title: Revisiting H2O Nucleation around Au+and Hg2+: The Peculiar "Pseudo-Soft" Character of the Gold Cation.
abstract: In this contribution, we propose a deeper understanding of the electronic effects affecting the nucleation of water around the Au+and Hg2+metal cations using quantum chemistry. To do so, and in order to go beyond usual energetical studies, we make extensive use of state of the art quantum interpretative techniques combining ELF/NCI/QTAIM/EDA computations to capture all ranges of interactions stabilizing the well characterized microhydrated structures. The Electron Localization Function (ELF) topological analysis reveals the peculiar role of the Au+ outer-shell core electrons (subvalence) that appear already spatially preorganized once the addition of the first water molecule occurs. Thus, despite the addition of other water molecules, the electronic structure of Au(H2O)+appears frozen due to relativistic effects leading to a maximal acceptation of only two waters in gold's first hydration shell. As the values of the QTAIM (Quantum Theory of Atoms in Molecules) cations's charge is discussed, the Non Covalent Interactions (NCI) analysis showed that Au+appears still able to interact through longer range van der Waals interaction with the third or fourth hydration shell water molecules. As these types of interaction are not characteristic of either a hard or soft metal cation, we introduced the concept of a "pseudo-soft" cation to define Au+behavior. Then, extending the study, we performed the same computations replacing Au+with Hg2+, an isoelectronic cation. If Hg2+behaves like Au+for small water clusters, a topological, geometrical, and energetical transition appears when the number of water molecules increases. Regarding the HSAB theory, this transition is characteristic of a shift of Hg2+from a pseudosoft form to a soft ion and appears to be due to a competition between the relativistic and correlation effects. Indeed, if relativistic effects are predominant, then mercury will behave like gold and have a similar subvalence/geometry; otherwise when correlation effects are predominant, Hg2+behaves like a soft cation.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France ; CNRS, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France ; Department of Chemistry, Duke University , Durham, North Carolina 27708, United States.
authors.forename: Robin
authors.initials: R
authors.lastname: Chaudret
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France ; CNRS, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France.
authors.forename: Julia
authors.initials: J
authors.lastname: Contreras-Garcia
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France ; CNRS, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France ; Department of Chemistry - Uppsala University , Ångström Laboratory, Theoretical Chemistry, Ångströmlaboratoriet Lägerhyddsvägen 1751 20 Uppsala, Sweden.
authors.forename: Mickaël
authors.initials: M
authors.lastname: Delcey
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France ; CNRS, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Parisel
authors.affiliation: Department of Chemistry, Duke University , Durham, North Carolina 27708, United States.
authors.forename: Weitao
authors.initials: W
authors.lastname: Yang
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France ; CNRS, UMR 7616 , Laboratoire de Chimie Théorique, case courrier 137, 4 place Jussieu, F-75005, Paris, France.
authors.forename: Jean-Philip
authors.initials: JP
authors.lastname: Piquemal