Iodine heptafluoride, also known as iodine(VII) fluoride or iodine fluoride, is an
interhalogen compound with the chemical formula
I F7. It has an unusual
pentagonal bipyramidal structure, as predicted by
VSEPR theory
Valence shell electron pair repulsion (VSEPR) theory ( , ), is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm the ...
. The molecule can undergo a
pseudorotation
In chemistry, a pseudorotation is a set of intramolecular movements of attached groups (i.e., ligands) on a highly symmetric molecule, leading to a molecule indistinguishable from the initial one. The International Union of Pure and Applied Chem ...
al rearrangement called the
Bartell mechanism The Bartell mechanism is a pseudorotational mechanism similar to the Berry mechanism. It occurs only in molecules with a pentagonal bipyramidal molecular geometry, such as IF7. This mechanism was first predicted by H. B. Bartell. The mechanism exc ...
, which is like the
Berry mechanism
The Berry mechanism, or Berry pseudorotation mechanism, is a type of vibration causing molecules of certain geometries to isomerize by exchanging the two axial ligands (see Figure at right) for two of the equatorial ones. It is the most widely ac ...
but for a heptacoordinated system.
It forms colourless crystals, which melt at 4.5 °C: the liquid range is extremely narrow, with the boiling point at 4.77 °C. The dense vapor has a mouldy, acrid odour. The molecule has
D5h symmetry.
Preparation
IF
7 is prepared by passing
F2 through liquid
IF5 at 90 °C, then heating the vapours to 270 °C. Alternatively, this compound can be prepared from fluorine and dried
palladium or
potassium iodide
Potassium iodide is a chemical compound, medication, and dietary supplement. It is a medication used for treating hyperthyroidism, in radiation emergencies, and for protecting the thyroid gland when certain types of radiopharmaceuticals are u ...
to minimize the formation of IOF
5, an impurity arising by hydrolysis. Iodine heptafluoride is also produced as a by-product when
dioxygenyl hexafluoroplatinate
Dioxygenyl hexafluoroplatinate is a compound with formula O2PtF6. It is a hexafluoroplatinate of the unusual dioxygenyl cation, O2+, and is the first known compound containing this cation. It can be produced by the reaction of dioxygen with platin ...
is used to prepare other platinum(V) compounds such as
potassium hexafluoroplatinate(V), using
potassium fluoride
Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali halide and occurs naturally as the rare ...
in iodine pentafluoride solution:
:2 O
2PtF
6 + 2 KF + IF
5 → 2 KPtF
6 + 2 O
2 + IF
7
Reactions
Iodine heptafluoride decomposes at 200 °C to fluorine gas and iodine pentafluoride.
Safety considerations
IF
7 is highly irritating to both the skin and the
mucous membranes
A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...
. It also is a strong oxidizer and can cause fire on contact with organic material.
References
External links
WebBook page for IF7*
ttp://www.webelements.com/webelements/compounds/text/I/F7I1-16921963.html web elements listing
{{fluorine compounds
Fluorides
Iodine compounds
Interhalogen compounds
Oxidizing agents
Hypervalent molecules