Opposite effects of successive hydration shells on the aqua ion structure of metal cations

Elizabeth C. Beret (1) , Elsa Galbis (1) , Rafael R. Pappalardo (1) , Enrique Sanchez Marcos (2)

1 Quimica Fisica
2 Quimica Fisica

The conformation adopted by water molecules around a metal ion in aqueous solution can be approached from a discrete representation of the solvent by studying the structure and stability of microsolvation clusters including a different number of water molecules. In this contribution we present a Quantum Mechanics and ab initio Molecular Dynamics study on how the arrangement of water molecules around Mg2+ and Al 3+ shows preferentially a Th or S6 symmetry depending on the number of hydration shells explicitly included in the calculation. The behavior observed for both cases is the following: a) For a cluster composed of the metal ion plus a first hydration shell the preferred geometry shows a Th symmetry. b) When a second hydration shell is added, a minimum can be found with a S6 disposition of water molecules around the metal center. c) However, if a third hydration shell is considered a Th arrangement of water molecules around the central ion is strongly favored. The structures of the different solvation complexes studied in this work are characterized. The preference for a Th or S6 distribution of water ligands is rationalized in terms of total energies, interaction energies and the hydrogen bond network.

Mots clés: Physical Sciences

Elizabeth C. Beret, Elsa Galbis, Rafael R. Pappalardo, Enrique Sanchez Marcos. Opposite effects of successive hydration shells on the aqua ion structure of metal cations. Molecular Simulation, 2009, 35 (12-13), pp.1007-1014. ⟨10.1080/08927020903033125⟩. ⟨hal-00530456⟩