首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The title compound, {[U(C12H14O4)O2(H2O)]·H2O}n, is the first actinide complex featuring adamantanecarboxylate ligands. The metal ion possesses a pentagonal–bipyramidal UO7 coordination involving two axial oxide ligands [U—O = 1.732 (5) and 1.764 (5) Å] and five equatorial O atoms [U—O = 2.259 (5)–2.494 (4) Å] of aqua and carboxylate ligands. The latter display pseudo‐chelating and bridging coordination modes of the carboxylate groups that are responsible for the generation of the centrosymmetric discrete uranium–carboxylate [UO2(μ‐RCOO)2UO2] dimers [U...U = 5.5130 (5) Å] and their connection into one‐dimensional chains. Hydrogen bonding involving two coordinated and two solvent water molecules [O...O = 2.719 (7)–2.872 (7) Å] yields centrosymmetric (H2O)4 ensembles and provides noncovalent linkage between the coordination chains to generate a three‐dimensional network structure.  相似文献   

2.
Single crystals of complex uranium oxides, CaUO4, β-Ca3UO6, K4CaU3O12 and K4SrU3O12 were grown from carbonate melts. The crystal structures of the four uranates were determined by single crystal X-ray diffraction. CaUO4 crystallizes in the hexagonal space group R-3m, with lattice parameters a = 6.2570(7) Å and α = 36.04(2)°. The U6+ atom in CaUO4 is 8-coordinate and exhibits hexagonal bipyramidal geometry with six long and two short U–O bonds, typical of a uranyl species. β-Ca3UO6 forms in the monoclinic space group P21/n, with lattice parameters a = 5.728(1) Å, b = 5.956(1) Å, c = 8.298(2) Å, and β = 90.55(3)°, and adopts a distorted double perovskite structure. K4CaU3O12 and K4SrU3O12 crystallize in the cubic space group Im-3m with lattice parameters a = 8.483(1) Å and a = 8.582(1) Å, respectively. In all three perovskite-type oxides, the U(VI) cation is located in an octahedral coordination environment and exhibits typical uranyl geometry with four long and two short U–O bonds.  相似文献   

3.
On the basis of uranyl complexes reacting with a polypyrrolic ligand (H4L), we explored structures and reaction energies of a series of new binuclear uranium(VI) complexes using relativistic density functional theory. Full geometry optimizations on [(UO2)2(L)], in which two uranyl groups were initially placed into the pacman ligand cavity, led to two minimum‐energy structures. These complexes with cation–cation interactions (CCI) exhibit unusual coordination modes of uranyls: one is a T‐shaped ( T ) skeleton formed by two linear uranyls {Oexo?U2?Oendo→U1(?Oexo)2}, and another is a butterfly‐like ( B ) unit with one linear uranyl coordinating side‐by‐side to a second cis‐uranyl. The CCI in T was confirmed by the calculated longest distance and lowest stretching vibrational frequency of U2?Oendo among the four U?O bonds. Isomer B is more stable than T , for which experimental tetrameric analogues are known. The formation of B and T complexes from the mononuclear [(UO2)(H2L)(thf)] ( M ) was found to be endothermic. The further protonation and dehydration of B and T are thermodynamically favorable. As a possible product, we have found a trianglelike binuclear uranium(VI) complex having a O?U?O?U?O unit.  相似文献   

4.
Laser desorption ionization (LDI) mode of matrix-assisted laser desorptionionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of uranium(VI)leads to the formation of uranium oxides clusters, as with fast atom bombardment(FAB). Different uranium clusters than those with FAB were observed. Threedifferent families of formula (UO2)x Oy 2+, and two of formula (UO2)x Oy 2+ were found.  相似文献   

5.
The environmental behaviors of uranium closely depend on its interaction with natural minerals. Ferrihydrite widely distributed in nature is considered as one main natural media that is able to change the geochemical behaviors of various elements. However, the semiconductor properties of ferrihydrite and its impacts on the environmental fate of elements are sometimes ignored. The present study systematically clarified the photocatalysis of U(VI) on ferrihydrite under anaerobic and aerobic conditions, respectively. Ferrihydrite showed excellent photoelectric response. Under anaerobic conditions, U(VI) was converted to U(IV) by light-irradiated ferrihydrite, in the form of UO2+x (x < 0.25), where •O2 was the dominant reactive reductive species. At pH 5.0, ~50% of U(VI) was removed after light irradiation for 2 h, while 100% U(VI) was eliminated at pH 6.0. The presence of methanol accelerated the reduction of U(VI). Under aerobic conditions, the light illumination on ferrihydrite also led to an obvious but slower removal of U(VI). The removal of U(VI) increased from ~25% to 70% as the pH increased from 5.0 to 6.0. The generation of H2O2 under aerobic conditions led to the formation of UO4•xH2O precipitates on ferrihydrite. Therefore, it is proved that light irradiation on ferrihydrite significantly changed the species of U(VI) and promoted the removal of uranium both under anaerobic and aerobic conditions.  相似文献   

