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

Abstract

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 A, angle-spherical C(sp)-I...N=175.8 degrees) is quite strong relative to previously reported data. The N...I interaction in 5 (d(N...I)=2.901 A, angle-spherical C(sp2)-I...N=173.6 degrees) is weaker, in accordance with the order C(sp)-X<--base>C(sp2)-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 A, angle-spherical C(sp2)-I...I=170.7 degrees). 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 A), and the NH2+ groups interact with nearby iodide anions (d(H...I)=2.633 and 2.698 A).

Quantifying the Effects of Halogen Bonding by Haloaromatic Donors on the Acceptor Pyrimidine

“…Studies employing solution-phase NMR demonstrate that not only can the presence of ah alogen bond be determined butt he relative strength of the intermoleculari nteraction of varioush alogen bond donors and their corresponding acceptors can also be elucidated. [26,[54][55][56][57][58][59] For example, the measure of efficiency for ah alogen bond donor (Cl < Br < I) was originally established by using 19 FNMR spectroscopy. [60][61] Fluorinated halogen bond acceptors result in definitively stronger interactions via an inductive effect and result in large high-field shifts in chemical signals upon halogen bonding formation.…”

Enhancement of Iodine–Hydride Interaction by Substitution and Cooperative Effects in NCX–NCI–HMY Complexes

“…[13] The iodine atom forms the strongest halogen bond, thus it can be understood that the halogen bonds in crystal materials and biological systems are often involved with iodine atoms. [14][15][16] Halogen bonding shares some common characteristics in structure, physical properties, strength, and nature with the more commonly encountered hydrogen bonding. Halogen bonding shows a higher directionality than hydrogen bonding due to the anisotropic distribution of electron densities around the halogen atoms.…”

Halogen Bonding: A Supramolecular Entry for Assembling Nanoparticles

“…Important supramolecular forces, including hydrogen and halogen bonding, van der Waals interactions, and p-p stacking have been studied in much detail and used for the design of a vast number of synthons capable of forming task-specific structures having a high level of complexity. Remarkably, although XB is considered as a world parallel to hydrogen bonding [15][16][17] and a useful tool to construct supramolecular complexes and networks, [18] no studies to date have reported control of the formation and structure of large nanoparticle-based assemblies with this specific and directional interaction. [5] Recent reports show the increasing significance of XB in liquid crystals, [6,7] solid-state reactivity, [8] nonporous solids, [9] inorganic chemistry, [10] materials science, [11,12] and biology, [13,14] to mention just a few.…”

“…[5] Recent reports show the increasing significance of XB in liquid crystals, [6,7] solid-state reactivity, [8] nonporous solids, [9] inorganic chemistry, [10] materials science, [11,12] and biology, [13,14] to mention just a few. Remarkably, although XB is considered as a world parallel to hydrogen bonding [15][16][17] and a useful tool to construct supramolecular complexes and networks, [18] no studies to date have reported control of the formation and structure of large nanoparticle-based assemblies with this specific and directional interaction. XB interactions are kinetically labile but are considered to be relatively strong.…”