LANTHANIDE(III) TRIFLUOROMETHANESULFONATE COMPLEXES IN ANHYDROUS ACETONITRILE

Anhydrous solutions of lanthanide(III) trifluoromethanesulfonates (tri flates) in acetonitrile have been prepared and studied. Solubility mea surements revealed that among the salts considered (Ln(SO3CF3)3; Ln = La-Lu) only the heavier ones (Ln = Dy-Lu) are soluble (S > 150 mmol dm -3) in strictly anhydrous conditions. Additions of small quantities of water proved that the solubility of lighter salts depends strongly on the presence of this reagent in solution. The ability of the triflate ion to coordinate the tervalent lanthanides in anhydrous solutions ha s been investigated by means of conductometric and FT-IR techniques. Q uantitative IR measurements allowed detection of the main species in s olution to be Ln(SO3CF3)2+ and Ln(SO3CF3)3. Their apparent equilibrium constants are reported. The competition of perchlorate and triflate f or the Ln(SO3CF3)2+ ion has also been studied. Measurements of the for mation constant of the mixed complex, Ln(SO3CF3)2ClO4, suggested that the affinity of the perchlorate ion for the Ln(SO3CF3)2+ complex is ab out ten times lower than that of the third triflate. The effects of ad ded water or dimethyl sulfoxide on the dissociation of the triflate co mplexes in AN were also obtained.