HYDRATION OF IONS IN ORGANIC-SOLVENT AND ITS SIGNIFICANCE IN THE GIBBS ENERGY OF ION TRANSFER BETWEEN 2 IMMISCIBLE LIQUIDS

Various kinds of cations (alkali and alkaline earth metal ions, Me4N+, Et4N+, n-Bu4N+, and tetraphenylarsonium ion) and anions (halide ions, SCN-, ClO4-, NO3-, and tetraphenylborate ion) have been extracted fro m water to nitrobenzene (NB) using several extractants: viz. tetraphen ylborate and dipicrylaminate for the cations; n-Bu4N+, n-Pen(4)N(+), n -Hep(4)N(+), and tris(1,10-phenanthroline)iron(II) for the anions. The determination of water content in NE by means of the Karl Fischer met hod has confirmed that some water molecules are coextracted by hydroph ilic inorganic cations and anions. Accurate numbers (n) of the coextra cted water molecules per ion have been established. On the basis of th ese findings, a new model has been proposed for a better understanding of the Gibbs energy (Delta G(tr)(oO-->W)) of ion transfer at the orga nic solvent/water interface. If hydrated radii of ions evaluated from n are used, conventional (Born-type) electrostatic solvation models ar e invalid. A new approach recognizing short-range ion-solvent interact ions (e.g. hydrogen bonds) has given a better account of Delta G(tr)(o O-->W) for the hydrated ions.