Multinuclear NMR Studies on Lewis Acid-Lewis Base Interactions between Bis(pentafluorophenyl)borinic Acid and Uranyl ß-Diketonato Complexes in Toluene.

In order to examine the possibility of Lewis acid-Lewis base (LA-LB) interactions between the boron atom of B(C6F5)2OH and the oxo groups ("yl" oxygen atoms) of uranyl ß-diketonato complexes, we have measured the 1H, 11B, 17O, 19F NMR and IR spectra of toluene solutions containing ß-diketonato complexes [UO2(acac)2DMSO or UO2(dfh)2DMSO, where acac = 2,4-pentanedionate, dfh = 1,1,1,2,2,6,6,7,7,7-decafluoroheptane-3,5-dionate, and DMSO = dimethyl sulfoxide] and B(C6F5)2OH. 11B and 17O NMR spectra of solutions containing UO2(dfh)2DMSO and B(C6F5)2OH showed no change in their chemical shifts regardless of the [B(C6F5)2OH]/[UO2(dfh)2DMSO] ratio. This indicates that there were no apparent interactions between B(C6F5)2OH and UO2(dfh)2DMSO. On the other hand, in the corresponding NMR spectra of solutions containing UO2(acac)2DMSO and B(C6F5)2OH, new signals were observed at a higher field than signals observed in the solutions containing only B(C6F5)2OH or UO2(acac)2DMSO, and their intensity changed with the [B(C6F5)2OH]/[UO2(acac)2DMSO] ratio. These results reveal that a complex with LA-LB interaction (B···O═U) between the boron atom of B(C6F5)2OH and the "yl" oxygen atom of UO2(acac)2DMSO was formed. IR spectra also supported such complex formation; i.e., the asymmetric O═U═O stretching band of UO2(acac)2DMSO was observed to shift from 897 to 810 cm-1 with the addition of B(C6F5)2OH. Moreover, 19F NMR spectra indicated that 1:1 and 2:1 LA-LB complexes exist in equilibrium, UO{OB(C6F5)2OH}(acac)2DMSO + B(C6F5)2OH = U{OB(C6F5)2OH}2(acac)2DMSO. The thermodynamic parameters for this equilibrium were obtained as K = (2.5 ± 0.6) × 102 M-1 (at 25 °C), ΔH = -42.4 ± 5.2 kJ mol-1, and ΔS = -96.7 ± 19.4 J K-1 mol-1. In 1H NMR spectra, the signal due to -CH groups of UO2(acac)2DMSO disappeared, and three signals due to the corresponding -CH groups newly appeared with an increase in the [B(C6F5)2OH]/[UO2(acac)2DMSO] ratio. From these phenomena, it is proposed that 1:1 and 2:1 LA-LB complexes having interactions between the -CH groups of acac and the -OH group of coordinated B(C6F5)2OH are formed depending on the [B(C6F5)2OH]/[UO2(acac)2DMSO] ratio.

Wet chemical processing for nuclear waste glass to retrieve radionuclides.

Here, we show unexpected and significant elution behavior of various elements from simulated nuclear waste glass (NWG) in ∼10° mol dm-3 acidic solutions below 100 °C, where a borosilicate-based glass matrix has been believed to be chemically durable. Most elements like glass main components (Li, B, Na, Ca, Al, and Zn, but except for Si) and simulated radionuclides (Rb, Cs, Sr, Ba, Se, Te, Mn, Pd, Mo, rare earths, Cr, Fe, and Ni) were remarkably eluted from the simulated NWG in ∼10° M HNO3 aq with Cl- at 90 °C. Especially, the elution of Pd is governed by its coordination chemistry including a redox reaction, because Pd(0) present in the simulated NWG has to be oxidized to Pd2+ which forms [PdCl4]2- for its dissolution. While Zr in simulated NWG is sparingly eluted even in this treatment, its elution actually proceeds in 1-3 M H2SO4 aq at 90 °C thanks to strong coordination of Zr(IV) with SO42-. Through design and optimization of the leaching conditions, a protocol of the wet chemical process to retrieve the radionuclides from simulated NWG has been proposed and demonstrated.

Crystal Structure of Regularly Th -Symmetric [U(NO3 )6 ]2- Salts with Hydrogen Bond Polymers of Diamide Building Blocks.

