Crystallized powder of dihydroxide zirconium oxalate Zr(OH)2(C2O4) (ZrOx) was obtained by precipitation and the structure determined from powder X-ray data. The three-dimensional (3D) framework observed in (ZrOx) results from the interconnection of zirconium hydroxide chains 1∞[Zr(OH)2]2+ and zirconium oxalate chains 1∞[{Zr(C2O4)}2+]. Single crystals of (H11O5)2[Zr2(C2O4)5(H2O)4] (H2Zr2O5) were obtained by evaporation. The structure contains dimeric anions [Zr2(C2O4)5(H2O)4]2– connected through hydrogen bonds to hydroxonium ions (H11O5)+ to create a 3D supramolecular framework. The addition of ammonium or alkali nitrate led to the formation of single crystals of Na2[Zr(C2O4)3]·2H2O (Na2ZrOx3), M(H7O3)[Zr(C2O4)3]·H2O, M = K (KHZrOx3), M = NH4 (NH4HZrOx3), M(H5O2)0.5(H9O4)0.5[Zr(C2O4)3], M = Rb (RbHZrOx3), and M = Cs (CsHZrOx3). For the five compounds, the structure contains ribbons 1∞[{ZrOx3}2–] formed by entities Zr(C2O4)4 sharing two oxalates. In (Na2ZrOx3), the shared oxalates are in cis positions and the chain 1∞[Zr–Ox] is stepped with a Zr–Zr–Zr angle of 98.27(1)°. In the other compounds, the shared oxalates are in trans positions and the chains 1∞[Zr–Ox] are corrugated with Zr–Zr–Zr angles in the range 140.34(1)–141.07(1)°. In the compounds (MHZrOx3), the cohesion between the ribbons is ensured by the alkaline or ammonium cations and the hydroxonium ions (H7O3)+ for M = K, NH4, (H5O2)+, and (H9O4)+ for M = Rb and Cs. During the thermal decomposition of the alkaline-free zirconium oxalates (ZrOx), (H2Zr2Ox5), and (NH4HZrOx3), the formed amorphous zirconia is accompanied by carbon; the oxidation of carbon at about 540 °C to carbon dioxide is concomitant with the crystallization of the stabilized tetragonal zirconia.

A family of compounds with general chemical formula Ln2[(UO2)2V2O8]3·nH2O, where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Er, Yb, Y has been hydrothermally synthesized and structurally characterized. The structures of all these compounds can be described as the stacking of carnotite-type uranyl vanadate layers pillared by lanthanide–oxygen polyhedra. Except for La, they are isostructural, and the crystal structure determination of Nd2[(UO2)2V2O8]3·22H2O and Y2[(UO2)2V2O8]3·20H2O shows that the ud/du/du geometrical isomers of the uranyl vanadate layers are pillared by Nd(Oyl)2(H2O)7 and Y(Oyl)2(H2O)6 polyhedra, respectively, through interactions between the lanthanide ion and the oxygens Oyl of two vanadyl ions forming V═Oyl–Ln–Oyl═V entities. In the La compound, the ud/du geometrical isomers of the uranyl vanadate layers are pillared by La(Oyl)2(H2O)8, through interactions between the lanthanum ion and the oxygens Oyl of one vanadyl and one uranyl ion, forming U═Oyl–La–Oyl═V entities. Thermogravimetric and high-temperature X-ray diffraction studies show that the dehydration of the La compound is also singular; while the dehydration of other compounds involves a regular decrease in the interlayer space, for La it is realized through structural transitions. Upon partial dehydration, the La crystalline material undergoes a single-crystal to single-crystal transition between the 20- and 6-hydrates. Despite very large variation of the unit cell parameters and volume (ΔV = −27.8%!), the crystal remained of sufficient quality to allow the crystal structure determination of the hexahydrate. The total dehydration is reversible.

