Advancing Understanding of the +4 Metal Extractant Thenoyltrifluoroacetonate (TTA^–); Synthesis and Structure of M^IVTTA₄(M^IV= Zr, Hf, Ce, Th, U, Np, Pu) and M^III(TTA)₄^–(M^III= Ce, Nd, Sm, Yb)

Abstract

Thenoyltrifluoroacetone (HTTA)-based extractions represent popular methods for separating microscopic amounts of transuranic actinides (i.e., Np and Pu) from macroscopic actinide matrixes (e.g. bulk uranium). It is well-established that this procedure enables +4 actinides to be selectively removed from +3, + 5, and +6 f-elements. However, even highly skilled and well-trained researchers find this process complicated and (at times) unpredictable. It is difficult to improve the HTTA extraction-or find alternatives-because little is understood about why this separation works. Even the identities of the extracted species are unknown. In addressing this knowledge gap, we report here advances in fundamental understanding of the HTTA-based extraction. This effort included comparatively evaluating HTTA complexation with +4 and +3 metals (M = Zr, Hf, Ce, Th, U, Np, and Pu vs M = Ce, Nd, Sm, and Yb). We observed +4 metals formed neutral complexes of the general formula M(TTA). Meanwhile, +3 metals formed anionic M(TTA) species. Characterization of these M(TTA) ( x = 0, 1) compounds by UV-vis-NIR, IR, H andF NMR, single-crystal X-ray diffraction, and X-ray absorption spectroscopy (both near-edge and extended fine structure) was critical for determining that Np(TTA) and Pu(TTA) were the primary species extracted by HTTA. Furthermore, this information lays the foundation to begin developing and understanding of why the HTTA extraction works so well. The data suggest that the solubility differences between M(TTA) and M(TTA) are likely a major contributor to the selectivity of HTTA extractions for +4 cations over +3 metals. Moreover, these results will enable future studies focused on explaining HTTA extractions preference for +4 cations, which increases from Np to Pu, Hf, and Zr.

Sequestration of tetravalent neptunium from acidic feeds using diglycolamide-functionalized dendrimers in a room temperature ionic liquid: extraction, spectroscopic and electrochemical studies

“…[43][44][45][46] The optical transitions for Np(IV) (f 3 system) are mainly arising from the 4 I 9/2 state to the higher 4 I 11/2 , 4 I 13/2 , 2 G 7/2 , 2 H 9/2 , etc., states. 43,[47][48][49][50] The vis-NIR spectra of the extracted Np-L I and Np-L II complexes look similar in 5% isodecanol +95% n-dodecane medium (Fig. 5(a) and (b)), suggesting a similar ligand environment around Np(IV) in both species in line with the speciation studies performed previously.…”

The coordination chemistry of CmIII, AmIII, and AcIIIin nitrate solutions: an actinide L3-edge EXAFS study

“…These values were impacted marginally by changes in HNO 3 concentration: the inflection points for Cm III were centered around 18 976 eV, for Am III near 18 514 eV, and for Ac III close to 15 875 eV. Based on our previous experience in reproducing actinide L 3 -edge features, 12 , 21 , 34 – 41 uncertainties in edge and peak positions were estimated to be on the order of 0.2 eV. Hence, for a given element (Cm III , Am III , or Ac III ), the 0.05, 4, and 16 M absorption edges and peak positions were nearly equivalent.…”

Bonding Trends in Tetravalent Th–Pu Monosalen Complexes

“…In addition, the tetravalent actinides (An IV ) are the largest series among the early An and have thus already been used to investigate bonding trends [2] to give answers to questions like trends in complex stability, reactivity, or the concept of covalency [2g, 3] . Recently, also fundamental studies on actinide separation [2d] or NMR parameters [4] have confirmed the need of analyzing series of An IV compounds. Besides the actinide center, the ligand choice with its electronic or geometric situation has a huge impact on the complex properties.…”