Visualizing halogen bonds in planar supramolecular systems

Supramolecular interactions were studied in two planar model systems, 1,5- and 2,6-dibromoanthraquinones, prepared on Au(111) using scanning tunneling microscopy. In both systems, we found rigid triangular structures that consisted of simultaneous halogen bonds and hydrogen bonds, as reported in protein-ligand complexes. We proposed molecular models that were well reproduced by first-principle studies and could be explained by halogen and hydrogen bonds. The distances, angles, and, strengths of the intermolecular bonds were measured in the observed structures, and showed good agreement with existing bulk data.