Interaction of An^VI with Isothiocyanate Ion in Water‐Organic Media (An = U, Np, Pu)

Abstract

Behavior of UVI, NpVI and PuVI in water‐acetonitrile solutions was studied spectrophotometrically with the successive addition of the polar organic ligands (dimethyl sulfoxide or hexamethylphosphoric triamide) and the NCS– ion. The detected spectral effects – changes in the absorption intensity, bathochromic shifts in the absorption bands, the absence of isosbestic points, a change in the color of the solution – indicate complex competitive processes occurring in the studied solutions. In the case of NpVI, its partial reduction to NpIV by NCS– ion is observed. Solid UVI complex, [UO2(HMPA)2(NCS)2], was isolated, its crystal structure was determined using X‐ray diffraction. In contrast to known AnO22+ compounds with the NCS– ion, this complex exhibits tetragonal bipyramidal environment of the U atom. [UO2(HMPA)2(NCS)2] is also characterized by UV/Vis, IR and luminescence spectroscopy.

Neptunium(V) Isothiocyanate Complexes with 4′-Aryl-Substituted 2,2′:6′,2″-Terpyridines and N,N-Dimethylacetamide as Molecular Ligands

“…The choice of the isothiocyanate anion in the studied complexes was based, on the one hand, on the relatively high solubility of neptunium­(V) isothiocyanate in a wide range of organic solvents. On the other hand, it was of interest to check the possibility of utilization of terpyridine derivatives for the extraction of actinide ions not only from nitric acid but also from thiocyanate solutions, in which we could expect significant changes of the extraction characteristics of the metal ions, taking into account that thiocyanate media were studied for many years for possible applications for the separation of trivalent lanthanides and actinides, especially lanthanides and americium-241. − The limitation of the study of thiocyanate media by trivalent actinides is caused by the fact that in aqueous solutions tetravalent plutonium and hexavalent neptunium and plutonium are rapidly reduced to the trivalent plutonium and pentavalent neptunium, respectively, although in nonaqueous media, it is possible to obtain fairly stable isothiocyanate complexes of hexavalent neptunium and plutonium . Np­(IV) and Np­(V) are stable in the presence of thiocyanate ions, and we can expect a significant difference in their behavior during extraction from the thiocyanate solutions at least because of the difference in the stability of the corresponding complexes formed in these solutions.…”

“…37−39 The limitation of the study of thiocyanate media by trivalent actinides is caused by the fact that in aqueous solutions tetravalent plutonium and hexavalent neptunium and plutonium are rapidly reduced to the trivalent plutonium and pentavalent neptunium, respectively, although in nonaqueous media, it is possible to obtain fairly stable isothiocyanate complexes of hexavalent neptunium and plutonium. 40 Np(IV) and Np(V) are stable in the presence of thiocyanate ions, and we can expect a significant difference in their behavior during extraction from the thiocyanate solutions at least because of the difference in the stability of the corresponding complexes formed in these solutions.…”