Aside, the strong adsorption and electron density donation/backdonation mechanism on early TMs is directly related to the coordination number of the CO molecule on the surface, as seen in the preferred sites, listed in Tables S4-S6 of Section S3 of the SM. Those TMs with a stronger interaction tend to have a more significant number of surface TM atoms participating in the molecular coordination. Still, the σ-donation, done through the CO C atom, plus the O electron density, featuring more coulombic/steric repulsion than the C one, leads to CO molecule not being perfectly planar, see Fig. , but with a minor tilt, in between 53º and 72º with respect the TM surface plane, see Tables a more elongated bond than perpendicular cases, with an R of 0.719, see Fig. .