The Coordination Number of Lu(III) in a Mixed System of Methanol and Water

Abstract

The stability constants (β1(F)) of the monofluoro complex of Lu(III) and those (β1(Cl)) of the monochloride solvent-shared ion-pair of Lu(III) have been determined in mixed solvents of methanol and water at 0.10 and 1.00 mol·dm−3 ionic strengths, respectively. The variation in lnβ1(F) with an increase in the mole fraction of methanol (X s) in the mixed solvent system showed an acute-angled convex inflection point at X s ≈ 0.12, an acute-angled concave inflection point at X s ≈ 0.22, and another acute-angled convex inflection point at X s ≈ 0.27. It was concluded that the first and the second convex inflection points denoted the CN of Lu3+ from CN = 8 to a mixture of CN = 8 and 7 and from CN = 8 and 7 to a mixture containing CN = 6, respectively. The concave point is the starting point of a change in the CN of Lu(III) in LuF2+ from CN = 8 to a mixture of CN = 8 and 7. The values of two inflection points of the CN around Lu3+ are consistent with the inflection points of the variation in the values of lnβ1(Cl) versus the dielectric constant of the mixed solvent.