Coordination of perchlorate ion in the secondary solvation sphere of Am3+ in the tracer concentrations in mixed system of dimethyl sulfoxide/water with 1.00M (H,Na)(Cl,ClO4)

Abstract

The stability constants, [31, of monochloride complex of Am(Ill) have been determined in a mixed system of dimethyl sulfoxide (DMSO) and water at 1.00 mol.dm -3 ionic strength using solvent extraction. The values of ~t in mixed DMSO+H20 solutions decrease rapidly with an increase in the mole fraction of DMSO (Xs) in mixed solvents and become negative ones, which is not in a definition of stability constant, in Xs>0.04. The variation of [~l in X s <0.02 was accounted for by the size-variation of the primary solvation sphere around Am(Ill), which was present as a solventshared ion-pair, and by a little effect due to an invasion (coordination) of C104-into the secondary solvation sphere of Am 3+. On the other hand, it was concluded that the 1~1 obtained by solvent extraction in X~>0.02 was an apparent value, because of a large effect due to an invasion (coordination) of CIO 4-into the secondary solvation sphere of Am(Ill).