Variation of the Solvation Number of Eu(III) in Mixed System of Methanol and Water

Abstract

Europium / Mixed solvent / Stability constant / Monofluoride complex / Variation in solvation number SummaryThe stability constants (/?,) of the monofluoride complex of Eu(IlI) have been determined in mixed solvents of methanol and water at a 0.10 Μ ionic strength using a solvent extraction technique. The values of In /?, increase as the mole fraction of methanol in the mixed solvent system increases. The variation in the stability constants can be correlated with both the large effect due to the solvation of F" and the small effect due to both (1) the solvation of cations in connection with complexation and (2) the electrostatic attraction between Eu lT and F . Based on the variation in the sum of (1) and (2) in water and the mixed solvent solutions, it was determined that the coordination number (CN) of Eu(III) varied from a mixture of CN = 9 and 8 to CN = 8 at about a 0.03 mole fraction of methanol in the mixed solvent.

An inflection point in the solvation number around Sm3+ in the mixed system of methanol and water

“…It was also examined by SUGANUMA et al that the X s value for the inflection point of CN around Eu 3+ in the 0.10M ionic strength solution was about 0.03. 7 Since the mean hydration number of Sm 3+ (about 8.8) is larger than that of Eu 3+ (about 8.3) I-3 and the radii in CN=9 and 8 of Sm 3+ are also larger than those of Eu3+, 14 it is reasonable that the X s value (+0.06) for the inflection point of Sm(III) is somewhat higher than that (+0.03) of Eu(III).…”

“…SUGANUMA et al examined the variation in the solvation number of the primary solvation sphere of Eu 3+ in the mixed CH3OH+H20 solution using two different methods. 7,8 One was done based on the variation in the stability constant of EuF 2+ forming a contact ion -air and the other based on the variation in the stability constant of EuC12+ forming a solvent-shared ion -air The X s value (.-'0.03) of the inflection point for the variation in a mixture of CN = 9 and 8 to CN = 8 on the solvation number around Eu 3+, based on the stability constant of EuF 2+, was determined by the variation in the sum of (1) the cation solvation effect (-Ag/RT) employed by us 9 and (2) the electrostatic attraction between Eu 3+ and F-in H20 and the mixed CH3OH+H20 solvent solutions (Agv/RT). The X s value (+0.014) of the inflection point for the variation in the distance between Eu 3+ and C1-in the mixed solvent system was estimated using the Born-type equation 1~ and the Gibbs free energy derived from the stability constant of EuCI 2+.…”