HYDRATION AND SOLVATION NUMBERS OF ACTINIDE DIOXO CATIONS

Published data on hydration numbers of AnO(2)(+) and AnO(2)(2+) ions i n solutions are discussed. Comparison of the electronic absorption spe ctra of NpO2+ and PuO22+ in perchlorate solutions with the spectra of a series of their crystalline compounds with known crystal structures shows that the actinide coordination polyhedron for both hydrated AnO( 2)(+) and AnO(2)(2+) ions is a pentagonal bipyramid. Spectrophotometri c study also shows that in organic solutions (dimethyl sulfoxide, dime thylformamide, acetone, methanol, acetonitrile, and dioxane) the symme try of the actinide coordination polyhedron for the solvated ions AnO( 2)(+) and AnO(2)(2+) is the same as for aqua complexes, i.e., the solv ation number of these ions is 5. Only in hexamethylphosphoramide- and triphenylphosphine oxide-containing solutions, the centrosymmetric mol ecular complexes of these ions are formed.