Depending on the nature of the 4f element, six different lanthanide oxalate families were hydrothermally synthesized in the presence of hydrazinium ions. Four of them correspond to the general formula N2H5[Ln(C2O4)2]·nH2O but have different structural formulas according to the number of coordinated water molecules or hydrazinium ions and the structural arrangement, N2H5[La(C2O4)2] (1); N2H5[{Ln2(N2H5)}(C2O4)4]·4H2O, Ln = Ce, Pr, Nd, and Sm (2); N2H5[{Ln(H2O)}(C2O4)2], Ln = Sm, Eu, Gd, Tb, Dy, and Ho (3); N2H5[Ln(C2O4)2]·nH2O, Ln = Yb, n = 3, and Lu, n = 2 (5). The two others do not contain hydrazinium ions. Compound 4, obtained only with Ln = Er and Tm, contains a neutral lanthanide oxalate arrangement, [{Ln(H2O)}2(C2O4)3]. Finally, in the experimental conditions, crystals of compound 6 were obtained only for Lu, [{Lu(H2O)2}2(C2O4)3]·2H2O. For Ln = La to Ho, with coordination number CN = 9, 3D oxalate-lanthanide anionic frameworks are formed for the largest Ln, from La to Sm, and 2D networks are obtained for the smaller, from Sm to Ho. For Ln = Er to Lu, with CN = 8, 3D oxalate-lanthanide frameworks are formed; a 2D network is obtained only for the smaller lanthanide, Lu. The structures of compounds 1, 3 for Ln = Tb (3-Tb) and Ho (3-Ho), 4 for Ln = Er (4-Er), 5 for Ln = Yb (5-Yb) and Lu (5-Lu), and (6) were determined from single-crystal X-ray diffraction data in space groups P21/c, Pbca, P21/n, Fddd and P1̅, respectively. Thermal behaviors were studied by thermogravimetric analysis and high temperature powder X-ray diffraction. Optical properties were measured by UV-vis and IR spectroscopy.

Double and triple thorium oxalates have been synthesized by successive evaporation of a solution of thorium nitrate, ammonium, or hydrazinium oxalate and hydrogen peroxide. Compounds M6Ca2Th2(C2O4)9 center dot nH(2)O (M = NH4+, N2H5+) (1) were first accidentally obtained due to the unexpected presence of calcium as impurities in the thorium nitrate used. Further evaporation led to the M2Th2(C2O4)(5)center dot nH(2)O (M = NH4+, N2H5+) (2) precipitation. After an additional evaporation of 2 weeks, compounds (2) transform into M4Th(C2O4)(4)center dot nH(2)O (M = NH4+, N2H5+) (3). In the three compounds, thorium is coordinated by five bidentate oxalate ions. In (1) Th(C2O4)(5) entities share an oxalate ion to form dimeric units further connected by Ca(C2O4)(5) (M = NH4+) or Ca(C2O4)(5)(H2O) (M = N2H5+) entities to build three-dimensional (3D) frameworks. Compounds (2) exhibit a 3D honeycomb thorium oxalate framework. Compounds (3) contain chains of oxalate-shared Th(C2O4)(5) entities, whereas, in solution, the compound (NH4)(2)Th-2(C2O4)(5)center dot 1.5H(2)O (2) reacts with oxalate ions and turns into compound (NH4)(4)Th(C2O4)(4)center dot 4H(2)O (3); in the solid state the chains of the compound (3) condense to form the 3D framework of the compound (2) and release solid ammonium oxalate.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Co-management of the actinides in an integrated closed fuel cycle by a pyrochemical process is studied at the laboratory scale in France in the CEA-ATALANTE facility. In this context the co-precipitation of U(III) and Pu(III) by wet argon sparging in LiCl-CaCl2 (30-70 mol%) molten salt at 705 degrees C is studied. Pu(III) is prepared in situ in the molten salt by carbochlorination of PuO2 and U(III) is then introduced as UCl3 after chlorine purge by argon to avoid any oxidation of uranium up to U(VI) by Cl-2. The oxide conversion yield through wet argon sparging is quantitative. However, the preferential oxidation of U(III) in comparison to Pu(III) is responsible for a successive conversion of the two actinides, giving a mixture of UO2 and PuO2 oxides. Surprisingly, the conversion of sole Pu(III) in the same conditions leads to a mixture of PuO2 and PuOCl, characteristic of a partial oxidation of Pu(III) to Pu(IV). This is in contrast with coconversion of U(III)-Pu(III) mixtures but in agreement with the conversion of Ce(III). (C) 2017 Elsevier B.V. All rights reserved.