6.
The title complex, bis­(tetra­phenyl­phospho­nium) dioxobis(py­ridine-2,6-dicarbo­thio­ato-O,N,O′)­uranium(VI), (C24H20P)2[UO2(C7H3NO2S2)2], was prepared by reacting two equivalents of ­pyridine-2,6-bis­(mono­thio­carboxyl­ate) (pdtc) with uranyl nitrate. The geometry of the eight-coordinate U atom is hexagonal bipyramidal, with the uranyl O atoms in apical positions. This is the first reported complex in which this ligand binds a metal through the O and not the S atoms. Principal bond lengths include uranyl lengths of 1.774 (2) Å, U—O distances of 2.434 (2) and 2.447 (3) Å, and two U—N distances of 2.647 (3) Å. The anion lies on an inversion centre.  相似文献   

7.
This paper describes a new way of preparing nanometric powders of uranium oxide, to fit the needs of studies on UO2 oxidation, through the electrochemical reduction of U(VI) into U(IV). These powders can also be doped with radionuclides if necessary. The precipitation of oxides occurs in reducing and anoxic conditions. This original method makes it possible to synthesize nanometric UO2 powders with a calibrated size, as well as the Th- and La-doped UO2 powders with a predefined composition. The powder characterization by the X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron Microscopy shows the formation of spherical crystallites of UO2+x, (Th,U)O2+x and (La,U)O2+x phases. The composition can be defined by the initial Th/(Th+U) and La/(La+U) ratios in solution and the particle size can be controlled by varying the pH.  相似文献   

8.
FT–IR spectroscopy and single‐crystal X‐ray structure analysis were used to characterize the discrete neutral compound diaquadioxidobis(n‐valerato‐κ2O,O′)uranium(VI), [UO2(C4H9COO)2(H2O)2], (I), and the ionic compound potassium dioxidotris(n‐valerato‐κ2O,O′)uranium(VI), K[UO2(C4H9COO)3], (II). The UVI cation in neutral (I) is at a site of 2/m symmetry. Potassium salt (II) has two U centres and two K+ cations residing on twofold axes, while a third independent formula unit is on a general position. The ligands in both compounds were found to suffer severe disorder. The FT–IR spectroscopic results agree with the X‐ray data. The composition and structure of the ionic potassium uranyl valerate are similar to those of previously reported potassium uranyl complexes with acetate, propionate and butyrate ligands. Progressive lengthening of the alkyl groups in these otherwise similar compounds was found to have an impact on their structures, including on the number of independent U and K+ sites, on the coordination modes of some of the K+ centres and on the minimum distances between U atoms. The evolution of the KUO6 frameworks in the four homologous compounds is analysed in detail, revealing a new example of three‐dimensional topological isomerism in coordination compounds of UVI.  相似文献   

9.
In the title complex, [UCl(C2H6OS)7]Cl3, the uranium metal center is coordinated in a distorted bicapped trigonal prism geometry by seven O atoms from di­methyl sulfoxide ligands and by a terminal chloride ligand. Charge balance is maintained by three outer‐sphere chloride ions per uranium(IV) metal center. Principle bond lengths include U—O 2.391 (2)–2.315 (2) Å, U—Cl 2.7207 (9) Å, and average S—O 1.540 (5) Å.  相似文献   

10.
In the title complex, [UO2(dbm)2(PhSOPh)] or [UO2(C15H11O2)(C12H10OS)], where dbm is 1,3‐di­phenyl­propane‐1,3‐dionate, the U atom is surrounded by seven O atoms to give a distorted pentagonal bipyramidal geometry. The U—Ouranyl and U—Odbm distances (dbm is 1,3‐di­phenyl­propane‐1,3‐dionate) are in the ranges 1.760 (6)–1.776 (5) and 2.308 (4)–2.417 (4) Å, respectively, while the U—Osulfoxide distance is 2.427 (4) Å.  相似文献   

11.
The title compound was obtained by reacting UO2 powder in 2 M K2CO3 with hydrogen peroxide. The compound contains individual [U(CO3)2O2(O2)]4− ions, which are linked via an extended network of K atoms and hydrogen bonding. The U atom is coordinated to two trans‐axial O atoms and six O atoms in the equatorial plane, forming distorted hexagonal bipyramids. The carbonate ligands are bound to the U center in a bidentate manner, with U—O bond distances ranging from 2.438 (5) to 2.488 (5) Å. The peroxo group forms a three‐membered ring with the U atom, with U—O bond distances of 2.256 (6) and 2.240 (6) Å. The U=O bond distances of 1.806 (5) and 1.817 (5) Å, and an O—U—O angle of 175.3 (3)° are characteristic of the linear uranyl(VI) unit.  相似文献   

