U3F12(H2O), a Noncentrosymmetric Uranium(IV) Fluoride Prepared via a Convenient In Situ Route That Creates U4+ under Mild Hydrothermal Conditions

Uranium: The Nuclear Fuel Cycle and Beyond

This review summarizes the recent developments regarding the use of uranium as nuclear fuel, including recycling and health aspects, elucidated from a chemical point of view, i.e., emphasizing the rich uranium coordination chemistry, which has also raised interest in using uranium compounds in synthesis and catalysis. A number of novel uranium coordination features are addressed, such the emerging number of U(II) complexes and uranium nitride complexes as a promising class of materials for more efficient and safer nuclear fuels. The current discussion about uranium triple bonds is addressed by quantum chemical investigations using local vibrational mode force constants as quantitative bond strength descriptors based on vibrational spectroscopy. The local mode analysis of selected uranium nitrides, N≡U≡N, U≡N, N≡U=NH and N≡U=O, could confirm and quantify, for the first time, that these molecules exhibit a UN triple bond as hypothesized in the literature. We hope that this review will inspire the community interested in uranium chemistry and will serve as an incubator for fruitful collaborations between theory and experimentation in exploring the wealth of uranium chemistry.

Characterizing the solid hydrolysis product, UF4(H2O)2.5, generated from neat water reactions with UF4 at room temperature

Uranium tetrafluoride (UF₄) is an important intermediate in the production of UF₆ and uranium metal. Room temperature hydrolysis of UF₄ was investigated using a combination of Fluorine-19 nuclear magnetic resonance spectroscopy (¹⁹F NMR), Raman and infrared spectroscopy, powder X-ray diffraction, and microscopy measurements. UF₄(H₂O)_2.5 was identified as the primary solid hydrolysis product when anhydrous UF₄ was stirred in deionized water. Static NMR and ¹⁹F magic angle spinning NMR measurements revealed that a small amount of uranyl fluoride can also form when anhydrous UF₄ is left in water, although this species comprises less than 5% of the total sample with the remaining parts being UF₄(H₂O)_2.5. Since UF₄ is generally considered to be stable under ambient conditions, these findings mark the first time that a room temperature reaction between UF₄ and water has been detected and analyzed without interference from additional chemical reagents. The Raman characterization of UF₄(H₂O)_2.5 presented herein is the first on record. Since UF₄ is one of the most used intermediates during chemical conversion of uranium ore to uranium metal for nuclear fuel and weapons, the results presented herein are applicable to numerous nuclear science fields where solid state detection of uranium is of value, including nuclear nonproliferation, nuclear forensics, and environmental remediation.

Examination of Molten Salt Reactor Relevant Elements Using Hydrothermal Synthesis

The structural chemistry of elements relevant to the FLiBe molten salt reactor, Th, U, Np, and Zr, including Ce and Nd (as analogues for Pu and Am, respectively), have been examined using hydrothermal synthesis at 200 °C. These reactions serve to model the reaction of molten salts under hydrolysis conditions. The results show that U and Np formed LiAnF₅, while Ce formed Li₄CeF₈. The source of U also controlled the crystal quality, where UO₂ gave small crystals, while UO₃·2H₂O gave very large crystals. It is likely that Be incorporation was not observed because of the high solubility of [BeF₄]^2- in water. Zr formed a third product, Li₆BeF₄ZrF₈, which features isolated [BeF₄]^2- and [ZrF₈]^4- units bridged by Li⁺. Additionally, Li₂BeF₄ was regularly isolated. When little to no alkali metal was included in the reaction, M₃F₁₂(H₂O) was isolated for Np, U, and Ce.

From BiF3 to BiF3·H2O: diverse Bi(iii) coordination for structural transformation and birefringence regulation

BiF₃·H₂O with unprecedented BiF₉ building blocks was synthesized, which exhibits a near-isotropic Bi³⁺ coordination and inert lone pair activity.

Retention of a Paramagnetic Ground State at Low Temperatures in a Family of Structurally Related UIV Phosphates

A new uranium fluoride phosphate, UFPO₄, was synthesized via a mild hydrothermal route and characterized optically, thermally, and magnetically. Two thermal transformation products, U₂O(PO₄)₂ and U^IVU^VIO₂(PO₄)₂, were discovered to be structurally related, and were subsequently synthesized for bulk property measurements. All three materials failed to follow Curie-Weiss behavior at low temperatures, attributed to the nearly ubiquitous singlet ground state of U(IV), transitioning into a Curie-Weiss paramagnetic regime at high temperatures. Neutron diffraction experiments were performed on UFPO₄ and U^IVU^VIO₂(PO₄)₂ in order to characterize this unusual magnetic behavior.

Expanding pentafluorouranates: hydrothermal synthesis and characterization of β-NaUF5 and β-NaUF5·H2O

Two new sodium uranium(iv) pentafluorides eliminate the necessity of a copper catalyst in the synthesis of alkali metal uranium fluorides.

Application of a mild hydrothermal method to the synthesis of mixed transition-metal(ii)/uranium(iv) fluorides

The synthesis and properties of two families of mixed metal U(iv)/M(ii) fluorides via a mild hydrothermal method.

Synthetic strategies for new vanadium oxyfluorides containing novel building blocks: structures of V(iv) and V(v) containing Sr4V3O5F13, Pb7V4O8F18, Pb2VO2F5, and Pb2VOF6

Four novel vanadium oxyfluorides (VOFs) featuring new crystallographic building blocks were crystallizedviaa mild hydrothermal route.

Design and synthesis of a chiral uranium-based microporous metal organic framework with high SHG efficiency and sequestration potential for low-valent actinides

Microporous SCU-3 is synthesized with high SHG efficiency and Th⁴⁺ sequestration potential.