Crystal structures of two bis(iodomethyl)benzene derivatives: similarities and differences in the crystal packing

The molecular and crystal structures of two isomeric bis(iodomethyl)benzene derivatives are reported. A comparison is made of the intermolecular contacts stabilizing the packing in the two closely related systems.


Chemical context
The isomeric xylene derivatives reported here, 1,2-bis(iodomethyl)benzene, (I), and 1,3-bis(iodomethyl)benzene (II), are useful synthons for the preparation of a range of organic compounds. (I) is used particularly in the synthesis of polycyclic aromatic systems (see for example: Takahashi et al. 2006;Abreu et al., 2010;Wang et al., 2012). Similarly (II) has been used in polymer formation (Pandya & Gibson, 1991), in the synthesis of metacyclophanes (Ramming & Gleiter, 1997) and to provide aromatic spacers in organic synthesis (Kida et al., 2005). Our interest in such compounds is as components of ionene polymers. The compounds were readily prepared by metathesis from the bis(bromomethyl)benzene derivatives.

Structural commentary
The molecular structures of 1,2-bis(iodomethyl)benzene, (I), and 1,3-bis(iodomethyl)benzene, (II), are shown in Figs. 1 and 2 and are sufficiently similar to be discussed together. Each comprises a benzene ring with two iodomethyl substituents in the 1,2-and 1,3-positions for (I) and (II) respectively. The ISSN 2056-9890 molecule of (I) lies about a twofold axis that bisects the C-C bond between the two iodomethyl substituents. For each molecule the C-I bonds of the substituents point away from opposite faces of the benzene rings with the C-C-I planes almost orthogonal to the ring planes; dihedral angles = 87.99 (14) for (I) and 82.23 (14) and 83.61 (15) for (II). The C1-C11 and C11-I1 bond lengths in (I) and C1-C11, C11-I1, C3-C31 and C31-I3 in (II) are reasonably self-consistent and also compare well with those found in the isomeric 1,4bis(iodomethyl)benzene (McAdam et al. 2009).

Figure 3
stacking interactions (green dotted lines) supported by C-HÁ Á ÁI hydrogen bonds for (I). Hydrogen bonds in this and subsequent figures are drawn as blue dashed lines.

Figure 4
Chains of molecules of (I) in [101].
bonds and generate a three dimensional network structure, Fig. 5.

Crystal packing for (II)
In the crystal of (II), C11-H11BÁ Á ÁI1 hydrogen bonds, Table 2, form a column supported by a series of C31-H31BÁ Á ÁCg1 contacts. C31-H31AÁ Á ÁI3 hydrogen bonds link these in an obverse fashion, forming double chains along b, Overall packing for (I) viewed along the c-axis direction. Table 2 Hydrogen-bond geometry (Å , ) for (II).

Figure 6
Double chains of molecules of (II) formed by a series of C31-H31BÁ Á ÁCg1 contacts (green dotted lines) linked by C-HÁ Á ÁI hydrogen bonds.

Figure 7
Sheets of molecules of (II) in the ab plane formed by C-HÁ Á ÁI. hydrogen bonds.

Synthesis and crystallization
Preparation of the title compounds was based on literature methods (Moore & Stupp, 1986;Kida et al., 2005). The appropriate bis(bromomethyl)benzene (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, the crystals that developed were rinsed gently with water to remove sodium bromide and air dried. The product was recrystallized a second time from acetone to give X-ray quality crystals. Confirmation of the metathesised (iodo) product was by microanalysis and mass spectroscopy. 13

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. One low angle reflection with F o << Fc was omitted from the final refinement cycles.