Abstract
The title crystals, C7H2I3N, are isomorphous. Both mol-ecules lie across two crystallographic mirror planes and a twofold axis. The principal supra-molecular inter-action is centric R22(10) CN/NC⋯I short contacts involving both ortho I atoms, with two contacts bis-ecting each cyano and iso-cyano group. These form ribbons along [010] and give rise to a planar sheet structure parallel to (100). All pairs of adjacent sheets have centric stacking, a mode not previously reported for sheets of this type. This study completes the series of homo-2,4,6-trihalobenzo-nitriles, in which I atoms give the strongest CN⋯X and NC⋯X inter-actions (X = F, Cl, Br, I).
Highlights
Each CN group is bisected by two CNÁ Á ÁH contacts (Fig. 2a; Britton, 2008)
In 2,4,6-tribromobenzonitrile (Br3CN), no CNÁ Á ÁH contacts are found, and each CN group is bisected by two CNÁ Á ÁBr contacts (Fig. 2c; Britton et al, 2016)
The ortho I atoms (I2, I20; I12, I120) are scissored slightly toward the ipso C atom (C1; C11), which is probably caused by the intermolecular CNÁ Á ÁI and NCÁ Á ÁI short contacts
Summary
The strength of cyano–halo interactions tends to increase with increasing polarizability, or the elemental period, of the halogen. Structure-directing CNÁ Á ÁF interactions are usually not observed (Bond et al, 2001). When the halo atom is moved to the 2-position, R22(10) CNÁ Á ÁX rings can form, usually as inversion dimers. Halogenation at both ortho positions allows the formation of CNÁ Á ÁX-derived ribbons or sheets. Each CN group is bisected by two CNÁ Á ÁH contacts (Fig. 2a; Britton, 2008). In 2,4,6-tribromobenzonitrile (Br3CN), no CNÁ Á ÁH contacts are found, and each CN group is bisected by two CNÁ Á ÁBr contacts (Fig. 2c; Britton et al, 2016).
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