NON-BORNIAN ION SOLVATION ENERGY - AN APPROACH FROM REDOX POTENTIALS OF HETEROPOLY OXOMETALATE ANIONS

The first and second redox potentials (E-1(O) and E-2(O)) of Keggin-ty pe heteropolytungstate anions (alpha-[PW12O40](3-) and alpha-[SiW12O40 ](4-)) have been determined in various solvents by means of cyclic vol tammetry. The difference (Delta E-1,2(O)) between E-1(O) and E-2(O), b eing theoretically associated with the solvation energies of the polya nions, does not correlate with the permittivity of the solvent, in con flict with an expectation based on the Born-type electrostatic solvati on model. In contrast, Delta E-1,2(O), has been found to show some def inite correlations with such empirical solvent parameters as acceptor numbers. This shows that the short-range interactions (i.e., donor-acc eptor effects or hydrogen bonds) between the heteropolyanion and its p rimary solvents play the most significant role in the solvation of the heteropolyanions. We have thus proposed a new analytical equation for evaluating the short-range ion-solvent interaction energy.