Co(III), Co(II), Co(I): Tuning Single Cobalt Metal Atom Oxidation States in a 2D Coordination Network

It is shown that the self-assembly of a surface-confined metal-organic network such as cobalt porphyrins on graphene is accompanied by the evolution of coordination-dependent observables in the electronic structure: variation of the layer's valence states within almost 1 eV range and of the metal atoms oxidation states. Coordination of cobalt porphyrins, driven by Co ad-atoms, allows the synthesis of single metal atom centers with +3, +2, or +1 oxidation states. The electronic structure is determined by lateral interactions extending up to a few nanometers, beyond nearest-neighbor distances. The reactivity of the single Co sites, which is strongly dependent on the local electronic configuration and, thus, on the metal-specific oxidation state, is probed by carbon monoxide, which is found to ligate at pyridinic Co(I) at room temperature for background pressures above a fraction of a mbar. Progressive coordination of single cobalt atoms in a graphene-supported porphyrin-based surface-confined network allows spanning from +1 to +2 and +3 oxidation states. Specific sites become then active toward ligation. image