8-Hydroxyquinoline complexes (Alq(3)) on Al(111): atomic scale structure, energetics and charge distribution

8-Hydroxyquinoline (8Hq) is known to efficiently inhibit the corrosion of aluminium by forming metal-organic layers (8Hqforms complexes with aluminium atoms). In the present work, the atomic scale structure and the energetics of 8-hydroxyquinoline complexes (Alq(3)) adsorbed on an aluminium surface are investigated by dispersion-corrected DFT computations. Two scenarios are considered: (i) anAlq(3)complex, previously formed in vacuum, is deposited on a flat Al(111) surface or (ii) three deprotonated8Hqmolecules (q) directly adsorb on a defective Al(111) surface presenting Al adatoms (Al-Al(111)). For theAlq(3)formation in vacuum, each addition of aqmolecule on the Al atom stabilises the system, the oxidation state of the Al atom evolving from Al(I)inAlqto Al(III)inAlq(2)andAlq(3). The subsequent deposition ofAlq(3)on Al(111) leads to a strong bonding between theqmolecules of the complex and the Al(111) surface, with a significant electron transfer occurring from the surface to the complexes (0.73 to 1.57e). The formation on the metal surface ofAlq(3)complexesviathe adsorption ofqmolecules on an Al adatom leads to more stable structures than the ones obtained from direct adsorption ofAlq(3)on Al(111). For the most stable adsorption conformation, the threeqmolecules are bonded to the Al adatom but only two are bonded to the aluminium surface. In that case, the total electron transfer from the Al-Al(111) surface to theqmolecules is 4.40eand the electron transfer from the Al(111) surface to theAlq(3)-like species is 2.04e. The structure, energetics and charge distribution data demonstrate an iono-covalent bonding between theqmolecules and the Al atoms, in the complex as well as on the aluminium surface.