Hexanitratouranate(IV), [U(NO3 )6 ]2- , has been crystallized with anhydrous H+ -involving hydrogen bond polymers connected by selected diamide building blocks. Thanks to the significant moderation of electrostatic interactions between the anions and cations, the molecular structure of [U(NO3 )6 ]2- in these compounds is regularly Th -symmetric. The f-f transitions stemming from 5f2 configuration of U4+ are strictly forbidden by the Laporte selection rule in such a centrosymmetric system, so that the obtained compounds are nearly colourless in contrast to other UIV species usually coloured in green.

Molecular and Crystal Structures of Uranyl Nitrate Coordination Polymers with Double-Headed 2-Pyrrolidone Derivatives.

Double-headed 2-pyrrolidone derivatives (DHNRPs) were designed and synthesized as bridging ligands for the efficient and selective separation of UO22+ from a HNO3 solution by precipitation. The building blocks, UO2(NO3)2 and DHNRPs, were successfully connected to form an infinite 1D coordination polymer. The solubility of [UO2(NO3)2(DHNRP)]n is no longer correlated to the hydrophobicity of the ligand but is exclusively governed by the ligand symmetry and packing efficiency. The newly designed DHNRP family can be used to establish a new spent nuclear fuel reprocessing scheme.

Temperature and Size Effects on Structural and Dynamical Properties of Water Confined in 1 - 10 nm-scale Pores Using Proton NMR Spectroscopy.

We were able to fill 1 - 10 nm-scale silica pores with water by vapor condensation, and examined the freezing phenomena, structures, and molecular motions of the confined water in the temperature range from 293 to 188 K by 1H-NMR spectroscopy. The results showed that almost all water molecules confined in 10 nm-scale pores were frozen and that approximately half of the water confined in 1 nm-scale pores existed in the liquid state even below the freezing point. The water adsorbed on the pore surfaces was estimated as a monolayer in 2.58 nm pores and bi- and tri-layers in 6.48 nm and larger pores, respectively. Furthermore, it was clarified from the proton relaxation rate (1H-1/T1) measurements that the molecular motions of adsorbed water itself were restricted by nanoconfinement and were extremely dependent on the conditions of proton exchange and hydrogen bond rearrangements of the adsorbed water.

Crystal structure of tris-(1,10-phenanthroline-κ(2) N,N')iron(II) bis-[bis-(tri-fluoro-methyl-sulfon-yl)imide] monohydrate.

The crystal structure of the title complex, [Fe(C12H8N2)3][(CF3SO2)2N]2·H2O, is constructed by one octa-hedral [Fe(phen)3](2+) (phen = 1,10-phenanthroline) cation (point group symmetry 2), two Tf2N(-) [bis-(tri-fluoromethyl-sulfon-yl)imide] anions, and one water mol-ecule of crystallization (point group 2). The Fe-N bond lengths are indicative of a d (6) low-spin state for the Fe(II) ion in the complex. The dihedral angle between the phen ligands in the cation is 87.64 (6)°. The Tf2N(-) counter-anion is non-coordinating, with the -CF3 groups arranged in a trans fashion with respect to each other, leading to an anti,anti conformation of the -CF3 groups and -SO2N- moieties relative to the S-C bonds. The water mol-ecule of crystallization connects two O atoms of the Tf2N(-) anions through weak hydrogen bonds. C-H⋯O hydrogen-bonding inter-actions are also observed, consolidating the packing of the mol-ecules into a three-dimensional network structure.

Experimental and theoretical approaches to redox innocence of ligands in uranyl complexes: what is formal oxidation state of uranium in reductant of uranyl(VI)?

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 characteristics from those of uranyl(V) complexes reported so far. Detailed analysis of molecular orbitals and spin density of the redox couple showed that the gha(2-) ligand in UO2(gha)DMSO is reduced to gha(•3-) to give [UO2(gha)DMSO](-) and the formal oxidation state of U remains unchanged from +6. In contrast, the additional DFT calculations confirmed that the redox reaction certainly occurs at the U center in other uranyl(V/VI) redox couples we found previously. The noninnocence of the Schiff base ligand in the [UO2(gha)DMSO](-)/UO2(gha)DMSO redox couple is due to the lower energy level of LUMO in this ligand relative to those of U 5f orbitals. This is the first example of the noninnocent ligand system in the coordination chemistry of uranyl(VI).

Extraction of Pd(II), Rh(III) and Ru(III) from HNO(3) aqueous solution to betainium bis(trifluoromethanesulfonyl)imide ionic liquid.

Extraction efficiencies of Pd(ii), Rh(iii), and Ru(iii) from HNO3(aq) to [Hbet][Tf2N] were demonstrated, i.e., Pd(ii) is the most extractable, Rh(iii) is medium extractable, and Ru(iii) is the least extractable. The extraction seems to proceed through coordination of betaine to the metal ions and the cation exchange of the formed complex with H(+).

