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The chemistry of divalent lanthanides, Ln 2+ , is a growing sub-field of heavy element chemistry owing to new synthetic approaches. However, some theoretical aspects of these unusual cations are currently underdeveloped, especially as they relate to their dynamic properties in solution. In this work, we address the hydration of two of the classical Ln 2+ cations, Sm 2+ and Eu 2+ , using atomic multipole optimized energetic for biomolecular applications (AMOEBA) force fields. These cations have not been parameterized to date with AMOEBA, and few studies are available because of their instability with respect to oxidation in aqueous media. Coordination numbers (CN's) of 8.2 and 8.1 respectively for Sm 2+ and Eu 2+ , and 8.8 for both Sm 3+ and Eu 3+ have been obtained and are in good agreement with the few available AIMD and X-ray absorption fine structures studies. The decreased CN of Ln 2+ compared with Ln 3+ arises from progressive water exchange events that indicates the gradual stabilization of 8-coordinate structures with respect to 9-coordinate geometries. Moreover, the effects of the chloride counter anions on the coordination of Ln 2+ cations have been studied at different chloride concentrations in this work. Lastly, water exchange times of Ln 2+ cations have been calculated to provide a comprehensive understanding of the behavior of Eu 2+ and Sm 2+ in aqueous chloride media., (© 2022 Wiley Periodicals LLC.)

There is significant interest in ligands that can stabilize actinide ions in oxidation states that can be exploited to chemically differentiate 5f and 4f elements. Applications range from developing large-scale actinide separation strategies for nuclear industry processing to carrying out analytical studies that support environmental monitoring and remediation efforts. Here, we report syntheses and characterization of Np(iv), Pu(iv) and Am(iii) complexes with N-tert -butyl- N -(pyridin-2-yl)hydroxylaminato, [2-( t BuNO)py] - (interchangeable hereafter with [( t BuNO)py] - ), a ligand which was previously found to impart remarkable stability to cerium in the +4 oxidation state. An[( t BuNO)py] 4 (An = Pu, 1 ; Np, 2 ) have been synthesized, characterized by X-ray diffraction, X-ray absorption, 1 H NMR and UV-vis-NIR spectroscopies, and cyclic voltammetry, along with computational modeling and analysis. In the case of Pu, oxidation of Pu(iii) to Pu(iv) was observed upon complexation with the [( t BuNO)py] - ligand. The Pu complex 1 and Np complex 2 were also isolated directly from Pu(iv) and Np(iv) precursors. Electrochemical measurements indicate that a Pu(iii) species can be accessed upon one-electron reduction of 1 with a large negative reduction potential ( E 1/2 = -2.26 V vs. Fc +/0 ). Applying oxidation potentials to 1 and 2 resulted in ligand-centered electron transfer reactions, which is different from the previously reported redox chemistry of U IV [( t BuNO)py] 4 that revealed a stable U(v) product. Treatment of an anhydrous Am(iii) precursor with the [( t BuNO)py] - ligand did not result in oxidation to Am(iv). Instead, the dimeric complex [Am III (μ 2 -( t BuNO)py)(( t BuNO)py) 2 ] 2 ( 3 ) was isolated. Complex 3 is a rare example of a structurally characterized non-aqueous Am-containing molecular complex prepared using inert atmosphere techniques. Predicted redox potentials from density functional theory calculations show a trivalent accessibility trend of U(iii) < Np(iii) < Pu(iii) and that the higher oxidation states of actinides ( i.e. , +5 for Np and Pu and +4 for Am) are not stabilized by [2-( t BuNO)py] - , in good agreement with experimental observations., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The activation of U-N multiple bonds in an imido analogue of the uranyl ion is accomplished by using a system that is very electron-rich with sterically encumbering ligands. Treating the uranium(VI) trans -bis(imido) UI 2 (NDIPP) 2 (THF) 3 (DIPP = 2,6-diisopropylphenyl and THF = tetrahydrofuran) with tert -butyl(dimethylsilyl)amide (NTSA) results in a reduction and rearrangement to form the uranium(IV) cis -bis(imido) [U(NDIPP) 2 (NTSA) 2 ]K 2 ( 1 ). Compound 1 features long U-N bonds, pointing toward substantial activation of the N═U═N unit, as determined by X-ray crystallography and 1 H NMR, IR, and electronic absorption spectroscopies. Computational analyses show that uranium(IV)-imido bonds in 1 are significantly weakened multiple bonds due to polarization toward antibonding and nonbonding orbitals. Such geometric control has important effects on the electronic structures of these species, which could be useful in the recycling of spent nuclear fuels.