X⋅⋅⋅X Halogen Bond‐Induced Supramolecular Helices

Abstract

The halogen bond is the attractive interaction between the electrophilic region of ah alogen atom and the nucleophilic region of another molecular entity,e merging as afavorable manner to manipulate supramolecular chirality in self-assemblies.Engineering halogen bonded helical structures remains achallenge due to its sensitivity to solvent polarity and competitive forces like hydrogen bonds.H erein, we report aX•••X (X = Cl, Br,I)type weak halogen bond that induces the formation and evolution of supramolecular helical structures both in solid and solution state.T he p-conjugated phenylalanine derivatives with F, Cl, Br and Is ubstitution selfassembled into 2 1 helical packing driven by hydrogen bond and halogen bond, respectively.The specific molecular geometries of p-conjugated amino acids gave rise to multiple noncovalent forces to stabilizet he X•••X halogen bond with small bond energies ranging from À0.69 to À1.49 kcal mol À1 .H alogen bond induced an opposite helicity compared to the fluorinated species,a ccompanied by the inversed circularly polarized luminescence.

Enhancement of Halogen Bond Strength by Intramolecular H-Bonds

“…These and many other attributes of the HB have been thoroughly elucidated over more than a century, and are laid out in countless papers and monographs. − The study of the parallel XB is advancing quickly, leading to the establishment of a number of general rules and principles that guide our understanding of this phenomenon. − It is commonly understood, for example, that this bond strengthens as the X atom grows larger, commonly attributed to an associated rise in its electropositivity and polarizability. The highly compact and electronegative F atom very rarely participates in a XB, and then only under certain limited conditions .…”

Halogen bonding–driven chiral amplification of a bimetallic gold-copper cluster through hierarchical assembly

“…These characteristics make it highly favorable for driving the fabrication of chiral assemblies. Diverse halogen bonding interactions, C─I• + , and X•••X, provide an additional powerful tool for designing and controlling the chirality of supramolecular structures (21)(22)(23)(24)(25), expanding the possibilities for creating functional materials with tailored properties. However, the directed hierarchical assemblies, particularly chiral ones, driven by halogen bonding, still present notable challenges and unexplored opportunities.…”

Properties and Stabilities of Cyclic and Open Chains of Halogen Bonds

“…The variety of noncovalent bond which has garnered the earliest and most widespread attention to date, has been the halogen bond (XB). − In its simplest manifestation, the R substituent in an RX molecule draws electron density toward itself along the R–X σ-bond, leaving a deficit along this axis. This density depletion, and the accompanying positive electrostatic potential, is commonly referred to as a σ-hole, which contrasts with the negative potential around the equator of the R–X axis, in the vicinity of the X lone pairs.…”