Koichiro Takao

This Forum Article provides an overview of the reported studies on the actinide chemistry in ionic liquids (ILs) with a particular focus on several fundamental chemical aspects: (i) complex formation, (ii) electrochemistry, and (iii) extraction behavior. The majority of investigations have been dedicated to uranium, especially for the 6+ oxidation state (UO2(2+)), because the chemistry of uranium in ordinary solvents has been well investigated and uranium is the most abundant element in the actu

The molecular structures of UO2(salophen)L (L = DMF, DMSO) and a uranyl-salophen complex without any unidentate ligands (L) in solid and solution were investigated using single-crystal X-ray analysis and IR, 1H NMR, and UV-visible absorption spectroscopies. As a result, it was found that the uranyl-salophen complex without L is a racemic dimeric complex, [UO2(salophen)]2, in which the UO2(salophen) fragments are held together by bridging between one of the phenoxide oxygen atoms in salophen and

The U(VI) complex with a pentadentate Schiff base ligand (N,N'-disalicylidenediethylenetriaminate = saldien(2-)) was prepared as a starting material of a potentially stable U(V) complex without any possibility of U(V)O(2)(+)...U(V)O(2)(+) cation-cation interaction and was found in three different crystal phases. Two of them had the same composition of U(VI)O(2)(saldien) x DMSO in orthorhombic and monoclinic systems (DMSO = dimethyl sulfoxide, 1a and 1c, respectively). The DMSO molecule in both 1

Complexation of Np(IV) with several carboxylates (RCOO(-); R = H, CH(3), or CHR'NH(2); R' = H, CH(3), or CH(2)SH) in moderately acidic aqueous solutions was studied by using UV-vis-NIR and X-ray absorption spectroscopy. As the pH increased, all investigated carboxylates initiated formation of water-soluble hexanuclear complexes, Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4), in which the neighboring Np atoms are connected by RCOO(-)syn-syn bridges and the triangular faces of the Np(6) octahedron are

The structures of three different U(V) complexes, [U(V)O(2)(salophen)DMSO](-), [U(V)O(2)(dbm)(2)DMSO](-), and [U(V)O(2)(saldien)](-), in a dimethyl sulfoxide (DMSO) solution were determined by X-ray absorption fine structure for the first time.

Molecular and crystal structures of UO2(NO3)2(NRP)2 (NRP = N-alkylated 2-pyrrolidone derivative) have been investigated by using single crystal X-ray analysis. All UO2(NO3)2(NRP)2 complexes have typical structural properties of UO2(NO2)2(L)2 (L = unidentate ligand), i.e., hexagonal-bipyramidal geometry, two NRP and two NO3− located in trans positions in an equatorial plane of the uranyl moiety, U═Oyl ≃ 1.76 Å, U−ONRP = 2.38−2.41 Å, U−ONO3 = 2.50−2.54 Å, and a bond angle between the U−ONRP bond a

Stability and coordination of neptunyl(VI) and -(V) acetate complexes in aqueous solution were studied by using UV-vis-near-IR (NIR) and X-ray absorption fine structure (XAFS) spectroscopy. In the neptunyl(VI) acetate system, the formation of Np(VI)O(2)(AcO)(+), Np(VI)O(2)(AcO)(2)(aq), and Np(VI)O(2)(AcO)(3)(-) was detected. Both spectroscopic methods provided similar stability constants: log K(1) = 2.98 +/- 0.01, log beta(2) = 4.60 +/- 0.01, and log beta(3) = 6.34 +/- 0.01 from UV-vis-NIR and l

Redox behavior of [UO2(gha)DMSO](-)/UO2(gha)DMSO couple (gha = glyoxal bis(2-hydroxanil)ate, DMSO = dimethyl sulfoxide) in DMSO solution was investigated by cyclic voltammetry and UV-vis-NIR spectroelectrochemical technique, as well as density functional theory (DFT) calculations. [UO2(gha)DMSO](-) was found to be formed via one-electron reduction of UO2(gha)DMSO without any successive reactions. The observed absorption spectrum of [UO2(gha)DMSO](-), however, has clearly different characteristic

While one should be aware that its zero CO₂ emission is actually achievable only when electric power is generated, nuclear power is one of the most viable and proven "carbon-free" energy sources to provide baseload electricity to the current energy-demanding society. Even after the power generation, the major part of spent nuclear fuels still consists of recyclable nuclear fuel materials such as U and Pu, promising circular economy of nuclear energy systems in principle. However, actu

Oxygenation reaction of cyclohexene was studied under the presence of a fourfold UO22+ complex with cyclohexyldiphenylphosphine oxide, [UO2(OPCyPh2)4]2+, and blue light irradiation at 436 nm in acetonitrile. As a result, 1,6-hexanedial, cyclohexene oxide, 2-cyclohexen-1-one, and 2-cyclohexen-1-ol were photocatalytically generated as oxygenated products with turnover frequency = 6.7 h–1. In contrast, dimerization of cyclohexene was observed under Ar atmosphere. This implies that a hydrogen atom a

Uranyl(VI) complexes with pentadentate N₃O₂-donating Schiff base ligands having various substituents at the <i>ortho</i> (R₁) and/or <i>para</i> (R₂) positions on phenolate moieties, R₁,R₂-^Mesaldien^2-, were synthesized and thoroughly characterized by ¹H nuclear magnetic resonance, infrared, elemental analysis, and single-crystal X-ray diffraction. Molecular structures of UO₂(R<sub>1</sub

In the crystal structure of the title compound, [U(2)(NO(3))(2)O(4)(O(2))(C(4)H(7)NO)(4)], two UO(2) (2+) ions are connected by a μ-η(2):η(2)-O(2) unit. The O(2) unit shows 'side-on' coordination to both U atoms. An inversion center is located at the midpoint of the O-O bond in the O(2) unit, affording a centrosymmetrically expanded dimeric structure. The U-O(axial) bond lengths are 1.777 (4) Å and 1.784 (4) Å, indicating that the oxidation state of U is exclusively 6+, i.e., UO(2) (2+). Further

Uranyl(<sc>vi</sc>) ion is a strongly hard Lewis-acid and plays a catalytic role in the nucleophilic acyl substitution of acid anhydrides.

The solubility of UO2(NO3)2(NRP)2 (NRP = N-alkyl-2-pyrrolidone) in aqueous solutions with HNO3 (0–5.0 M) and the corresponding NRP (0–0.50M) has been studied. As a result, the solubility of each speciesof UO2(NO3)2(NRP)2 generally decreases with increasing concentrations of HNO3 and the corresponding NRP (C HNO3 and C NRP, respectively) in the supernatant. The solubility of UO2(NO3)2(NRP)2 also depends on the type of NRP; a higher hydrophobicity of NRP generally leads to a lower solubility of UO

Nuclear fuel recycling is one of promising options to resolve current issues arising from energy security and nuclear wastes. Chemical separation called reprocessing aims to recover recyclable nuclear fuel materials from spent fuels, and also to reduce the volume of high‐level radioactive wastes. Even today, solvent extraction is extensively employed as a principal method for reprocessing, while there are also several safety and security concerns arising from use of large amount of organic solve