Nine-coordinate adducts of tetrakis(thenoyltrifluoroacetonato)uranium(IV): equilibrium constants from 1H NMR and electronic spectroscopy

Abstract

Time-averaged chemical shifts in the 1H NMR spectra of aniline, pyridine and some derivatives, induced by coordination in 1:1 complexes to the paramagnetic 5 f 2 uranium(IV) as its complex with the thenoyltrifluoroacetonato anion [U(TTA) 4], have been used to find equilibrium constants in benzene and acetone solution. The bound chemical shifts are shown to be solvent independent. In acetone the equilibrium constant for the formation ofU(TTA) 4·H 2O was found to be 4.0±0.2 dm 3 mol −1 from 1H NMR spectroscopy. Equilibrium constants have also been determined by electronic spectroscopy in benzene solution, in which U(TTA) 4 itself is eight-coordinate. The results were correlated with the basicity of the substrate and the effects of steric hindrance were evaluated. U(TTA) 4 is nine-coordinate in acetone through solvent coordination and the addition of substrate caused no or small changes to the electronic spectrum.