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Uranium pentafluoride is the
inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...
with the chemical formula UF5. It is a pale yellow
paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...
solid. The compound has attracted interest because it is related to
uranium hexafluoride Uranium hexafluoride, sometimes called hex, is the inorganic compound with the formula . Uranium hexafluoride is a volatile, white solid that is used in enriching uranium for nuclear reactors and nuclear weapons. Preparation Uranium dioxide is co ...
, 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 Uranium tetrafluoride is the inorganic compound with the formula UF4. It is a green solid with an insignificant vapor pressure and low solubility in water. Uranium in its tetravalent ( uranous) state is important in various technological process ...
to volatile UF6: :2UF4 + F2 → 2UF5 :2UF5 + F2 → 2UF6 It can be produced by reduction of the hexafluoride with
carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
at elevated temperatures. : 2UF6 + CO → 2UF5 + COF2 Other reducing agents have been examined. The α form is a linear
coordination polymer Coordination may refer to: * Coordination (linguistics), a compound grammatical construction * Coordination complex, consisting of a central atom or ion and a surrounding array of bound molecules or ions ** A chemical reaction to form a coordinat ...
consisting of chains of octahedral uranium centers in which one of the five fluoride anion forms a
bridge A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...
to the next uranium atom. The structure is reminiscent of that for vanadium pentafluoride. In the β form, the uranium centers adopt a
square antiprism In geometry, the square antiprism is the second in an infinite family of antiprisms formed by an even number, even-numbered sequence of triangle sides closed by two polygon caps. It is also known as an ''anticube''. If all its faces are regular ...
atic
structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...
. The β polymorph gradually converts to α at 130 °C.


Monomeric UF5

Of theoretical interest, molecular UF5 can be generated as a transient
monomer A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization. Classification Chemis ...
by UV-
photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by absorption of light or photons. It is defined as the interaction of one or more photons wi ...
of
uranium hexafluoride Uranium hexafluoride, sometimes called hex, is the inorganic compound with the formula . Uranium hexafluoride is a volatile, white solid that is used in enriching uranium for nuclear reactors and nuclear weapons. Preparation Uranium dioxide is co ...
. It is thought to adopt a square pyramidal geometry.


References

{{Actinide halides Uranium(V) compounds Nuclear materials Fluorides Actinide halides Inorganic polymers Coordination polymers