Water-soluble Schiff base-actinyl complexes and their effect on the solvent extraction of f-elements

Abstract

Conventional solvent extraction of neptunyl(v), Cm(iii), Eu(iii) & uranyl(vi) by bis(2-ethylhexylphosphoric acid (HDEHP) can be altered through introduction of an actinyl selective hold-back complexant.

Exploring the Oxidation States of Neptunium with Schiff Base Coordination Complexes

“…Other studies on (Np V O 2 ) + Schiff base complexes typically see this band shift to ∼1000 nm. 20,69,80 However, we note that the use of H 2 salenSO 3 [N,N′-bis(5-sulfanatosalicylidene)] caused a rapid reduction from (Np VI O 2 ) 2+ to (Np V O 2 ) + , 80 whereas Np VI O 2 L(MeOH) displayed only a small amount of reduction to Np IV L 2 . It is also noted that the in situ reduction of Np VI O 2 L(MeOH) gave a spectrum nearly identical to that of a separate sample recorded 1 month after synthesis.…”

Complexation of High-Valency Mid-Actinides by a Lipophilic Schiff Base Ligand: Synthesis, Structural Characterization, and Progress toward Selective Extraction

“…In contrast, we have shown that an aqueous soluble Schiff-base ligand will complex NpO 2 2+ but rapidly reduce it to NpO 2 + . 27 Returning to the tBu-Salen-Np VI system in CH 3 CN, we observe vibrational progression bands between 540 and 650 nm. Such transitions are observed in this region for other Np VI complexes, e.g., [NpO 2 (CO 3 ) 3 ] 4−50 and NpO 2 Cl 2 in THF.…”

“…23−25 In this context, we have previously reported on an aqueous soluble Schiff base that selectively coordinates UO 2 2+ and NpO 2 + in an aqueous phase, yielding separation from a range of trivalent f-element cations. 26,27 We report here synthetic, spectroscopic, crystallographic, and metal-ion-partitioning studies involving a tetradentate, lipophilic Schiff base, N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-ethylenediamine (tBu-Salen; Figure 1), and the hexavalent mid-actinides (UO 2 2+ , NpO 2 2+ , and PuO 2 2+ ).…”

“…Further exploration of the coordination chemistry of the mid-actinide elements (U–Pu) can present the means to a one-step solution to the complete separation of these elements from high-level waste. , In this context, enhanced exploitation of actinide–ligand interactions under nonaqueous conditions is important for the development of biphasic organic–aqueous actinide separation systems, while group extraction of the mid-actinides can also yield enhanced proliferation resistance. − A feature ubiquitous to the mid-actinides (U, Np, and Pu) is the possession of a wide range of accessible oxidation states (+III, +IV, +V and +VI), with the linear dioxoactinyl cation moiety (AnO 2 n + ) dominating the chemistry of the +V and +VI oxidation states. − A multitude of ligand systems have been employed as extractants for biphasic solvent extraction including, but not limited to, organophosphorous compounds, , crown ethers, diglycolamides, − bipyridines, , and Schiff base ligands. − Specifically, multidentate Schiff base ligands provide a framework that can be easily functionalized, possess multiple coordination sites, and can accommodate the steric demands of the linear dioxo moiety. It has been demonstrated that Schiff base ligands can extract UO 2 2+ in liquid–liquid extraction experiments, , as well as stabilize UO 2 + . − In this context, we have previously reported on an aqueous soluble Schiff base that selectively coordinates UO 2 2+ and NpO 2 + in an aqueous phase, yielding separation from a range of trivalent f-element cations. , We report here synthetic, spectroscopic, crystallographic, and metal-ion-partitioning studies involving a tetradentate, lipophilic Schiff base, N , N ′-bis­(3,5-di- tert -butylsalicylidene)-1,2-ethylenediamine ( t Bu-Salen; Figure ), and the hexavalent mid-actinides (UO 2 2+ , NpO 2 2+ , and PuO 2 2+ ).…”

“…Characteristically, the aquo Np VI band at 1223 nm will likely undergo a hypsochromic shift to 1120–1140 nm upon complexation. − This band may be obscured by the intense charge-transfer feature. In addition, a band at 1000 nm has been observed for the main f–f transition in Schiff-base-complexed Np V . , Although it is possible that a transition at 1000 nm may be obscured by the charge-transfer band, a sharp band would likely be observed if there had been a significant reduction of Np VI to Np V . In contrast, we have shown that an aqueous soluble Schiff-base ligand will complex NpO 2 2+ but rapidly reduce it to NpO 2 + .…”