Separation of uranium and thorium using tris(2-ethylhexyl) phosphate as extractant

The distribution behavior of uranium and thorium has been investigated in a biphasic system of different aqueous nitric acid concentrations and a solution of tris(2-ethylhexyl) phosphate (TEHP) inn-dodecane at 25°C. The effect of different uranium and thorium concentrations in the aqueous phase on the extraction of these metal ions is evaluated. These results indicate that TEHP is a better choice than tri-n-butyl phosphate (TBP) for the separation of²³³U from the irradiated thorium matrix.     

Lanthanide(III)/actinide(III) differentiation in coordination of azine molecules to tris(cyclopentadienyl) complexes of cerium and uranium

Reaction of azine molecules L with the trivalent metallocenes [M(C5H4R)3](M = Ce, U; R = But, SiMe3) in toluene gave the Lewis base adducts [M(C5H4R)3(L)](L = pyridine, 3-picoline, 3,5-lutidine, 3-chloropyridine, pyridazine, pyrimidine, pyrazine, 3,5-dimethylpyrazine and s-triazine), except in the cases of M = U and L = 3-chloropyridine, pyridazine, pyrazine and s-triazine where oxidation of U(III) was found to occur. In the pairs of analogous compounds of Ce(III) and U(III), i.e.[M(C5H4But)3(L)](L = pyridine, picoline) and [M(C5H4SiMe3)3(L)](L = pyridine, lutidine, pyrimidine and dimethylpyrazine), the M-N and average M-C distances are longer for M = Ce than for M = U; however, within a series of azine adducts of the same metallocene, no significant variation is noted in the M-N and average M-C distances. The equilibria between [M(C5H4R)3], L and [M(C5H4R)3(L)] were studied by 1H NMR spectroscopy. The stability constants of the uranium complexes, KUL, are greater than those of the cerium counterparts, KCeL. The values of KML are much greater for R = SiMe3 than for R = But and a linear correlation is found between the logarithms of KML and the hydrogen-bond basicity pKHB scale of the azines. Thermodynamic parameters indicate that the enthalpy-entropy compensation effect holds for these complexation reactions. Competition reactions of [Ce(C5H4R)3] and [U(C5H4R)3] with L show that the selectivity of L in favour of U(III) increases with the [small pi] donor character of the metallocene and is proportional to the pi accepting ability of the azine molecule, measured by its reduction potential.     

多(三甲硅基)取代环戊二烯基二羰基钼环卡宾配合物的合成和结构

三(三甲基硅基)环戊二烯在一缩二乙二醇二甲醚或四氢呋喃中经n-BuLi处理后, 随之与Mo(CO)6加热, 生成相应的环戊二烯基羰基钼负离子锂盐[η^5-{(Me3Si)3C5H5-n}Mo^-(CO)3]Li^+(n=2, 3)(1), 同时观察到有脱硅基现象发生。1与X(CH2)3X在一缩二乙二醇二甲醚中反应, 无论X=I或Br, 均生成标题化合物[X=I: n=3(2), n=2(3); X=Br: n=3(4), n=2(5)]。1与X(CH2)3X的反应如在THF中进行, 则只有当X=I时才能生成环卡宾钼配合物。以元素分析, IR, 1H NMR和13C NMR表征了2-5的结构, 并用X射线衍射测定了4的晶体结构。晶体属单斜晶系,空间群为P21/n, 晶胞参数a=1.2611(3), b=1.2434(2),c=1.7095(6)nm, β=91.07(2)°, V=2.680(2)nm^3,Dc=1.563g.cm^-^3, Z=4, 最终偏差因子R=0.062, Rw=0.054.     

Synthesis and reactivity of bis(imido) uranium(VI) cyclopentadienyl complexes

The bis(imido) uranium(VI)-C(5)H(5) and -C(5)Me(5) complexes (C(5)H(5))(2)U(N(t)Bu)(2), (C(5)Me(5))(2)U(N(t)Bu)(2), (C(5)H(5))U(N(t)Bu)(2)(I)(dmpe), and (C(5)H(5))(2)U(N(t)Bu)(2)(dmpe) can be synthesized from reactions between U(N(t)Bu)(2)(I)(2)(L)(x) (L=THF, x=2; L=dmpe, x=1) and Na(C(5)R(5)) (R=H, Me); these complexes represent the first structurally characterized C(5)H(5)-compounds of uranium(VI) and they further highlight the differences between UO(2)(2+) and the bis(imido) fragment.     

