Effect of tris(acetylacetonato)chromium(III) as a complex ligand on the extraction of lanthanoid(III) with 2-thenoyltrifluoroacetone

Enhancement of the extraction of lanthanoid(III) (Ln) with 2-thenoyltrifluo roacetone (Htta) in cyclohexane or benzene has been observed by the additio n of tris(acetylacetonato)chromium(III) (Cr(acac)(3)). The equilibrium anal ysis suggested that the effect of Cr(acac)(3) could be ascribed to the form ation of a 1:1 adduct of Ln(tta)(3) with Cr(acac)(3), i.e., a bi-nuclear co mplex, in the organic phase. The formation constants (beta (s,i)) of the ad ducts were determined across the Ln series. The A,, values decreased with d ecrease in the ionic radii of Ln in the light Ln, and were constant in the heavy Ln. Spectroscopic studies such as electronic absorption, IR, and H-1 NMR were performed to explain the difference between the light and heavy Ln . The adduct of light Ln is mainly an inner sphere complex in which Cr(acac )(3) displaces the coordinated water of the Ln chelate and directly coordin ates to the Ln ion. On the other hand, the adduct of heavy Ln is an outer s phere complex formed by the hydrogen bonding between Cr(acac)(3) and the co ordinated water of the Ln chelate. Abilities of Cr(acac)(3) as a complex li gand, i.e., the basicity and the steric factor, were evaluated by comparing with Co(acac)(3) reported previously.