Low-Dimensional Metal–Organic Coordination Structures on Graphene

We report the formation of one- and two-dimensional metal–organic coordination structures from para-hexaphenyl-dicarbonitrile (NC–Ph6–CN) molecules and Cu atoms on graphene epitaxially grown on Ir(111). By varying the stoichiometry between the NC–Ph6–CN molecules and Cu atoms, the dimensionality of the metal–organic coordination structures could be tuned: for a 3:2 ratio, a two-dimensional hexagonal porous network based on threefold Cu coordination was observed, while for a 1:1 ratio, one-dimensional chains based on twofold Cu coordination were formed. The formation of metal–ligand bonds was supported by imaging the Cu atoms within the metal–organic coordination structures with scanning tunneling microscopy. Scanning tunneling spectroscopy measurements demonstrated that the electronic properties of NC–Ph6–CN molecules and Cu atoms were different between the two-dimensional porous network and one-dimensional molecular chains