Structural studies of two-coordinate complexes of tris(2-methoxylphenyl)phosphine and tris(4-methoxyphenyl)phosphine with gold(I) halides

A series of five gold(I) halide complexes with the two isomeric methoxy-substituted triarylphosphines, tris(2-methoxyphenyl)phosphine [P(oanis)₃], [AuP(oanis)₃X] [for X = Cl, (1); X = Br, (2) and X = I, (3)] and tris(4-methoxyphenyl)phosphine [P(panis)₃], [AuP(panis)₃X] [for X = Br (4) and X = I (5)] have been synthesized and characterized by single crystal X-ray diffraction and solution ³¹P{¹H} NMR spectroscopy. The structure determinations confirm the expected presence of linear two-coordination about the gold centres in all five complexes with bond distance and angle data typical of this type of compound [Au–P, 2.239(2)–2.259(3) Å; Au–Cl, 2.294(2) Å; Au–Br, 2.385(2)–2.402(2) Å; Au–I, 2.546(1)–2.554(1) Å; P–Au–X; 175.3(1)–180°]. All analogues except the iodo complex 5 crystallize with one complex molecule in the crystallographic asymmetric unit. The bromo and iodo complexes 2 and 3 constitute a trigonal isomorphous set while the bromo complex 4 is also isomorphous with the previously determined chloro complex [AuP(panis)₃Cl]. The 2-methoxy analogues are stabilized by significant methoxy-O?Au interactions.     

A theoretical study of the 3d-M(smif)2 complexes: structure, magnetism, and oxidation states

We carry out a theoretical investigation of the recently reported M(smif)(2) series1,2 and find a number of interesting phenomena. These include complex potential energy surfaces with near-degenerate stationary points, low-lying states, non-trivial electron configurations, as well as non-innocent ligand behavior. The M(smif)(2) exhibit a delicate balance between geometry and electronic structure, which has implications not only for their reactivity but also for controlling their properties through ligand design. We address methodological issues and show how conceptual quantities such as oxidation states and electronic configurations can be extracted through a simple analysis of the electron and spin densities-without a complicated examination of the underlying orbitals.     

Homoleptic tris(dithiolene) and tetrakis(dithiolene) complexes of uranium(IV)

Reaction of UCl4 with 3 or 4 mol equiv of Na2dddt (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) in THF afforded the first example of a tetrakis(dithiolene) metal compound, [Na4(THF)8U(dddt)4](infinity) (1). The red crystals of 1 are composed of infinite zigzag chains in which Na2(micro-THF)3 fragments ensure the linking of Na2(THF)5U(dddt)4 moieties; the uranium atom is in a dodecahedral environment of eight sulfur atoms. Treatment of UCl4 with 3 mol equiv of Na2dddt in pyridine gave a mixture of tris- and tetrakis(dithiolene) compounds. After addition of 18c6 (18-crown-6), only the tris(dithiolene) complex was obtained and crystallized as orange crystals of [Na(18c6)(py)2]2[U(dddt)3].2py (2.2py) in which the isolated [U(dddt)3]2- anion adopts a slightly distorted trigonal prismatic configuration. A few red crystals of the unsolvated complex 2 and the trinuclear anionic compound [Na(18c6)(py)2]3[Na{U(dddt)3}2] (3) were also obtained along with orange crystals of 2.2py. All the tris(dithiolene) compounds exhibit large folding of the dddt ligand and significant interaction between the C=C double bond and the metal center.     

Extraction studies of uranium(VI) and thorium(IV) with tributylphosphine oxide

Clay minerals occur widely in nature and play a very important role in agriculture, mineral recovery and chemical manufacturing. Among the many properties which affect clay behaviour, water binding and ion exchanging appear to be the most important. The study of the cation exchange capacity of soils is of great theoretical and practical importance since the CEC determines in many ways the behavior of nutrients, chemical amendments, and many toxic compounds entering the sols. Sorption interactions with montmorillonite and other clay minerals in soils are potantially important mechanisms for attenuating the mobility of heavy metal cations through the subsurface environment. In this work the cation exchange capacity (CEC) of montmorillonite from west Anatolia, and sorptions with montmorillonite for attenuating the mobility of uranium were studied. The CEC value was found to be 77 meq/100 g montmorillonite. The relative importance of test parameters e.g., contact time, particle size, pH and U(+6) aqueous speciation was determined. The results show that sorption on montmorillonite is a funtion of pH depending strongly on the aqueous U(+6) species. It reaches a maximum at near neutral pH(pH}7). At low and at high pH solutions the sorption values of uranium are poor. These sorption values were attributed to the formation of aqueous U(+6) carbonate complexes in alkaline conditions and the ionexchange process between UO₂ ⁺² species and interlayer cations on montmorillonite in acidic solutions.     

