Infection points in the coordination number around Ce3+ and CeF2+ in a mixed system of methanol and water

The stability constants (beta(1(F))) of the monofluoro complex of Ce(III) a nd those (beta(1(Cl)),) of the monochloride solvent-shared ion-pair of Ce(I II) have been determined in mixed solvents of methanol and water at 0.10 an d 1.00 mol dm(-3) ionic strengths, respectively. The variation in the Ce3+- Cl- distance, which was calculated using the Born-type equation and the Gib bs' free energy derived from beta(1(Cl)), indicated a change in the coordin ation number (CN) of Ce3+ from CN = 9 to a mixture of CN = 9 and 8 in the v icinity of the mole fraction of methanol (X-s) = 0.23. The variation in ln beta(1(F)) with an increase in X-s in the mixed-solvent system showed an ac ute-angled convex inflection point at X-s = about 0.22 and an acute-angled concave inflection point in the vicinity of X-s = 0.28. It was concluded th at the convex inflection point denoted the same change in the CN of Ce3+ fr om CN = 9 to a mixture of CN = 9 and 8, and that the concave point was a ch ange in the CN of Ce(III) in CeF2+ from CN = 9 to a mixture of CN = 9 and 8 .