Neodymium oxalate structure and morphology were modified by adding a phosphonate, NTMP, during the oxalic precipitation step. Spherical agglomerates of neodymium oxalate Nd-2(C2O4)(3)(H2O)6 center dot 12H(2)O composed of thin hexagonal rods were precipitated instead of decahydrated oxalate Nd-2(C2O4)(3)(H2O)6 center dot 4H(2)O with rod-like particles usually obtained in the absence of additive. Despite some differences in the complexation with NTMP and complexity from redox, the use of NTMP was successfully transposed to the plutonium system. Spherical agglomerates of plutonium (III) oxalate were so obtained, leading to spherical agglomerates of PuO2 after thermal treatment.

This study demonstrates the ability of ammonium uranyl peroxide nanoclusters U32R-NH4 to undergo exchange in between NH4(+) and trivalent (Nd(3+)) or tetravalent (Th(4+)) cations in the solid state. It paves the way for new promising routes for the synthesis of mixed uranyl peroxides. The exchange ability may also be considered for solution decontamination and synthesis of new mixed actinide-oxide precursors. Both of these applications could be used in the nuclear industry.

The flexibility of the ammonium ion environment is suitable for inducing the formation of several uranyl peroxides and peroxo-oxalates. For a given concentration of uranium and various oxalate/uranium ratios, by varying the pH with ammonium hydroxide, crystals of eight compounds have been isolated and characterized by X-ray diffraction, in addition to the studtite (UO2)(O-2)center dot 4H(2)O. All the compounds contain anionic uranyl polyhedra clusters with charge compensated by ammonium ions. Three are uranyl peroxides built from uranyl hexagonal bip-yramids [(UO2)(O-2)(3)](4-) or [(UO)(2)(O-2)(2)(OH)(2)](4-) (OH)2]4 - sharing peroxide or dihydroxyl equatorial edges to form cage clusters [(UO2)(28)(O-2)(42)](28-) (U-28) and [(UO2)(44)(O-2)(66)](44-) (U-44) in 7 and 3 respectively, or crown-shaped cluster [(UO2)(32)(O-2(OH)(2))(52)](40-) (U-32R) in 2. In these uranyl peroxides the pentagonal and hexagonal uranyl polyhedra rings are stabilized by ammonium ions. The other five compounds are uranyl peroxo-oxalates with various condensations of uranyl hexagonal bipyramids: (i) condensation of two [(UO2)(O-2)(C2O4)(2)] bipyramids by peroxide ion sharing to form the dimer [(UO2)(2)(O-2)(C2O4)(4)](6-) (U(2)Ox(4)) in 8, (ii) assembly of five [(UO2)(O-2)(2)(C2O4)] bipyramids linked by sharing peroxide to form the [(UO2)(5)(O-2)(5)(C2O4)(5)](10-) (U(5)Ox(5)) pentameric rings in 4 and 6, (iii) further condensation of 12 U(5)Ox(5) rings through bis-bidentate oxalates to create the [(UO2)(60)(O-2)(60)(C2O4)(30)](60-) (U(60)Ox(30)) nanosphere in 5, (iv) replacing an oxalate by two hydroxide ions in U(5)Ox(5) rings and sharing of the OH OH bridge between two pentamers to form the dimer of pentamers [(UO2)(10)(O-2)(10)(OH)(2)(C2O4)(8)](18-) (U(10)Ox(8)) in 9. In the last four compounds, the ammonium ions stabilize the pentameric cycles. The ammonium ion has different effects, particularly in the case of pentamers, and thus provides access to a large panel of cluster sizes.

Mixed actinide(III,IV) oxalates of the general formula M2.2UAn(C2O4)5·nH2O (An = Pu or Am and M = H3O(+) and N2H5(+)) have been quantitatively precipitated by oxalic precipitation in nitric acid medium (yield >99%). Thorough multiscale structural characterization using XRD and XAS measurements confirmed the existence of mixed actinide oxalate solid solutions. The XANES analysis confirmed that the oxidation states of the metallic cations, tetravalent for uranium and trivalent for plutonium and americium, are maintained during the precipitation step. EXAFS measurements show that the local environments around U(+IV), Pu(+III) and Am(+III) are comparable, and the actinides are surrounded by ten oxygen atoms from five bidentate oxalate anions. The mean metal-oxygen distances obtained by XAS measurements are in agreement with those calculated from XRD lattice parameters.

