1,4-Bis(hexyloxy)-2,5-diiodobenzene

The centrosymmetric title compound, C18H28I2O2, crystallized in the monoclinic space group P21/c with the alkyl chains having extended all-trans conformations, similar to those in the centrosymmetric bromo analogue [Li et al. (2008 ▶). Acta Cryst. E64, o1930] that crystallized in the triclinic space group P . The difference between the two structures lies in the orientation of the two alkyl chains with respect to the C(aromatic)—O bond. In the title compound, the O—Calkyl—Calkyl—Calkyl torsion angle is 55.8 (5)°, while in the bromo analogue this angle is −179.1 (2)°. In the title compound, the C-atoms of the alkyl chain are almost coplanar [maximum deviation of 0.052 (5) Å] and this mean plane is inclined to the benzene ring by 50.3 (3)°. In the bromo-analogue, these two mean planes are almost coplanar, making a dihedral angle of 4.1 (2)°. Another difference between the crystal structures of the two compounds is that in the title compound there are no halide⋯halide interactions. Instead, symmetry-related molecules are linked via C—H⋯π contacts, forming a two-dimensional network.

Cg1 is the centroid of the C1-C3/C1 i -C3 i ring. The title compound has been used as a building block for the elaboration of organic-electronic materials, for example as a monomer for the synthesis of conjugated polymers (Van Heyningen et al., 2003;Mayor & Didschies, 2003). Our interest in this compound lies in the possibility of using it as a spacer-unit in linked materials for the creation of structured, discotic mesophases. The synthesis of the title compound has been reported by various groups (Van Heyningen et al., 2003;Mayor & Didschies, 2003;Plater et al., 2004). Here it was synthesized by iodination of 1,4-bis(hexyloxy)benzene (Castanet et al., 2002). The crystal structure of the bromo-analogue, synthesized by (Maruyama & Kawanishi, 2002), has been described by (Li et al., 2008).
The molecular structure of the title compound is illustrated in Fig. 1. Bond lengths are normal (Allen et al., 1987) and similar to those in the bromo-analogue (Li et al., 2008).  (Table 1 and Fig. 3; Cg is the centroid of the C1-C3/C1 i -C3 i benzene ring).

Experimental
The title compound was synthesized by iodination of 1,4-bis(hexyloxy)benzene (Castanet et al., 2002). To a solution of 1,4-bis(hexyloxy)benzene (0.75 mmol) and N-iodosuccinimide (2.40 mmol) in dry acetonitrile (5.0 ml) was added trifluoroacetic acid (1.50 mmol) at RT. The mixture was heated and stirred at 363 K for 2 h. The reaction mixture was then cooled to RT and concentrated. Diethyl ether (30 ml) was added and the heterogeneous mixture was filtered to remove the white precipitate of succinimide that had formed. The organic layer was then washed with 10% NaHSO 3 (aq) (3 × 30 ml) and

Refinement
The H-atoms could all be located in difference electron-density maps. In the final cycles of refinement they were included in calculated positions and treated as riding atoms: C-H = 0.98 -0.99 Å, with U iso (H) = k × U eq (parent C-atom), where k = 1.2 for H-aromatic and H-methylene, and 1.5 for H-methyl. Fig. 1. A view of the molecular structure of the title compound, with displacement ellipoids drawn at the 50% probabilty level. Atoms labelled i are related to the other atoms by the symmetry operation -x+1, -y+1, -z.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )
x y z U iso */U eq I1 0.82998 (