Uranium pentafluoride

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.

Uranium pentafluoride

β form
Identifiers
CAS Number	13775-07-0 Y
3D model (JSmol)	Interactive image
ChemSpider	75545 Y
ECHA InfoCard	100.033.991
EC Number	237-405-9
PubChem CID	83723
UNII	VG7WW26FTQ Y
CompTox Dashboard (EPA)	DTXSID7065625
InChI InChI=1S/5FH.U/h5*1H;/q;;;;; 5/p-5 N Key: JNVYCANIFQDNST-UHFFFAOYSA-I N InChI=1/5FH.U/h5*1H;/q;;;;;+2/p-5 Key: YKLDBRIIJYAXGS-AACRGIKGAA
SMILES [U+5].[F-].[F-].[F-].[F-].[F-]
Properties
Chemical formula	UF5
Molar mass	333.02 g/mol
Appearance	Pale yellow crystalline solid
Density	5.823 g/cm3 (alpha polymorph)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Synthesis and structure

Uranium pentafluoride is an intermediate in the conversion of uranium tetrafluoride to volatile UF₆:

2 UF₄ + F₂ → 2 UF₅

2 UF₅ + F₂ → 2 UF₆

It can be produced by reduction of the hexafluoride with carbon monoxide at elevated temperatures.^[1]

2 UF₆ + CO → 2 UF₅ + COF₂

Other reducing agents have been examined.^[2]

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.^[3] The structure is reminiscent of that for vanadium pentafluoride.

In the β form, the uranium centers adopt a square antiprismatic structure.^[4] The β polymorph gradually converts to α at 130 °C.^[3]

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.^[5]

Structure of molecular UF₅.