Two novel crystal growth syntheses dedicated to low solubility actinide-oxalate systems and adapted to glove box handling are described. These methods based on the use of precursors of either actinide metal or oxalic acid have been optimized on lanthanide systems (analogue of actinides(III)) and then assessed on real actinide systems. They allow the synthesis of several actinide oxalate single crystals, Am2(C2O4)3(H2O)3·xH2O, Th(C2O4)2·6H2O, M2+x[PuIV2−xPuIIIx(C2O4)5]·nH2O and M1−x[PuIII1−xPuIVx(C2O4)2·H2O]·nH2O. It is the first time that these well-known compounds are formed by crystal growth methods, thus enabling direct structural studies on transuranic element systems and acquisition of basic data beyond deductions from isomorphic (or not) lanthanide compounds. Characterizations by X-ray diffraction, UV–visible solid spectroscopy, demonstrate the potentialities of these two crystal growth methods to obtain oxalate compounds.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

AbstractIn view of a potential application of uranyl peroxides in mixed oxide (MOX) nuclear fuel fabrication from the PUREX process, it is demonstrated that an ammonium uranyl peroxide crown nanocluster (NH4)40 [(UO2)32(O2,(OH)2)52] ·nH2O (U32R‐NH4) undergoes an exchange reaction between NH4+ and Nd3+, Th4+, or Sr2+ cations.

The thermal decomposition of uranyl peroxide tetrahydrate, (UO2)O2(H2O)2.2H2O, was studied by combining high temperature powder X-ray diffraction, scanning electron microscopy, thermal analyses and spectroscopic techniques (Raman, IR and 1H NMR). In situ analyses reveal that intermediates and final uranium oxides obtained upon heating are different from that obtained after cooling at room temperature and that the uranyl precursor used to synthesize (UO2)O2(H2O)2·2H2O, sulfate or nitrate, has a strong influence on the peroxide thermal behavior and morphology. The decomposition of (UO2)O2(H2O)2·2H2O ex sulfate is pseudomorphic and leads to needle-like shaped particles of metastudtite, (UO2)O2(H2O)2, and UO3-x(OH)2x·zH2O, an amorphous phase found in air in the following of (UO2)O2(H2O)2 dehydration. (UO2)O2(H2O)2·2H2O and the compounds resulting from its thermal decomposition are very reactive towards hydrofluorination as long as their needle-like morphology is kept.

In the context of pyrochemical processes for nuclear fuel treatment, the precipitation of uranium (III) in molten salt LiCl-CaCl2 (30-70 mol%) at 705 degrees C is studied. First, this molten chloride is characterized with the determination of the water dissociation constant. With a value of 10(-4.0), the salt has oxoacid properties. Then, the uranium (III) precipitation using wet argon sparging is studied. The salt is prepared using UCl3 precursor. At the end of the precipitation, the salt is totally free of solubilized uranium. The main part is converted into UO2 powder but some uranium is lost during the process due to the volatility of uranium chloride. The main impurity of the resulting powder is calcium. The consequences of oxidative and reductive conditions on precipitation are studied. Finally, coprecipitation of uranium (III) and neodymium (III) is studied, showing a higher sensitivity of uranium (III) than neodymium (III) to precipitation. (C) 2016 Elsevier B.V. All rights reserved.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Americium oxalate single crystals, Am2(C2O4)3(H2O)6·4H2O, were prepared by in situ oxalic acid generation by slow hydrolysis of the diester. Their structure was determined by single-crystal X-ray diffraction and was solved by the direct methods and Fourier difference techniques. The structure (space group P21/c, a = 11.184(4) Å, b = 9.489(4) Å, c = 10.234(4) Å, β = 114.308(8)°, Z = 2) consists of layers formed by six-membered rings of actinide metals connected through oxalate ions. The americium atoms are nine-coordinated by six oxygen atoms from three bidentate oxalate ligands and three water molecules. The distances within the coordination sphere as well as infrared and Raman spectra of several isostructural lanthanide (Ce(III), Pr(III), Nd(III), Sm(III), Gd(III)) and actinide (Pu(III), Am(III)) oxalates were compared to evaluate the similarities and the differences between the two series.