Complexing ability of the trifluoromethanesulfonate complexes of the heavier lanthanides(III) towards n-butylamine in anhydrous acetonitrile

The thermodynamic parameters for the dissociation in acetonitrile of the tris-trifluoromethanesulfonates of the heavier lanthanides according to the equilibrium Ln(tri)(2)(+) + tri(-) reversible arrow Ln(tri)(3) (Ln = Tb-Lu; tri(-) = CF3SO3-) are reported. Potentiometric, calorimetric, conductometric and FT-IR measurements show that in acetonitrile both Ln(tri)(3) and Ln(tri)(2)(+) form with n-butylamine at least four strong, mononuclear, successive complexes whose stability seems to be not very dependent upon the acceptor charge. The bonding of n-butylamine occurs with a preferential loss of solvent molecules from the coordination sphere of the metal ion rather than with release of triflate ions. The equilibria of formation of ternary complexes Ln(tri)(n)but(m)((3-n)+) (but = n-butylamine; n = 2 or 3; m = 1-4) are qualitatively interpreted in terms of the different factors affecting the ion-ion and ion-dipole interactions. Apparent stability constants and the related thermodynamic values concerning the complexing ability toward n-butylamine of a system containing Ln(tri)(3) and Ln(tri)(2)(+) are given.