Conveying chirality onto the electronic structure of achiral metals:: (R,R)-tartaric acid on nickel

Nickel modified by the chiral molecule (R,R)-tartaric acid yields one of the most successful heterogeneous enantioselective catalysts. We have recently shown that the geometric consequence of adsorbing the doubly deprotonated (R, R)-bitartrate on Ni(110) is to force the bonding Ni atoms to describe a chiral footprint at the surface. Here, we analyse the electronic consequences of chiral molecule-achiral metal adsorption via a detailed analysis of the charge distribution and electronic states of (R, R)-bitartrate adsorbed to four Ni atoms. Gas phase (R, R)-bitartrate was found to carry a chiral asymmetry in the charge distribution at the oxygen atoms of the bonding carboxylate groups, showing there is direct electronic communication of chirality from the molecule's chiral centres to its bonding groups. Upon adsorption to the nickel atoms, this electronic asymmetry is removed and, instead, the chiral signature is transferred into the hybridised molecule-metal electron states which are responsible for the charge transfer between the bonding oxygens and the nickel atoms. Furthermore, chiral inequivalence is observed in the four Ni-O bonds, and, consequently, also in the single-electron wavefunctions centred at the four nickel atoms. As a result, the adsorption site, made up of the four nickel atoms, possesses an electronic structure composed of chiral single-electron wavefunctions. This clearly demonstrates that the induction of chirality from an organic molecule to a metal occurs at the level of single-electron states. We would expect this chirality to be conveyed, via Ni-Ni metallic bonds, onto an extended metal surface. Finally, we also predict chiral responses of the surface electron structure upon excitation e.g. by photons. (C) 2004 Elsevier B.V. All rights reserved.