Preferential behavior on donating atoms of an ambidentate ligand 2-methylisothiazol-3(2H)-one in its metal complexes.

Five metal complexes of 2-methylisothiazol-3(2H)-one (MIO), [Co(III)(NH3)5(MIO)](3+), [Ru(II)(NH3)5(MIO)](2+), [Ru(III)(NH3)5(MIO)](3+), [Pt(II)Cl3(MIO)](-), and trans-[U(VI)O2(NO3)2(MIO)2], were synthesized, and their structures were determined by single-crystal X-ray crystallography. MIO is an ambidentate ligand and coordinates to metal centers through its oxygen atom in the cobalt(III), ruthenium(III), and uranium(VI) complexes and through its sulfur atom in the ruthenium(II) and platinum(III) complexes. This result suggests that MIO shows preferential behavior on its donating atoms. We also studied the electron-donor abilities of the oxygen and sulfur atoms of MIO. Various physical measurements on the conjugate acid of MIO and the MIO complexes allowed us to determine an acid dissociation constant (pKa) and donor number (DN) for the oxygen atom of MIO and Lever's electrochemical parameter (EL) and a relative covalency parameter (kL) for the sulfur atom.

Uranyl-halide complexation in N,N-dimethylformamide: halide coordination trend manifests hardness of [UO2]2+.

Complexation of [UO2](2+) with Cl(-), Br(-), and I(-) in N,N-dimethylformamide (DMF) was studied by UV-vis absorption spectroscopy and extended X-ray absorption fine structure (EXAFS) to clearly differentiate halide coordination strengths to [UO2](2+). In the Cl(-) system, it was clarified that the Cl(-) coordination to [UO2](2+) in DMF proceeds almost quantitatively. The coordination number of Cl(-) almost quantitatively increases up to 4, i.e., the limiting complex is [UO2Cl4](2-). Logarithmic gross stability constants of [UO2Cl(x)](2-x) (x = 1-4) were evaluated as log ß1 = 9.67, log ß2 = 15.49, log ß3 = 19.89, and log ß4 = 24.63 from UV-vis titration experiments. The EXAFS results well demonstrated not only the Cl(-) coordination, but also the DMF solvation in the equatorial plane of [UO2](2+). The interaction of Br(-) and I(-) with [UO2](2+) in DMF was also investigated. As a result, the Br(-) coordination to [UO2](2+) stops at the second step, i.e., only [UO2Br](+) and UO2Br2 were observed. The molecular structure of each occurring species was confirmed by EXAFS. The evaluated log ßx values of [UO2Br(x)](2-x) (x = 1, 2) are 3.45 and 5.42, respectively. The much smaller log ßx than those of [UO2Cl(x)](2-x) indicates that Br(-) is a much weaker ligand to [UO2](2+) than Cl(-). The EXAFS experiments revealed that the presence of I(-) in the test solution does not modify any coordination structure around [UO2](2+). Thus, I(-) does not form any stable [UO2](2+) complexes in DMF. Consequently, the stability of the halido complexes of [UO2](2+) in DMF is exactly in line with the hardness order of halides.

Actinide chemistry in ionic liquids.

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 actual nuclear fuel cycles. Other actinides such as thorium, neptunium, plutonium, americium, and curiumm, although less studied, are also of importance in fully understanding the nuclear fuel engineering process and the safe geological disposal of radioactive wastes.

Efficient extraction of Rh(III) from nitric acid medium using a hydrophobic ionic liquid.

Rhodium(III) has been successfully extracted from an aqueous nitric acid solution using a hydrophobic ammonium based ionic liquid and CMPO or TODGA as extractant. This result has significant potential for the recovery of rhodium from spent nuclear fuel and thereby increasing the worldwide supply of this rare metal.

Spectroelectrochemical identification of a pentavalent uranyl tetrachloro complex in room-temperature ionic liquid.

Reduction of U(VI)O(2)Cl(4)(2-) in a mixture of 1-ethyl-3-methylimidazolium tetrafluoroborate and its chloride at E°' = -0.996 V vs Fc/Fc(+) and 298 K affords U(V)O(2)Cl(4)(3-), which is kinetically stable and exhibits typical character of U(V) in the UV-vis-NIR absorption spectrum.

The application of novel hydrophobic ionic liquids to the extraction of uranium(VI) from nitric acid medium and a determination of the uranyl complexes formed.

