Uranium pentafluoride is the inorganic compound with the chemical formula UF<sub>5</sub>. 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 ñ- and ò-UF<sub>5</sub>.
Uranium pentafluoride is an intermediate in the conversion of uranium tetrafluoride to volatile UF<sub>6</sub>:
It can be produced by reduction of the hexafluoride with carbon monoxide at elevated temperatures.
Other reducing agents have been examined.
The ñ 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 ò form, the uranium centers adopt a square antiprismatic structure. The ò polymorph gradually converts to ñ at 130 ðC.
Of theoretical interest, molecular UF<sub>5</sub> can be generated as a transient monomer by UV-photolysis of uranium hexafluoride. It is thought to adopt a square pyramidal geometry.