The Magnetic Behaviour of CoTPP Supported on Coinage Metal Surfaces in the Presence of Small Molecules: A Molecular Cluster Study of the Surface trans -Effect.

Density functional theory, combined with the molecular cluster model, has been used to investigate the surface trans -effect induced by the coordination of small molecules L (L = CO, NH 3 , NO, NO 2 and O 2 ) on the cobalt electronic structure of cobalt tetraphenylporphyrinato (CoTPP) surface-supported on coinage metal surfaces (Cu, Ag, and Au). Regardless of whether L has a closed- or an open-shell electronic structure, its coordination to Co takes out the direct interaction between Co and the substrate eventually present. The CO and NH 3 bonding to CoTPP does not influence the Co local electronic structure, while the NO (NO 2 and O 2 ) coordination induces a Co reduction (oxidation), generating a 3d 8 Co I (3d 6 Co III ) magnetically silent closed-shell species. Theoretical outcomes herein reported demonstrate that simple and computationally inexpensive models can be used not only to rationalize but also to predict the effects of the Co-L bonding on the magnetic behaviour of CoTPP chemisorbed on coinage metals. The same model may be straightforwardly extended to other transition metals or coordinated molecules.