•Complete overview of the wealth of actinide oxalate arrangements in the solid state.•Important role of actinide oxalates particularly in the nuclear industry.•Crystal growth methods adapted to ...actinide oxalates.•Recent progress crystal growth and structure determination of transuranic oxalates.•Ongoing research challenges with mixed actinide and/or mixed valence actinide oxalates.
Actinide oxalates are an important class of materials mainly for the nuclear industry. This review presents the crystal growth methods addressed to non-soluble actinide (III) and (IV) oxalates and to soluble actinyl oxalates. Actinide-oxalate discrete ions, one-dimensional coordination polymers and two- or three-dimensional frameworks are described for the different oxidation states of actinides in simple, double or triple actinide oxalates together with mixed actinide (IV)-lanthanide (III) or -actinide (III) and mixed ligands actinide oxalates. The main applications of actinide oxalates, particularly for radioactive waste management and nuclear fuel treatment and recycling are also reported.
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 N2H5Ln(C2O4)2·nH2O but have different structural formulas according to the number of coordinated water molecules or hydrazinium ions and the structural arrangement, N2H5La(C2O4)2 (1); N2H5{Ln 2(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); N2H5Ln(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.
We report and discuss here the unambiguous uranium valence state determination on the complex compound Ni(H2O)43U(OH,H2O)(UO2)8O12(OH)3 by using high-energy-resolution fluorescence detection–X-ray ...absorption near-edge structure spectroscopy (HERFD–XANES). The spectra at both U L3- and M4-edges confirm that all five nonequivalent U atoms are solely in the hexavalent form in this compound, as previously suggested by bond-valence-sum analysis and X-ray diffraction pattern refinement. Moreover, the presence of the preedge feature, due to the 2p3/2–5f quadrupole transition, has been observed in the U L3-edge HERFD–XANES spectrum, in agreement with theoretical and experimental observations of other uranium-based compounds. Recently, this feature has been proposed as a possible tool to determine the uranium oxidation state in a manner similar to that of 3d and 4d metals. Nevertheless, this feature is also very sensitive to the uranium local environment, as revealed by our theoretical calculations, and consequently could not be used to attribute without ambiguity the uranium valence state. In contrast, U M4-edge HERFD–XANES appears to be the most straightforward and reliable way to assess the uranium valence state in very complex materials such as Ni(H2O)43U(OH,H2O)(UO2)8O12(OH)3 or a mixture of compounds.
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)(O2)·4H2O. All the compounds contain anionic uranyl polyhedra clusters with charge compensated by ammonium ions. Three are uranyl peroxides built from uranyl hexagonal bipyramids (UO2)(O2)34– or (UO2)(O2)2(OH)24– sharing peroxide or dihydroxyl equatorial edges to form cage clusters (UO2)28(O2)4228– (U28) and (UO2)44(O2)6644– (U44) in 7 and 3 respectively, or crown-shaped cluster (UO2)32(O2(OH)2)5240– (U32R) 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)(O2)(C2O4)2 bipyramids by peroxide ion sharing to form the dimer (UO2)2(O2)(C2O4)46– (U2Ox4) in 8, (ii) assembly of five (UO2)(O2)2(C2O4) bipyramids linked by sharing peroxide to form the (UO2)5(O2)5(C2O4)510– (U5Ox5) pentameric rings in 4 and 6, (iii) further condensation of 12 U5Ox5 rings through bis-bidentate oxalates to create the (UO2)60(O2)60(C2O4)3060– (U60Ox30) nanosphere in 5, (iv) replacing an oxalate by two hydroxide ions in U5Ox5 rings and sharing of the OH–OH bridge between two pentamers to form the dimer of pentamers (UO2)10(O2)10(OH)2(C2O4)818– (U10Ox8) 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.
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)22+ and zirconium oxalate chains 1 ∞{Zr(C2O4)}2+. Single crystals of (H11O5)2Zr2(C2O4)5(H2O)4 (H2Zr2O5) were obtained by evaporation. The structure contains dimeric anions Zr2(C2O4)5(H2O)42- 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 Na2Zr(C2O4)3·2H2O (Na2ZrOx3), M(H7O3)Zr(C2O4)3·H2O, M = K (KHZrOx3), M = NH4 (NH4HZrOx3), M(H5O2)0.5(H9O4)0.5Zr(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.
In recent years, the hydrothermal conversion of actinide (IV) oxalates into nanometric actinide dioxides (AnO2) has begun to be investigated as an alternative to the widely implemented thermal ...decomposition method. We present here a comparison between the hydrothermal and the conventional thermal decomposition of Pu(IV) oxalate in terms of particle size, morphology and residual carbon content. A parametric study was carried out in order to define the temperature and time applied in the hydrothermal conversion of tetravalent Pu-oxalate into PuO2 and to optimize the reaction conditions.
A l'heure des restrictions énergétiques et du changement climatique, la nécessité de réduire -ou tout au moins de modifier- notre consommation d'énergies fossiles est devenue inéluctable. Ce constat ...a été confirmé par les participants de la COP 27 de Sharm el-Sheikh (Egypte, 6-18 novembre 2022), qui insistent sur la nécessité de diminuer les émissions de gaz à effet de serre afin d’atteindre la neutralité carbone en 2050. Pour aller en ce sens, de grands programmes sont avancés en France comm...
View of the intermolecular interactions N–H⋯O and O–H⋯O forming polymeric dihydrogendecavanadate(V)–decavanadate(V) chains running along the
1
1
¯
1
axis in NH
2(CH
2)
4
5V
10O
28H
2
0.5V
10O
28
...0.5.
A new polymeric compound, NH
2(CH
2)
4
5V
10O
28H
2
0.5V
10O
28
0.5, was obtained by
in situ synthesis of the organic cation from an aqueous solution of V
2O
5–HCl–NH
2(CH
2)
4NH
2. The crystal structure was solved by single-crystal X-ray diffraction. NH
2(CH
2)
4
5V
10O
28H
2
0.5V
10O
28
0.5 consists of dihydrogendecavanadate(V), H
2V
10O
28
4−, and decavanadate(V), V
10O
28
6−, units assembled in one-dimensional arrays by interanionic hydrogen bonds O–H⋯O and cation-anion N–H⋯O interactions. The latter involve pyrrolidinium cations, which were obtained in the compound instead of the starting butane-1,4-diamine. Pyrrolidinium cations further connect the polymeric chains into a three-dimensional network. The presence of the two types of units, H
n
V
10O
28
(6−
n
)− with
n
=
0 and
n
=
2, in one compound was not yet observed and is herein reported for the first time.
We report on the crystallite growth of nanometric NpO2 and UO2 powders. The AnO2 nanoparticles (An = U and Np) were synthesized by hydrothermal decomposition of the corresponding actinide(iv) ...oxalates. NpO2 powder was isothermally annealed between 950 °C and 1150 °C and UO2 between 650 °C and 1000 °C. The crystallite growth was then followed by high-temperature X-ray diffraction (HT-XRD). The activation energies for the growth of crystallites of UO2 and NpO2 were determined to be 264(26) kJ mol−1 and 442(32) kJ mol−1, respectively, with a growth exponent n = 4. The value of the exponent n and the low activation energy suggest that the crystalline growth is rate-controlled by the mobility of the pores, which migrate by atomic diffusion along the pore surfaces. We could thus estimate the cation self-diffusion coefficient along the surface in UO2, NpO2 and PuO2. While data for surface diffusion coefficients for NpO2 and PuO2 are lacking in the literature, the comparison with literature data for UO2 supports further the hypothesis of a surface diffusion controlled growth mechanism.
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