![]() Three species of U(IV):L complexes being 1:1, 1:2, and 1:3 (denoted as UL⁴⁺, UL2⁴⁺ and U元⁴⁺) are identified spectroscopically in each of the two different aqueous media, 1 M HCl and 1 M HNO3. ![]() The complexation of U(IV) with N, N, N′, N′-tetramethyl-diglycolamide (TMDGA, L) has been investigated in 1 M HCl and 1 M HNO3 solutions and in a solid compound U元♴(ClO4) formed in aqueous solutions in parallel with that in the extraction system using N, N′-dimethyl-N, N′-dioctyl-diglycolamide (DMDODGA, L′) as extractant. These results indicate that phenanthroline-derived phosphate ligands may serve as promising candidates for separation trivalent actinides over lanthanides from highly active nuclear waste. DFT calculations also suggested that the Am-N bonds in C4-POPhen/Am(III) complexes had higher degree of covalence than the Eu-N bonds in C4-POPhen/Eu(III) complexes, revealing the underlying driven force for the extraction selectivity of Am(III) over Eu(III) by C4-POPhen. The Am(III) complexes exhibited higher complexation ability than those of Ln(III), which was consistent with the extraction results. The stability constants of the C4-POPhen/Am(III) and C4-POPhen/Ln(III) complexes in CH3OH with perchlorate and nitrate were determined by absorption spectroscopy. NMR titration results demonstrated that only 1:1 complex of C4-POPhen with Ln(NO3)3 was formed in CH3OH system, while two complexes (1:1 and 1:2) were found when using Ln(ClO4)3 as the metal salts instead of Ln(NO3)3. The 1:2 metal/ligand complex was the predominant species in extracted organic phase by slope analysis method. Selective extraction of Am(III) over Eu(III) from highly acidic HNO3 solution (up to 3.0 M) with good selectivity and fast extraction rate was achieved by using C4-POPhen ligand. The extraction and complexation of trivalent Am(III) and lanthanide(III) with a new phenanthroline-derived phosphonate ligand, tetrabutyl-(1,10-phenanthrolin-2,9-diyl)phosphonate (C4-POPhen), was investigated by solvent extraction, absorption spectroscopy, NMR titration, luminescence spectroscopy, and theoretical computations. The similarity in UV-Vis absorption of the extracted complex of Am(III) with LII and 3+ suggests that the Am(III) ion is also coordinated by three tridentate LII ligands existing as 3+ in the organic phase of solvent extraction. 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 deconvoluted UV-Vis absorption spectrum of 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. The crystal structure of AmLI3(ClO4)3 shows that Am(III) is coordinated by nine oxygen atoms from three LI ligands. Single crystals of AmLI3(ClO4)3 have been grown from a HClO4 solution containing Am3+ and LI. ![]() ![]() Three successive complex species, 3+, 3+, and 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 ☌ in 1 M NaNO3. Complexation of Am(III) with tetramethyl-3-oxa-glutaramide (TMOGA, LI) is studied by spectrophotometric titrations and single crystal X-ray diffraction.
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