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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, LI) is studied by spectrophotometric titrations and single crystal X-ray diffraction. Three successive complex species, [AmLI]3+, [AmLI2]3+, and [AmLI3]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 LI at 25 °C in 1 M NaNO3. Single crystals of AmLI3(ClO4)3 have been grown from a HClO4 solution containing Am3+ and LI. The crystal structure of AmLI3(ClO4)3 shows that Am(III) is coordinated by nine oxygen atoms from three LI ligands. The deconvoluted UV-Vis absorption spectrum of [AmLI3]3+ in aqueous solution is nearly identical to the diffusion reflectance spectrum of AmLI3(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, LII) is also prepared and studied using spectrophotometry. The similarity in UV-Vis absorption of the extracted complex of Am(III) with LII and [AmLI3]3+ suggests that the Am(III) ion is also coordinated by three tridentate LII ligands existing as [AmLII3]3+ in the organic phase of solvent extraction.
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