0°
b = 4.5982 (2) Å	µ = 6.69 mm^−1
c = 11.2793 (3) Å	T = 89 K
β = 99.808 (1)°	Rectangular plate, pale yellow
V = 464.96 (3) Å^3	0.21 × 0.15 × 0.03 mm
Z = 2

Data collection

Bruker APEXII CCD area-detector diffractometer	1674 independent reflections
Radiation source: fine-focus sealed tube	1538 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
ω scans	θmax = 33.4°, θmin = 3.7°
Absorption correction: multi-scan (SADABS; Bruker, 2006)	h = −13→13
Tmin = 0.410, Tmax = 0.818	k = −5→7
8198 measured reflections	l = −16→16

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)] = 0.013	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.033	All H-atom parameters refined
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0145P)^2 + 0.1407P] where P = (Fo^2 + 2Fc^2)/3
1674 reflections	(Δ/σ)max = 0.001
62 parameters	Δρmax = 0.51 e Å^−3
0 restraints	Δρmin = −0.51 e Å^−3

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.

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.62504 (16)	0.1521 (3)	0.47504 (13)	0.0138 (2)
C2	0.63784 (17)	−0.0405 (3)	0.57245 (14)	0.0154 (3)
C3	0.51429 (17)	−0.1903 (3)	0.59710 (14)	0.0154 (3)
C4	0.75717 (18)	0.3189 (4)	0.45106 (15)	0.0190 (3)
I1	0.880515 (9)	0.07951 (2)	0.331669 (8)	0.01438 (4)
H2	0.729 (3)	−0.073 (4)	0.620 (2)	0.021 (6)*
H41	0.841 (3)	0.354 (5)	0.524 (2)	0.031 (6)*
H3	0.523 (2)	−0.330 (5)	0.6678 (19)	0.022 (5)*
H42	0.733 (3)	0.509 (5)	0.405 (2)	0.021 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0142 (6)	0.0109 (6)	0.0180 (6)	−0.0017 (5)	0.0078 (5)	−0.0032 (5)
C2	0.0133 (6)	0.0159 (7)	0.0174 (7)	0.0007 (5)	0.0038 (5)	−0.0010 (5)
C3	0.0175 (6)	0.0126 (6)	0.0175 (6)	0.0006 (5)	0.0070 (5)	0.0012 (5)
C4	0.0191 (7)	0.0150 (7)	0.0258 (8)	−0.0039 (5)	0.0124 (6)	−0.0051 (6)
I1	0.01367 (5)	0.01628 (6)	0.01473 (5)	−0.00037 (3)	0.00680 (3)	0.00092 (3)

Geometric parameters (Å, º)

C1—C3^i	1.396 (2)	C3—C1^i	1.396 (2)
C1—C2	1.401 (2)	C3—H3	1.01 (2)
C1—C4	1.489 (2)	C4—I1	2.1907 (15)
C2—C3	1.386 (2)	C4—H41	1.04 (2)
C2—H2	0.92 (2)	C4—H42	1.02 (2)
C3^i—C1—C2	118.88 (13)	C1^i—C3—H3	118.7 (12)
C3^i—C1—C4	120.68 (14)	C1—C4—I1	111.52 (10)
C2—C1—C4	120.42 (14)	C1—C4—H41	116.4 (13)
C3—C2—C1	120.64 (14)	I1—C4—H41	100.5 (13)
C3—C2—H2	119.1 (14)	C1—C4—H42	114.9 (13)
C1—C2—H2	120.3 (14)	I1—C4—H42	101.8 (13)
C2—C3—C1^i	120.48 (14)	H41—C4—H42	109.8 (19)
C2—C3—H3	120.9 (12)
C3^i—C1—C2—C3	−0.1 (2)	C3^i—C1—C4—I1	−91.95 (15)
C4—C1—C2—C3	178.24 (14)	C2—C1—C4—I1	89.71 (15)
C1—C2—C3—C1^i	0.1 (2)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H42···I1^ii	1.02 (2)	3.12 (2)	3.9774 (16)	141.8 (16)

Symmetry code: (ii) x, y+1, z.