Bonding Motifs in Metal–Organic Compounds on Surfaces

The bonds in metal organic networks on surfaces govern the
resulting geometry as well as the electronic properties. Here, we study the
nature of these bonds by forming phenazine−copper complexes on a copper
surface by means of atomic manipulation. The structures are characterized by
a combination of scanning probe microscopy and density functional theory
calculations. We observed an increase of the molecule−substrate distance
upon covalent bond formation and an out-of-plane geometry that is in direct
contradiction with the common expectation that these networks are steered
by coordination bonds. Instead, we find that a complex energy balance of
hybridization with the substrate, inhomogeneous Pauli repulsion, and elastic
deformation drives the phenazine−copper interaction. Most remarkably, this attractive interaction is not driven by electron
acceptor properties of copper but is of completely different donation/back-donation mechanism between molecular π-like
orbitals and sp-like metal states. Our findings show that the nature of bonds between constituents adsorbed on surfaces does not
have to follow the common categories.