Novel ammonium based hydrophobic ionic liquids (ILs) have been synthesised and characterised, and their use in the liquid-liquid extraction of uranium(VI) from an aqueous nitric acid solution using tri-n-butyl phosphate (TBP), studied. On varying the nitric acid concentration, each IL was found to give markedly different results. Relatively hydrophilic ILs showed high uranium(VI) extractability at 0.01 M nitric acid solution which progressively decreased from 0.01 to 2 M HNO(3) and then increased again as the nitric acid concentration was increased to 6 M. An analysis of the mechanisms involved for one such IL, pointed to cationic-exchange being the predominant route at low nitric acid concentrations whilst at high nitric acid concentrations, anionic-exchange predominated. Strongly hydrophobic ILs showed low extractability for nitric acid concentrations below 0.1 M but increasing extractability from 0.1 M to 6 M nitric acid. The predominant mechanism in this case involved the partitioning of a neutral uranyl complex. The uranyl complexes were found to be UO(2)(2+)·(TBP)(3) for the cationic exchange mechanism, UO(2)(NO(3))(2)(TBP)(2) for the neutral mechanism and UO(2)(NO(3))(3)(-)·(TBP) for the anionic exchange mechanism.

Kinetics and mechanism of permanganate oxidation of iota- and lambda-carrageenan polysaccharides as sulfated carbohydrates in acid perchlorate solutions.

The kinetics of oxidation of iota- and lambda-carrageenan as sulfated carbohydrates by permanganate ion in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm(-3) have been investigated spectrophotometrically. The pseudo-first-order plots were found to be of inverted S-shape throughout the entire courses of reactions. The initial rates were found to be relatively slow in the early stages, followed by an increase in the oxidation rates over longer time periods. The experimental observations showed first-order dependences in permanganate and fractional first-order kinetics with respect to both carrageenans concentration for both the induction and autoacceleration periods. The results obtained at various hydrogen ion concentrations showed that the oxidation processes in these redox systems are acid-catalyzed throughout the two stages of oxidation reactions. The added salts lead to the prediction that Mn(III) is the reactive species throughout the autoacceleration periods. Kinetic evidence for the formation of 1:1 intermediate complexes was revealed. The kinetic parameters have been evaluated and tentative reaction mechanisms in good agreement with the kinetic results are discussed.

7Li NMR studies on complexation reactions of lithium ion with cryptand C211 in ionic liquids: comparison with corresponding reactions in nonaqueous solvents.

(7)Li NMR spectra of DEME-TFSA [DEME=N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium; TFSA=bis(trifluoromethanesulfonyl)amide], EMI-TFSA (EMI=1-ethyl-3-methylimidazolium), MPP-TFSA (MPP = N-methyl-N-propylpyridinium), DEME-PFSA [PFSA=bis(pentafluoroethanesulfonyl)amide], and DEME-HFSA [HFSA=bis(heptafluoropropanesulfonyl)amide] ionic liquid (IL) solutions containing LiX (X=TFSA, PFSA, or HFSA) and C211 (4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane) were measured at various temperatures. As a result, it was found that the uncomplexed Li(I) species existing as [Li(X)(2)](-) in the present ILs exchange with the complexed Li(I) ([Li·C211](+)) and that the exchange reactions proceed through the bimolecular mechanism, [Li·C211](+) + [*Li(X)(2)](-)=[*Li·C211](+) + [Li(X)(2)](-). Kinetic parameters [k(s)/(kg m(-1) s(-1)) at 25 °C, ΔH(++)/(kJ mol(-1)), ΔS(++)/(J K(-1) mol(-1))] are as follows: 5.57×10(-2), 69.8 ± 0.4, and -34.9 ± 1.0 for the DEME-TFSA system; 5.77×10(-2), 70.6 ± 0.2, and -31.9 ± 0.6 for the EMI-TFSA system, 6.13×10(-2), 69.0 ± 0.3, and -36.7 ± 0.7 for the MPP-TFSA system; 1.35 × 10(-1), 65.2 ± 0.5, and -43.1 ± 1.4 for the DEME-PFSA system; 1.14×10(-1), 64.4 ± 0.3, and -47.1 ± 0.6 for the DEME-HFSA system. To compare these kinetic data with those in conventional nonaqueous solvents, the exchange reactions of Li(I) between [Li·C211](+) and solvated Li(I) in N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were also examined. These Li(I) exchange reactions were found to be independent of the concentrations of the solvated Li(I) and hence proposed to proceed through the dissociative mechanism. Kinetic parameters [k(s)/s(-1) at 25 °C, ΔH(++)/(kJ mol(-1)), ΔS(++)/(J K(-1) mol(-1))] are as follows: 1.10 × 10(-2), 68.9 ± 0.2, and -51.3 ± 0.4 for the DMF system; 1.13×10(-2), 76.3 ± 0.3, and -26.3 ± 0.8 for the DMSO system. The differences in reactivities between ILs and nonaqueous solvents were proposed to be attributed to those in the chemical forms of the uncomplexed Li(I) species, i.e., the negatively charged species ([Li(X)(2)](-)) in ILs, and the positively charged ones ([Li(solvent)(n)](+)) in nonaqueous solvents.

