SOLVENT-EXTRACTION STUDY OF ND3-F-, EU3+-F-, AND TM3+-F- INTERACTION IN MIXED SYSTEM OF DIMETHYL-SULFOXIDE AND WATER()

The stability constants of the monofluoride complex of Nd(III), Eu(III ), and Tm(III) have been determined in mixed solvents of dimethyl sulf oxide (DMSO) and H2O at 0.1 mol dm(-3) ionic strength using a solvent extraction technique. The values for Nd(III) and Eu(III) increase as t he mole fraction of DMSO in the mixed solvent system increases. Howeve r, the stability constant for Tm(III) reaches a maximum in the vicinit y of the mole fraction of DMSO of 0.02 and then decreases. The variati on of the stability constants was equally dependent on following the t wo factors: (1) the Gibbs' free energy of transfer of F- between H2O a nd the mixed solvents; (2) the difference between the solvation energi es of the tripositive cation and of the monofluoride complex in H2O an d the mixed solvent solutions ([Delta G(Ln,solv)(H2O) - Delta G(LnF,so lv)(H2O)] - [Delta G(Ln,solv)(mix) - Delta G(LnF,solv)(mix)]). The dif ference between solvation energies mentioned in (2) was proportional t o the mole fraction of DMSO in the bulk solution and the proportionali ty constant was dependent on a reciprocal of the effective ionic radiu s of the Ln(III).