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Exploring the Hydration of Pb2+: Ab Initio Studies and First-Principles Molecular Dynamics

Authors

  • Christophe Gourlaouen Ing.,

    1. Université Pierre et Marie Curie - Paris 6, Laboratoire de Chimie Théorique, UMR 7616, CC 137, 4 place Jussieu, 75252 Paris Cedex 05, France, CNRS, UMR 7616, 75005 Paris, France, Fax: (+33) 144-275-526, Fax: (+33) 144-274-117
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  • Hélène Gérard Dr.,

    1. Université Pierre et Marie Curie - Paris 6, Laboratoire de Chimie Théorique, UMR 7616, CC 137, 4 place Jussieu, 75252 Paris Cedex 05, France, CNRS, UMR 7616, 75005 Paris, France, Fax: (+33) 144-275-526, Fax: (+33) 144-274-117
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  • Olivier Parisel Dr.

    1. Université Pierre et Marie Curie - Paris 6, Laboratoire de Chimie Théorique, UMR 7616, CC 137, 4 place Jussieu, 75252 Paris Cedex 05, France, CNRS, UMR 7616, 75005 Paris, France, Fax: (+33) 144-275-526, Fax: (+33) 144-274-117
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Abstract

Even though lead is a well-known toxicant widely scattered throughout the world since antiquity, its chemistry is poorly documented at the molecular level. Here we investigate the hydration of the Pb2+ ion by means of first-principles molecular dynamics (Car–Parrinello molecular dynamics, CPMD). We found that the hydrated cation is heptacoordinated in a dynamically holodirected arrangement roughly corresponding to a fluxional distorted pentagonal bipyramid. The time-averaged Pb[BOND]O bond length is especially large and amounts to 2.70 Å with an associated root-mean-square deviation of 0.26 Å. This results from a dynamic exchange between short (<2.6 Å), intermediate (2.6–3.0 Å) and long (>3.0 Å) Pb[BOND]O bonds. The latter very long Pb[BOND]O distance implies that the determination of the coordination number nc from experimental work may not necessarily yield values directly comparable to the theoretical value of nc=7, since not all experimental techniques would recognize such a long distance as a bond to the metal cation. Pronounced disorders are evidenced in the second shell, characteristic of a chaotropic cation, and exchanges between the first and second shells cannot be excluded on a timescale of a few tens of picoseconds.

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