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 t he tris-trifluoromethanesulfonates of the heavier lanthanides accordin g to the equilibrium Ln(tri)(2)(+) + tri(-) reversible arrow Ln(tri)(3 ) (Ln = Tb-Lu; tri(-) = CF3SO3-) are reported. Potentiometric, calorim etric, conductometric and FT-IR measurements show that in acetonitrile both Ln(tri)(3) and Ln(tri)(2)(+) form with n-butylamine at least fou r strong, mononuclear, successive complexes whose stability seems to b e not very dependent upon the acceptor charge. The bonding of n-butyla mine occurs with a preferential loss of solvent molecules from the coo rdination 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 a nd ion-dipole interactions. Apparent stability constants and the relat ed thermodynamic values concerning the complexing ability toward n-but ylamine of a system containing Ln(tri)(3) and Ln(tri)(2)(+) are given.