12.
There are very few examples in nature for U(VI) compounds with carbonate ligands other than the well known tricarbonates. Especially examples of U(VI) dicarbonato compounds are nearly completely missing. Even in aqueous solutions, the dicarbonato complex was found as a species of minorimportance only. On the basis of structural data on the ligands H2O and carbonate as well as the available data on U(VI) coordination compounds, steric requirements of equatorial coordination are studied for aqueous solution species. A pentagonally coordinated monocarbonato species [UO2CO3(H2O)3] is found as the most likely coordination. For the dicarbonato species, hexagonally coordinated [UO2(CO3)2(H2O)2] with D2h symmetry is found as most probable structure. Possible causes of the instability of U(VI) dicarbonato species are discussed.  相似文献   

13.
The U(VI) complex with cyanoacetic acid, [UO2(H2O)2(NCCH2COO)2] (I), was synthesized from an aqueous solution, and its X-ray diffraction analysis was carried out. The crystals are orthorhombic: space group Pca2 1, a = 25.9605(7) Å, b = 6.7634(2) Å, c = 6.3398(2) Å, V = 1113.15(6) Å3 at 100 K, and Z = 4. The coordination polyhedron of the uranium atom is a distorted pentagonal bipyramid. The cations UO 2 2+ are bound into infinite zigzag chains by the bridging carboxyl groups of one of the anions of cyanoacetic acid. The carboxyl oxygen atom of the second anion, which is not involved in coordination, and the nitrogen atoms of the cyano groups form hydrogen bonds with the coordination water molecules. The layer structure of the compound is formed through the hydrogen bonds. The absorption spectra in the visible and infrared ranges of the crystalline compound are measured and analyzed.  相似文献   

14.
Microwave-assisted dissolution of ceramic uranium dioxide in tri-n-butyl phosphate (TBP)–HNO3 complex was investigated. The research on dissolution of ceramic uranium dioxide in TBP–HNO3 inclusion complex under microwave heating showed the efficiency of the use of this method. Nitric acid present in the inclusion complex participates both dissolution of UO2, and oxidation of U(IV)–U(VI), the resulting UO2(NO3)2 extracted with tri-n-butyl phosphate. Dissolution rate depends on both temperature of microwave dissolution process, and concentration of nitric acid present in the inclusion complex. The most intensive dissolution process is when the concentration of nitric acid ≥2 mol/L and the temperature of 120 °C. From the experimental data obtained by two kinetic models activation energies were calculated. At the average activation energy of UO2 dissolution in TBP–HNO3 complex equal 70 kJ/mol, and reaction order is close to one, i.e. the reaction takes place in an area close to kinetic.  相似文献   

15.
Dissolution of UO2, U3O8, and solid solutions of actinides in UO2 in subacid aqueous solutions (pH 0.9–1.4) of Fe(III) nitrate was studied. Complete dissolution of the oxides is attained at a molar ratio of ferric nitrate to uranium of 1.6. During this process actinides pass into the solution in the form of U(VI), Np(V), Pu(III), and Am(III). In the solutions obtained U(VI) is stable both at room temperature and at elevated temperatures (60 °C), and at high U concentrations (up to 300 mg mL?1). Behavior of fission products corresponding to spent nuclear fuel of a WWER-1000 reactor in the process of dissolution the simulated spent nuclear fuel in ferric nitrate solutions was studied. Cs, Sr, Ba, Y, La, and Ce together with U pass quantitatively from the fuel into the solution, whereas Mo, Tc, and Ru remain in the resulting insoluble precipitate of basic Fe salt and do not pass into the solution. Nd, Zr, and Pd pass into the solution by approximately 50 %. The recovery of U or jointly U + Pu from the dissolution solution of the oxide nuclear fuel is performed by precipitation of their peroxides, which allows efficient separation of actinides from residues of fission products and iron.  相似文献   

