A structural and spectrophotometric study on the complexation of Am(iii) with TMOGA in comparison with the extracted complex of DMDOOGA

Abstract

Complexation of Am(III) with tetramethyl-3-oxa-glutaramide (TMOGA, L^I) is studied by spectrophotometric titrations and single crystal X-ray diffraction. Three successive complex species, [AmL^I]³⁺, [AmL^I₂]³⁺, and [AmL^I₃]³⁺, have been identified and their stability constants are calculated to be 3.71 ± 0.012, 5.95 ± 0.021, and 6.93 ± 0.034 respectively, from the absorption spectra collected from the titrations of Am(III) with L^I at 25 °C in 1 M NaNO₃. Single crystals of AmL^I₃(ClO₄)₃ have been grown from a HClO₄ solution containing Am³⁺ and L^I. The crystal structure of AmL^I₃(ClO₄)₃ shows that Am(III) is coordinated by nine oxygen atoms from three L^I ligands. The deconvoluted UV-Vis absorption spectrum of [AmL^I₃]³⁺ in aqueous solution is nearly identical to the diffusion reflectance spectrum of AmL^I₃(ClO₄)₃ in the solid state, indicating that the coordination geometry of the complexes is nearly the same. In addition, to provide parallels to solvent exaction, the extracted Am(III) complex with N,N′-dimethyl-N,N′-dioctyl-3-oxa-glutaramide (DMDOOGA, L^II) is also prepared and studied using spectrophotometry. The similarity in UV-Vis absorption of the extracted complex of Am(III) with L^II and [AmL^I₃]³⁺ suggests that the Am(III) ion is also coordinated by three tridentate L^II ligands existing as [AmL^II₃]³⁺ in the organic phase of solvent extraction.