Cation, actinide, hydration sphere

Hydration and Pu oxidation states. 216-29 Hydration sphere, actinide cation and... 

Bulk data of solvation of tetravalent cations supports octa-coordination in the first hydration sphere whereas the actinyl(VI) cations seem to favor hexa-coordination in the plane perpendicular to the axial actinyl group. The trends in the thermodynamic parameters of hydration across the actinide series are essentially similar to those observed for the lanthanide ions and the small differences can be attributed to relativistic effects in the actinides which causes changes in the relative energies of the s, p, d, and f orbitals. 

There is not much information on the hydration of these trivalent cations. Estimates made on the basis of the calculated entropies of hydration suggest a hydration number of about 7 (5, 6a). But an estimate made by extrapolation of data for electrophoretic transport measurements on the ions of some heavier actinides indicate a hydration number of about 12.7, with nine water molecules in the first coordination sphere (66),... 

---