16.
Acetylpyridine benzoylhydrazone and related ligands react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu4]2[UO2Cl4] to form air‐stable complexes. Reactions with 2, 6‐diacetylpyridinebis(benzoylhydrazone) (H2L1a) or 2, 6‐diacetylpyridinebis(salicylhydrazone) (H2L1b) give yellow products of the composition [UO2(L1)]. The neutral compounds contain doubly deprotonated ligands and possess a distorted pentagonal‐bipyramidal structure. The hydroxo groups of the salicylhydrazonato ligand do not contribute to the complexation of the metal. The equatorial coordination spheres of the complexes can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting deep‐red complexes have hexagonal‐bipyramidal coordination environments with the oxo ligands in axial positions. The sterical strains inside the hexagonal plane can be reduced when two tridentate benzoylhydrazonato ligands are used instead of the pentadentate 2, 6‐diacetylpyridine derivatives. Acetylpyridine benzoylhydrazone (HL2) and bis(2‐pyridyl)ketone benzoylhydrazone (HL3) deprotonate and form neutral, red [UO2(L)2] complexes. The equatorial coordination spheres of these complexes are puckered hexagons. X‐ray diffraction studies on [UO2(L1a)(pyridine)], [UO2(L1b)(DMSO)], [UO2(L2)2] and [UO2(L3)2] show relatively short U—O bonds to the benzoylic oxygen atoms between 2.328(6) and 2.389(8) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U—N bond lengths: 2.588(7)—2.701(6) Å ).  相似文献   

17.
During XPS analysis, the soft X‐ray‐induced reduction of metals such as Cr(VI) and Ce(IV) in oxides has been reported in the literature and some mechanisms have been proposed to explain this phenomenon. The reduction of U(VI) by the beam during X‐ray Photoelectron Spectroscopy has been already reported in the literature but only for U(VI) sorbed or precipitated onto solids with reducing properties (as micas or pyrites) for whose Fe(II) can also induce the reduction of U(VI), or onto TiO2 whose the photocatalytic properties are well known. The objective of this paper is to investigate the effects of X‐ray beam on U(VI) bulk compounds (UO3, UO2(OH)2, (UO2)2SiO4, UO2(CH3COO)2 and UO2C2O4). Successive U4f, U5f, C1s XPS spectra were recorded and compared as a function of the irradiation time. The XPS photoreduction of U(VI) into U(IV) is only observed for uranyl compounds containing organic matter (uranyl acetate and uranyl oxalate). Considering the evolution of the C1s signal during the X‐ray irradiation, a significant decrease of the C ? O component simultaneously to the U(VI) reduction is observed, which suggests a desorption of CO or other volatile organic products from the solid surface. All these results on U(VI) bulk compounds indicate the important role of organic carbon species in the photoreduction process and to explain these observations, a photoreduction mechanism has been suggested. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

18.

Crystal structure determinations on the uranyl ion complexes [H2N(CH3)2]2[UO2(bpdc)2], (1), (bpdc?=?2,2′-bipyridine-3,3′-dicarboxylate), [pyH]2[UO2(btfac)(NO3)2](NO3), (2), (btfac?=?1-phenyl-4,4,4-trifluorobutane-1,3-dionate), [H2dabco][UO2(nta)]2·3H2O, (3), (dabco?=?1,4-diazabicyclo[2.2.2]octane; nta?=?nitrilotriacetate) and [Ni(cyclam)UO2(edta)].2H2O, (4), (cyclam?=?1,4,8,11-tetrazacyclotetradecane; edta?=?ethylenediaminetetraacetate) have provided further examples of U(VI) in tetragonal-, pentagonal and hexagonal-bipyramidal coordination environments. Consideration of each structure within the context of those of known relatives has been used to assess the influence of factors in addition to repulsions within the primary coordination sphere on the equatorial coordination number of U(VI).

  相似文献   

19.

Polycarboxylic acid acts as hole scavenger and chelating agent, which is essential for the photocatalytic removal of multivalent metal ions. The photocatalytic uranium removal, role of chelating hole scavenger citric acid (CA), and removal mechanism were investigated in a TiO2 suspension system. The results show that chelating agent CA is an efficient hole scavenger. The maximum removal efficiency of U(VI) reaches up to 98.6%. The uranium-bearing precipitates contains Na[(UO2)(Cit)], UO2, or UO4·2H2O. The mechanisms for the photocatalytic removal of U(VI) and the role of CA are discussed. These results suggest that proper chelating hole scavengers can promote and regulate the photocatalytic removal of multivalent metal ions.

  相似文献   

20.
It was established that heating to 90 °C of nitrate solutions of U, Np and Pu in the presence of hydrazine hydrate results in the formation of hydrated dioxides of these elements. On ignition under inert or reducing conditions in the temperature range of 280–800 °C hydrated uranium dioxide transmogrify into crystalline UO2. On ignition in air atmosphere UO2·nH2O turns into UO3 at 440 °C and into U3O8 at 570–800 °C. It was shown that thermolysis of the solution containing a mixture of uranium, neptunium and plutonium nitrates at 90 °C in the presence of hydrazine hydrate allows one to prepare hydrated dioxides (U, Np, Pu)O2·nH2O which on heating to ~300 °C transmogrify into crystalline product of UO2, NpO2 and PuO2 solid solution. The technique of preparation of solid solutions of U and Pu dioxides is very promising as simple and effective method of production of MOX-fuel for.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号