Iodine heptafluoride is an interhalogen compound with the chemical formula IF<sub>7</sub>. It has an unusual pentagonal bipyramidal structure, with D<sub>5h</sub> symmetry, as predicted by VSEPR theory. The molecule can undergo a pseudorotational rearrangement called the Bartell mechanism, which is like the Berry mechanism but for a heptacoordinated system.
Below 4.5 ðC, IF<sub>7</sub> forms a snow-white powder of colorless crystals, melting at 5âÂÂ6 ðC. However, this melting is difficult to observe, as the liquid form is thermodynamically unstable at 760 mmHg: instead, the compound begins to sublime at 4.77 ðC. The dense vapor has a mouldy, acrid odour.
IF<sub>7</sub> is prepared by passing F<sub>2</sub> through liquid IF<sub>5</sub> at 90 ðC, then heating the vapours to 270 ðC. Alternatively, this compound can be prepared from fluorine and dried palladium or potassium iodide to minimize the formation of IOF<sub>5</sub>, an impurity arising by hydrolysis. Iodine heptafluoride is also produced as a by-product when dioxygenyl hexafluoroplatinate is used to prepare other platinum(V) compounds such as potassium hexafluoroplatinate(V), using potassium fluoride in iodine pentafluoride solution:
Iodine heptafluoride decomposes at 200 ðC to fluorine gas and iodine pentafluoride.
IF<sub>7</sub> is highly irritating to both the skin and the mucous membranes. It also is a strong oxidizer and can cause fire on contact with organic material.