Molecular Assemblies from Imidazolyl‐Containing Haloalkenes and Haloalkynes: Competition between Halogen and Hydrogen Bonding

The structural characterization of molecular assemblies constructed from imidazolyl‐containing haloalkenes and haloalkynes is reported. 1‐(3‐Iodopropargyl)imidazole ( 2 ) and 1‐(2,3,3‐triiodoallyl)imidazole ( 5 ) were synthesized from 1‐propargylimidazole ( 1 ). In the solid state, these wholly organic modules self‐assemble through N⋅⋅⋅I halogen‐bonding interactions, thus giving rise to polymeric chains. The N⋅⋅⋅I interaction observed in 2 ( d (N⋅⋅⋅I)=2.717 Å, ∢C(sp)‐I⋅⋅⋅N=175.8°) is quite strong relative to previously reported data. The N⋅⋅⋅I interaction in 5 ( d (N⋅⋅⋅I)=2.901 Å, ∢C(sp 2 )‐I⋅⋅⋅N=173.6°) is weaker, in accordance with the order C(sp)‐X←base>C(sp 2 )‐X←base. Compound 5 was found to give a 1:1 cocrystal 4 with morpholinium iodide ( 6 ). In the X‐ray crystal studies of 4 , N⋅⋅⋅I halogen‐bonding interactions similar to those observed in 5 were shown not to be present, as the arrangement of the molecules is governed by two interwoven hydrogen‐bonding networks. The first network involves N‐H⋅⋅⋅O interactions between nearby morpholinium cations, and the second network is based on N‐H⋅⋅⋅N hydrogen bonding between morpholinium cations and imidazolyl groups. Both hydrogen‐bonding schemes are charge‐assisted. Halogen bonding is not completely wiped out, however, as the triiodoalkene fragment forms a halogen bond with an iodide anion in its vicinity ( d (I⋅⋅⋅I)=3.470 Å, ∢C(sp 2 )‐I⋅⋅⋅I=170.7°). X‐ray crystal studies of 6 show a completely different arrangement from that observed in 4 , namely, N‐H⋅⋅⋅O interactions are not present. In crystalline 6 , morpholinium cations are interconnected through C‐H⋅⋅⋅O bridges ( d (H⋅⋅⋅O)=2.521 and 2.676 Å), and the NH 2 + groups interact with nearby iodide anions ( d (H⋅⋅⋅I)=2.633 and 2.698 Å).