Halogen and Hydrogen Bond Architectures in Switchable Chains of Di- and Trihaloimidazoles

Halogen bonds have been employed for controlling the structure of (NHN)-N-... hydrogen-bonded chains in halogenated imidazoles; the CH(...)halogen contacts stabilize the coplanar arrangement of molecules, whereas the halogen(...)halogen contacts twist the molecules around the NH...N bonds and stretch their (NN)-N-... distances. The interplay of halogen...halogen and NH...N hydrogen bonds leads to isostructural relations of 4,5-dihaloimidazoles as well as between trichloro- and tribromoimidazole. However, the increasing steric hindrance excludes the triiodoimidazole from this isostructural series, and the triiodo derivative forms an unusual structure with three symmetry-independent molecules. All symmetrically substituted 4,5-dichloro-, dibromo-, and diiodoimidazoles as well as trichloro-, tribromo-, and triiodoimidazoles have been synthesized and crystallized and their structures determined. The derived rules also apply to the co-crystal structures of 4,5-diiodoimidazole:2,4,5-triiodoimidazole as well as to 4-iodoimidazole:2,4-diiodoimidazole. The halogen interactions prove an efficient means for engineering and tuning new materials with desired dielectric properties relying on highly polarizable (NHN)-N-... hydrogen bonds.