Imaging the halogen bond in self-assembled halogenbenzenes on silver

Visualizing halogen bonding Even though halogen atoms are highly electronegative, a noncovalent bond can form between an electron donor and a halogen atom in a covalent bond. Such interactions are facilitated by the formation of electron-depleted regions in the halogen's covalent bond, a situation least likely for fluorine atoms. Han et al. used noncontact scanning tunneling microscopy with submolecular resolution to explore how the size and polarizability of halogens affect complex formation by halogenated benzene molecules adsorbed on a silver surface (see the Perspective by Neaton). With the help of density functional theory, they show how several weak interactions, including van der Waals forces, electrostatic repulsions, and halogen bonds, affect structure. Science , this issue p. 206 ; see also p. 167