Li3UHO3: A Uranium Hydride Oxide

Area of Science:

• Solid-state chemistry
• Inorganic chemistry
• Materials science

Background:

• Uranium oxides are well-studied, but uranium hydride oxides remain largely unexplored.
• Heteroanionic chemistry, involving multiple types of anions, offers pathways to novel materials.
• Understanding the structural and bonding properties of actinide compounds is crucial for fundamental science.

Purpose of the Study:

• To synthesize and characterize the first crystallographically defined uranium hydride oxide (oxyhydride).
• To investigate the crystal structure and bonding in the novel compound Li₃UHO₃.
• To explore the extension of heteroanionic hydride chemistry into the actinide series.

Main Methods:

• Salt-flux reaction of uranium dioxide (UO₂) with lithium hydride (LiH) at 973 K.
• Single-crystal X-ray diffraction for structural determination.
• ¹H/⁷Li Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and CHN elemental analysis for confirmation of hydride incorporation.

Main Results:

• Successful synthesis of Li₃UHO₃, a brown, air-sensitive solid.
• Determination of a novel rocksalt structure variant (space group *Pm*3*m*) with ordered oxide and hydride anions.
• Analysis revealed edge-sharing [LiH₂O₄] and [UO₆] octahedra with distinct Li-O and Li-H bond lengths, indicating weaker hydride coordination.

Conclusions:

• Li₃UHO₃ is the first crystallographically characterized uranium hydride oxide, establishing a new class of actinide materials.
• The compound exhibits a unique structure with ordered heteroanionic arrangement, extending known rocksalt variations.
• This work successfully incorporates hydride anions into actinide chemistry, paving the way for further exploration of heteroanionic hydride compounds.