U(<scp>vi</scp>) hydrazinates: structural and thermal decomposition features

Gerber, Evgeny; Krot, Anna; Andreadi, Karina; Averin, A. A.; Shiryaev, А. A.; Trigub, Alexander L.; Sobolev, Nikita; Nevolin, Iurii

doi:10.1039/d3nj01094e

Cited by 1 publication

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“…The reduction of the lattice parameter c and unit cell volume indicates that the uranyl sheets in polyuranates are not neutral and are strongly bonded by the electrostatic attraction with interlayer NH 4 + cations. In our previous investigation, we have explored the structural properties of uranium hydrazinate, a compound related to ammonium polyuranates and metaschoepite, and observed that interlayer hydrazine N 2 H 4 is present in the form of a neutral molecule rather than in an ionic form. Consequently, the lattice parameter c is significantly higher (14.75 Å) compared to uranium polyuranates, despite the fact that the N 2 H 4 molecule is larger (3.93 Å) than the ammonium cation NH 4 + (2.80–3.34 Å depending on the coordination number) …”

Section: Resultsmentioning

confidence: 99%

“…This phenomenon has been previously observed for ammonium polyuranates and illustrated its intramolecular redox instability. However, the thermal stability of ammonium polyuranates is significantly higher when compared to U(VI) hydrazinates since decomposition of x UO 3 · y N 2 H 4 · z H 2 O occurs in the temperature range of 100–150 °C, whereas for x UO 3 · y NH 3 · z H 2 O , exothermic oxidation of ammonia in the structure occurs in the range of 350–450 °C (Figure S5 and refs and ).…”

Section: Resultsmentioning

confidence: 99%

“…Characterization of Single-Phase Samples. The mass fractions of elements in single-phase samples are determined using the technique described previously: 35 mass fractions of N and H are determined by elemental analysis, while U�using TG−DTA since ammonium polyuranates decompose in air with the formation of stoichiometric U 3 O 8 at 800 °C. 5 The O mass fraction in samples is determined by subtraction, calculated as 100% − Σω(U,N,H).…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

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Ammonium Polyuranates: Old Dog, New Structural Tricks

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et al. 2024

Inorg. Chem.

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The crystal structure of ammonium polyuranates xUO 3 •yNH 3 •zH 2 O has been investigated. Powder X-ray diffraction (PXRD) has been employed to define single-phase samples within a series of synthesized compounds, which are further characterized by elemental analysis to ascertain the stoichiometry, revealing compositions of 3UO 3 •NH 3 •5H 2 O and 2UO 3 •NH 3 •3H 2 O. Analysis using extended X-ray absorption fine structure and vibrational spectroscopy has elucidated that both 3UO 3 •NH 3 •5H 2 O and 2UO 3 •NH 3 •3H 2 O possess a local structure similar to the metaschoepite�layered U(VI) oxohydroxide UO 3 •2H 2 O, but with H 2 O and NH 4 + groups in the interlayers. The structures of ammonium polyuranates are solved from PXRD data, revealing their relationship to the U(VI) oxohydroxide with the established composition of NH 4respectively. These structures maintain the arrangement of U−O polyhedra as pentagonal bipyramids. However, disparities in lattice parameters, space group, and layer topology from UO 3 •2H 2 O emphasize significant structural modifications resulting from the substitution of water by ammonium. Moreover, the anion topology of the NH 4 [(UO 2 ) 2 O 2 (OH)]•2H 2 O has no analogues among uranium oxohydroxide minerals. Notably, ammonium polyuranates, when compared, have minimal alterations in lattice parameters regardless of the presence of ammonia within the structure. The revealed results contribute valuable insights into the UO 3 −NH 3 − H 2 O system and hold potential applications in the field of nuclear power as ammonium polyuranates form during actinide precipitation in back-end of the nuclear fuel cycle and also serve as precursors in the fabrication of nuclear fuel.

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Section: Resultsmentioning

confidence: 99%