Hydration of some trivalent metal ions extracted as perchlorates with trioctylphosphine oxide in hexane

Perchlorates of Sc³⁺, Y³⁺, La³⁺, and Eu³⁺ have each been extracted from 0.1 mol·dem^?3 aqueous solution of μ□=1 with trioctylphosphine oxide (TOPO) in hexane. The hydration number of the extracted salts has been determined by Karl Fischer titration. Sc³⁺, Y³⁺ and EU³⁺ are extracted as the tetra- and hexa-solvates of TOPO but the assumption of octa-solvate on addition to the tetra-solvate explains the extraction data of La³⁺ well. The hydration number of tetra-solvates is 2 (Sc³⁺ and Eu³⁺), 3 (Y³⁺) and probably 4 for La³⁺ ion. That of hexa- and octa-solvates is 4–5.