The interaction between benzene and the Cu(111) surface can be explained by the Dewar, Chatt, Duncanson model in which electron density is donated from the adsorbate HOMO to the metal surface, with concomitant back donation from the surface to the molecular LUMO. During surface adsorption the C-C bonds elongate since an MO which is pi-bonding between adjacent carbon atoms is depopulated, and an MO which is C-C pi-antibonding becomes partially filled. We, on the other hand, report a first-principles study which illustrates that back donation from a coinage metal surface into the LUMO of an organic adsorbate can actually strengthen the intramolecular bond within the organic. This finding is in stark contrast to the countless examples which illustrate that back donation results in a weakening and lengthening of the bond into which electron density is donated. We further illustrate that the level alignment between the Fermi level of the surface and the frontier molecular orbitals of the organic, the topology of the LUMO and its overlap with the metal bands are important in discovering molecule/surface combinations which may result in bond strengthening as a result of backdonation. Finally, the effect of the coverage on the change in the bond lengths is examined.

Surface induced bond strengthening via back donation: A first-principles discovery

247th National Meeting (2014)

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