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-butanedionato) 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-liquid 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 were determined to be 10(4.64), 10(2.95), and 10(2.07) for La, Eu, and Lu respectively. The molar absorptivity of Co(acac)(3) for the T-1(1g) <-- (1)A(1g) transition increased with the adduct formation with Ln(tta)(3) in the order 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 exchange between free and complexed Co(acac)(3) was very slow in La but fast in Lu, while both the slow- and fast-exchange species existed in Eu. (C) 1999 Elsevier Science S.A. All rights reserved.