Geometric structure of ion hydration shells

Yttrium hydration shell

First hydration shell of the yttrium 3+ cation in aqueous soltuion. The eight water molecules that form the hydration shell adopt the local gemotric structure of a square antiprism.
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Studying ions in solution.

Accurately incorporating short-range structural information into models of liquids and disordered materials is essential for understanding the fundamental mechanisms behind a variety of chemical, biological and physical phenomena. A typical example is the study of ions in solution. Understanding the geometric form of an ion’s hydration shell – the way in which water molecules locally group around the ion in solution – is very important for modelling its chemical activity. We have characterised the structure of the Y3+ cation in dilute YCl3 solution using a combination of different of techniques. Neutron scattering has been employed in conjunction with isotopic substitution of hydrogen for deuterium in the water. This has then been combined with Extended X-ray Absorption Fine Structure (EXAFS) spectral information using computational techniques. The two experimental probes provide markedly different structural sensitivities, and combining them to produce a single structural model has allowed the experimental confirmation of the geometrical form of the cation's hydration shell. The result clearly shows the cation’s preference to be hydrated by eight water molecules adopting a local geometric distribution of a square antiprism.

DT Bowron (ISIS), S Diaz-Moreno (Diamond Light Source)

Contact:  Dr DT Bowron, Daniel.Bowron@stfc.ac.uk

Research date: December 2008

Further Information

DT Bowron and S Diaz-Moreno, J. Phys. Chem. B 111 (2007) 11393

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