Equilibrium and spectroscopic studies on the complexation of tris(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)lanthanoids(III) with tris (2,4-pentanedionato)cobalt(III) as complex ligand

Complexation equilibrium between tris(1-(2-thienyl)-4,4,4-trifluoro-1,3-but anedionato) lanthanoids(III) (Ln(tta)(3), Ln = La, Eu, and Lu) and tris(2,4 -pentanedionato)cobalt(III) (Co(acac)(3)) has been studied by the liquid-li quid distribution technique. A 1:1 adduct of [Ln(tta)(3)Co(acac)(3)], i.e., a binuclear complex, was formed in benzene, and the stability constants we re determined to be 10(4.64), 10(2.95), and 10(2.07) for La, Eu, and Lu res pectively. The molar absorptivity of Co(acac)(3) for the T-1(1g) <-- (1)A(1 g) transition increased with the adduct formation with Ln(tta)(3) in the or der of Lu << Eu < La. A Co-59 NMR study showed that a resonance of Co(acac) (3) shifted to the higher field with the adduct formation. The chemical exc hange between free and complexed Co(acac)(3) was very slow in La but fast i n Lu, while both the slow- and fast-exchange species existed in Eu. (C) 199 9 Elsevier Science S.A. All rights reserved.