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 center dot center dot center dot I halogen-bonding interactions, thus giving rise to polymeric chains. The N center dot center dot center dot I interaction observed in 2 (d(N center dot center dot center dot I) = 2.717 angstrom, not less than C(sp)-I center dot center dot center dot N = 175.8 degrees) is quite strong relative to previously reported data. The N center dot center dot center dot I interaction in 5 (d(N center dot center dot center dot 1) = 2.901 angstrom not less than C(sp(2))-I center dot center dot center dot N = 173.6 degrees) 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 center dot center dot center dot 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 center dot center dot center dot O interactions between nearby morpholinium cations, and the second network is based on N-H center dot center dot center dot N hydrogen bonding between morpholimum 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 center dot center dot center dot I) = 3.470 angstrom, not less than C(sp(2))-I center dot center dot center dot I = 170.7 degrees). X-ray crystal studies of 6 show a completely different arrangement from that observed in 4, namely, N-H center dot center dot center dot O interactions are not present. In crystalline 6, morpholinium cations are interconnected through C-H center dot center dot center dot O bridges (d(H center dot center dot center dot O) = 2.521 and 2.676 angstrom), and the NH2+ groups interact with nearby iodide (d(H center dot center dot center dot I) = 2.633 and 2.698 angstrom).