Uranium pentafluoride is the inorganic compound with the chemical formula UF5. It is a pale yellow paramagnetic solid. The compound has attracted interest because it is related to uranium hexafluoride, which is widely used to produce uranium fuel. It crystallizes in two polymorphs, called α- and β-UF5.
Synthesis and structure Uranium pentafluoride is an intermediate in the conversion of uranium tetrafluoride to volatile UF6: 2UF4 + F2 → 2UF5 2UF5 + F2 → 2UF6
It can be produced by reduction of the hexafluoride with carbon monoxide at elevated temperatures.Gordon W. Halstead, P. Gary Eller "Uranium(V) Fluorides and Alkoxides" Inorganic Syntheses 1982, volume 21, 162. 2UF6 + CO → 2UF5 + COF2 Other reducing agents have been examined.
It can also be produced by various molecular laser isotope separation methods.
The α form is a linear coordination polymer consisting of chains of octahedral uranium centers in which one of the five fluoride anion forms a bridge to the next uranium atom. The structure is reminiscent of that for vanadium pentafluoride.
In the β form, the uranium centers adopt a square antiprismatic structure. The β polymorph gradually converts to α at 130 °C.
Monomeric UF5 Of theoretical interest, molecular UF5 can be generated as a transient monomer by UV-photolysis of uranium hexafluoride. It is thought to adopt a square pyramidal geometry.
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