Structure and bonding between an aryl group and metal surfaces

Modifying solid surfaces with aryl groups has many potential applications. Using first principles density functional theory methods, we investigated the trend of the structure and bonding of the phenyl group (C₆H₅, the simplest aryl group) on selected transition metals across the periodic table. We found that the bond between C₆H₅ and metal surfaces is chemical in nature. Decreasing bond strength is found from left to right, concurrent with a switching of the preferred orientation for C₆H₅ from the flat-lying configuration to the upright configuration. This switching is attributed to the increasing of d-electrons; that is, early transition metals, lacking d-electrons, favor the carbon-metal π-bond and therefore the flat-lying configuration, while late transition metals rich in d-electrons prefer the carbon-metal σ-bond and thus the upright fashion. C₆H₅ is also found to undergo β-dehydrogenation on early transition metals. This work invites further theoretical and experimental research on the aryl-solid interface.