Coordination of Ethylamine on Small Silver Clusters: Structural and Topological (ELF, QTAIM) Analyses.

Amine ligands are expected to drive the organization of metallic centers as well as the chemical reactivity of silver clusters early growing during the very first steps of the synthesis of silver nanoparticles via an organometallic route. Density functional theory (DFT) computational studies have been performed to characterize the structure, the atomic charge distribution, and the planar two-dimensional (2D)/three-dimensional (3D) relative stability of small-size silver clusters (Agn, 2 ≤ n ≤ 7), with or without an ethylamine (EA) ligand coordinated to the Ag clusters. The transition from 2D to 3D structures is shifted from n = 7 to 6 in the presence of one EA coordinating ligand, and it is explained from the analysis of the Ag-N and Ag-Ag bond energies. For fully EA saturated silver clusters (Agn-EAn), the effect on the 2D/3D transition is even more pronounced with a shift between n = 4 and 5. Subsequent electron localization function (ELF) and quantum theory of atoms in molecules (QTAIM) topological analyses allow for the fine characterization of the dative Ag-N and metallic Ag-Ag bonds, both in nature and in strength. Electron transfer from ethylamine to the coordinated silver atoms induces an increase of the polarization of the metallic core.

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 qXn- (n = 1 or 2) for its derivatives. The formation energies of the Alq3 and Al(qX)3 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 qXn- (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 qXn- (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 qXn- (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.