Halogen Bonds Fabricate 2D Molecular Self-Assembled Nanostructures by Scanning Tunneling Microscopy

Yi Wang,Wenli Deng,Xinrui Miao

doi:10.3390/cryst10111057

Abstract

Halogen bonds are currently new noncovalent interactions due to their moderate strength and high directionality, which are widely investigated in crystal engineering. The study about supramolecular two-dimensional architectures on solid surfaces fabricated by halogen bonding has been performed recently. Scanning tunneling microscopy (STM) has the advantages of realizing in situ, real-time, and atomic-level characterization. Our group has carried out molecular self-assembly induced by halogen bonds at the liquid–solid interface for about ten years. In this review, we mainly describe the concept and history of halogen bonding and the progress in the self-assembly of halogen-based organic molecules at the liquid/graphite interface in our laboratory. Our focus is mainly on (1) the effect of position, number, and type of halogen substituent on the formation of nanostructures; (2) the competition and cooperation of the halogen bond and the hydrogen bond; (3) solution concentration and solvent effects on the molecular assembly; and (4) a deep understanding of the self-assembled mechanism by density functional theory (DFT) calculations.

Highlights

A halogen bond (XB) is a broader class of noncovalent interaction, which was defined by the International Union of Pure and Applied Chemistry (IUPAC) in 2013 [1]
The results indicate that the type-I Br···Br contact is often accompanied by the hydrogen bond (HB) supported by the same Br atom [40]
The results demonstrate that dimers of M1 containing Br···π XB (dimer I) has a high binding energy derived from the collaboration of C−H···Br···π bonds and the rigid directionality of C−Br···π

Summary

The Definition of Halogen Bonds

A halogen bond (XB) is a broader class of noncovalent interaction, which was defined by the International Union of Pure and Applied Chemistry (IUPAC) in 2013 [1]. This definition states that “A halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity.”. A region of lower electron density (σ-hole) gives rise to a cap of deficient electron density on the extension of the R−X covalent bond, which can act as the attractive electron-rich region. The XBs will be explained by the existence of a positive σ-hole on top of the halogen atom

The History Perspective of XB

The Investigation and Application of XB Focus on Crystal Engineering

The General Description of XB in 2D Crystal Engineering

Bifunctional Effect of Benzene Derivative

Conclusions