Site-Dependent Coordination Bonding in Self-Assembled Metal-Organic Networks

The combination of organic linkers with metal atoms on top of inorganic subtrates offers promising perspectives for functional electronic and magnetic nanoscale devices. Typically, coordination bonds between electron-rich end groups and transition-metal atoms lead to the self-assembly of metal-organic nanostructures, whose shape and electronic and magnetic properties curcially depend on the type of ligand. Here, we report on the site-selective bonding properties of Co atoms to the dichotomic dicyanoazobenzene molecule with its carbonitrile and diazo N-based moieties as possible ligands. Using low-temperature scanning tunnelling microscopy (STM) and spectroscopy measurements, we resolve the formation of self-assembled metal-organic motifs. Cobalt atoms exhibit a clear spectroscopic fingerprint dependent on the different coordination site, which is further used to map their position, otherwise not clearly visible in the topographic STM images. Density functional theory corroborates the observed bonding patterns and evidences their coordinative nature.