Molecular structure and electrochemical behavior of uranyl(VI) complex with pentadentate Schiff base ligand: prevention of uranyl(V) cation-cation interaction by fully chelating equatorial coordination sites.

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 1a and 1c does not show any coordination to U(VI)O(2)(saldien), but it is just present as a solvent in the crystal structures. The other isolated crystals consisted only of U(VI)O(2)(saldien) without incorporation of solvent molecules (1b, orthorhombic). A different conformation of the coordinated saldien(2-) in 1c from those in 1a and 1b was observed. The conformers exchange each other in a solution through a flipping motion of the phenyl rings. The pentagonal equatorial coordination of U(VI)O(2)(saldien) remains unchanged even in strongly Lewis-basic solvents, DMSO and N,N-dimethylformamide. Cyclic voltammetry of U(VI)O(2)(saldien) in DMSO showed a quasireversible redox reaction without any successive reactions. The electron stoichiometry determined by the UV-vis-NIR spectroelectrochemical technique is close to 1, indicating that the reduction product of U(VI)O(2)(saldien) is [U(V)O(2)(saldien)](-), which is stable in DMSO. The standard redox potential of [U(V)O(2)(saldien)](-)/U(VI)O(2)(saldien) in DMSO is -1.584 V vs Fc/Fc(+). This U(V) complex shows the characteristic absorption bands due to f-f transitions in its 5f(1) configuration and charge-transfer from the axial oxygen to U(5+).

µ-η:η-Peroxido-bis-[nitratodioxido-bis(pyrrolidin-2-one)uranium(VI)].

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) Šand 1.784 (4) Å, indicating that the oxidation state of U is exclusively 6+, i.e., UO(2) (2+). Furthermore, the O-O distance is 1.492 (8) Å, which is typical of peroxide, O(2) (2-). The U atom is eight-coordinated in a hexa-gonal-bipyramidal geometry. The coordinating atoms of the nitrate and pyrrolidine-2-one ligands and the µ-η(2):η(2)-O(2) (2-) unit are located in the equatorial plane and form an irregular hexa-gon. An inter-molecular hydrogen bond is found between N-H of the pyrrolidine-2-one ligand and the coordinating O of the same ligand in a neighboring complex. A second inter-molecular hydrogen bond is found between the N-H of the other pyrrolidine-2-one ligand and one of the uranyl oxido atoms.

trans-Tetra-kis(4-methyl-pyridine-κN)dioxidorhenium(V) hexa-fluorido-phosphate.

The title compound, [ReO(2)(C(6)H(7)N)(4)]PF(6), contains octa-hedral [ReO(2)(4-Mepy)(4)](+) cations (4-Mepy is 4-methyl-pyridine) and PF(6) (-) anions. Both the cation and the anion reside on special positions, the Re atom on a crystallographic center of inversion and the P atom on a C(2) axis parallel to the b axis. The Re(V) atom in the cation exhibits an octa-hedral coordination geometry with two O atoms in the apical positions and four N atoms of the 4-Mepy ligands in the equatorial plane. The Re=O and Re-N bond lengths fall in the typical ranges of trans-dioxidorhenium(V) complexes.

Bis(1,3-dimethyl-1,3-diazinan-2-one)dinitratodioxidouranium(VI).

The title compound, [U(NO(3))(2)O(2)(C(6)H(12)N(2)O)(2)], exhibits a hexa-gonal-bipyramidal geometry around the U(VI) ion, which is situated on an inversion centre and coordinated by two oxide ligands in the axial positions, and four O atoms from two bidentate NO(3) (-) and two O atoms from two 1,3-dimethyl-1,3-diazinan-2-one (DMPU) ligands in the equatorial plane. These ligands are located in trans positions. The -(CH(2))(3)- moiety in the DMPU ligand is disordered over two positions in a 0.786 (11):0.214 (11) ratio.