The complexation of U(IV) ion with N, N, N′, N′-Tetraalkyl-Diglycolamide in aqueous solutions and extraction systems of varying anions

A computational study on the coordination modes and electron absorption spectra of the complexes U(iv) with N,N,N′,N′-tetramethyl-diglycolamide and anions

“…Moreover, the different spectral performance in HCl and HNO 3 and the diffusion reflectance spectrum is attributed to the influence of counterions, who are hypothesized to appear in the inner coordination sphere. 1 This finding contradicts the previous experimental results that the NO 3 − counterion is demonstrated to only appear in the outer coordination sphere and not directly bond with Pu( iv ) in the 1 : 3 complex of TMGDA-Pu( iv ) based on the vis-NIR spectra and crystal structures. 28 Therefore, whether the counterions will exist in the first coordination sphere and how they will influence the extraction needs a deep analysis.…”

“…† The structure of bare U( iv )–TMDGA is directly provided by the experiment. 1 It should be noted that, the optimization is performed with C, O and U atoms fixed in bare U( iv )–TMDGA system to maintain the experimental condition and release all atoms in other self-built structures. For H 2 O–U( iv )–TMDGA complex, the molecule of water is pushed away from the inner coordination sphere during the optimization, due to the uncompetitive inter-molecular interaction and strong steric-hindrance effect.…”

“…Meanwhile, geometric optimization, molecular dynamics and binding energy simulation demonstrates its behaviour. Further, under the guidance of experiments and our recent research findings, 1,46 we take use of absorption spectra as a tool to deeply investigate the underlying mechanism for counterions coordinated with U( iv )–TMDGA complex. It is worth mentioning that, Lan et al summarized 11 distinguished computation methods to mimic the absorption spectrum of hydrated tetravalent uranium and pointed out that, the complete active space self-consistent field (CASSCF) integrating n-electron valence state perturbation theory (NEVPT2), combining with Douglas–Kroll–Hess (DKH) method and spin–orbit coupling (SOC) effect can accurately describe the characteristics of the excited states of actinides and the electron transitions between them.…”

“…Actually, the absolute position of each peak cannot be simulated exactly, but compared with the non-ligand U(IV)-TMDGA complex, the complexes with counterions all show a slightly blue shi, which is in agreement with the experiment. 1 Table 3 The summarized binding energy (BE) for U(IV)-TMDGA with the inserted counterions and the water molecular. Amongst, only one Cl − , NO 3 − and water is considered, with two types of NO 3 − ligand (monodentate and bidentate).…”

“…Amongst, the 2.40 Å in pure U(IV)-TMDGA is determined by experiments. 1 When a Cl − is inserted, the TMDGA ligands are pushed away from the centered U atom, with the averaged bond length at 2.51 Å. Aer optimization, the mono-type shows a smaller U-O bond length even than Cl − , while bi-type shows a little bit longer bond length due to its requirement of space. Actually, the 0.05 Å difference may not have huge inuence on their stability.…”