Separation studies of uranium and thorium using tetra(2-ethylhexyl) diglycolamide (TEHDGA) as an extractant

The extraction behavior of uranium, thorium and nitric acid has been investigated for the TEHDGA/isodecyl alcohol/n-dodecane solvent system. Conditional acid uptake constant (K _H) of TEHDGA/n-dodecane and the ratio of TEHDGA to nitric acid were obtained as 1.72 and 1:0.96, respectively. The extracted species of uranium and thorium in the organic phase were found to be UO₂(NO₃)₂·2TEHDGA and Th(NO₃)₄·2TEHDGA. A workable separation factor (D _Th/D _U) of the order of 300 was observed between thorium and uranium in the nitric acid range of 0.5M to 1.5M. Similar separation factor was also achieved at higher acidity when thorium was present in large concentration compared to uranium. These results indicate that TEHDGA solvent system could be a potential candidate for separation of thorium from uranium.     

Electrochemical studies of bimetallic rhenium(III) complexes possessing two accessible mixed-valence states

Summary Bimetallic complexes of the general formula [Cl₃(PPh₃)₂Re^III(NCArCN)Re^III(PPh₃)₂Cl₃] (where NCArCN represents an aromatic dinitrile) have been prepared and their solution phase electrochemistry examined. Each of these complexes undergoes two one-electron metal-centred oxidations. The potential difference between these oxidations gives a measure of the stability of the Re^III/Re^IV mixed-valence state toward disproportionation, and ranges from <0.050 V in the most weakly coupled system (4,4-biphenyldicarbonitrile bridge) to ca. 0.200 V for the most strongly interacting metal centres (9,10-dicyanoanthracene bridge). Likewise, all of the complexes show two one-electron transfers in either simultaneous or sequential fashion depending on the nature of the bridge.     

Optical, Electrochemical, and Catalytic Properties of the Unsaturated Host Pd3(dppm)3(CO)2+ and Pd4(dppm)4(H)2+ 2 Clusters: An Overview

This paper presents an overview of the optical, photophysical, and photochemical properties including UV-visible and luminescence spectra in solution at 298 and 77 K, along with electrochemical, and catalytic behavior under reduction conditions (for both thermally and electrochemically assisted systems) of the tri- and tetranuclear Pd₃(dppm)₃(CO)²⁺ and Pd₄(dppm)₄(H)²⁺ ₂ clusters (dppm=bis(diphenylphosphino)methane). This review is also complemented with relevant information about their syntheses, molecular and electronic structures supported from computer modeling, EHMO and DFT calculations, and their host-guest behavior with anions and neutral molecules, in relation with their observed reactivity.     

Structural studies of diiron complexes with monophosphine ligands tris(4-chlorophenyl)phosphine or diphenyl-2-pyridylphosphine

Four diiron dithiolate complexes with monophosphine ligands have been prepared and structurally characterized. Reactions of (μ-SCH₂CH₂S-μ)Fe₂(CO)₆ or [μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₆ with tris(4-chlorophenyl)phosphine or diphenyl-2-pyridylphosphine in the presence of Me₃NO·2H₂O afforded diiron pentacarbonyl complexes with monophosphine ligands (μ-SCH₂CH₂S-μ)Fe₂(CO)₅[P(4-C₆H₄Cl)₃] (1), (μ-SCH₂CH₂S-μ)Fe₂(CO)₅[Ph₂P(2-C₅H₄N)] (2), [μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₅[P(4-C₆H₄Cl)₃] (3), and [μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₅[Ph₂P(2-C₅H₄N)] (4) in good yields. Complexes 1–4 were characterized by elemental analysis, ¹H NMR, ³¹P{¹H} NMR and ¹³C{¹H} NMR spectroscopy. Furthermore, the molecular structures of 1–4 were confirmed by X-ray crystallography.