Tetragonal porous networks made by rod-like molecules on Au(1 1 1) with halogen bonds

Supramolecular structures of two rod-like molecules whose both ends are terminated with Br-ligands were studied using scanning tunneling microscopy (STM). Rectangular and square porous networks were observed in 4,4″-dibromo-p-terphenyl (DBTP) and 4,4″-dibromo-p-quaterphenyl (DBQP) molecules on Au(1 1 1) with the void areas of 3.5 and 5.6 nm², respectively. Both networks had chiral quadrupole nodes that could be explained with four Br⋯Br halogen bonds and four Br⋯H hydrogen bonds. The reversible transformations of network structures were observed in consecutive STM images, possibly mediated by a liquid phase surrounding the networks. The molecules also formed close-packing ladder-like networks with triple nodes that could be explained with four Br⋯H bonds. Our study shows that Br-ligands play key roles in forming molecular networks for both rod-like molecules.