Ion solvation and association and water structure in an aqueous cerium (III) chloride solution in the gigapascal pressure range.

X-ray diffraction measurements are performed on a 1 m (= mol kg-1) CeCl3 aqueous solution over a temperature range of 300-600 K and a pressure range of 0.1 MPa to 4 GPa. The experimental interference functions are analyzed by an empirical potential structure refinement (EPSR) modeling. The Ce3+ coordinates water molecules in a tricapped trigonal prism configuration under the ambient condition. The number of water molecules around Ce3+ changes from 8.8 at 0.1 MPa/300 K to 11.5 at 4 GPa/600 K. The number of water molecules around Cl- changes drastically from 10 under the ambient condition to 17 at 4 GPa/600 K. The tetrahedral-like network structure of water under the ambient condition is transformed toward a simple liquid-like packing in the GPa pressure range. The corresponding coordination number is increased from 4.3 in the ambient condition to 9.7 at 4 GPa/600 K. The Ce3+-Cl- association decreases with increasing pressure.