Topological Analysis of Hydroxyquinoline Derivatives Interacting with Aluminum Cations or with an Al(111) Surface

The reactivity of hydroxyquinoline derivatives (native molecules (Hq) and modified species (HqX, X = Br, SO₃H, or SO₃^-)) is investigated either (i) with aluminum cations for the formation of chelates or (ii) with aluminum surfaces for their adsorption properties, in the framework of the dispersion-corrected Density Functional Theory (DFT-D). It is shown that the substituent X has no influence on the complexation to the aluminum cation of the deprotonated active form, i.e., the one exhibiting a phenolate moiety and referred to as q^- for the native Hq and qX (n = 1 or 2) for its derivatives. The formation energies of the Alq and Al(qX) complexes, taking values of -60.87 ± 3.10 eV in vacuum and -24.30 ± 0.29 eV in water, are indicative of a strong chelating affinity of the q^- and qX (n = 1 or 2) anions for the aluminum cations. ELF and QTAIM topological analyses on these complexes evidence that the bonding of the deprotonated species with the Al³⁺ ion is ionic with a very weak covalence degree. The para or ortho substituent X of the phenolate moiety of the qX (n = 1 or 2) derivatives modifies the electronic structure only locally and thus does not influence their O- or N-coordinating properties. The adsorption properties of the latter on an Al(111) surface have also been studied within periodic DFT-D calculations. The adsorbed species are strongly interacting with the Al(111) surface, as shown by the value of the adsorption energy of -3.69 ± 0.21 eV for the most stable geometries. Various adsorption modes of the q^- and qX (n = 1 or 2) derivatives are characterized on the Al surface, depending on stabilizing or destabilizing interactions with the substituents X. On the basis of QTAIM descriptors, the bonding of the hydroxyquinoline species on the aluminum surface is characterized as ionic with a weak covalent character.