Iodine heptafluoride

Iodine heptafluoride, also known as iodine(VII) fluoride or even iodine fluoride, is the compound IF7. It has an unusual pentagonal bipyramidal structure, as predicted by VSEPR theory. The molecule can undergo a pseudorotational rearangment like the Berry mechanism but for a hepta coordinated system. It forms colorless 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 moldy, acrid odor.

Preparation
IF7 is prepared by passing F2 through liquid IF5 at 90 °C, then heating the vapors to 270 °C. Alternately, this compound can be prepared from fluorine and dried PdI2 or KI to minimize the formation of IOF5, an impurity arising by hydrolysis.

Safety considerations
IF7 is highly irritating to both the skin and the mucous membranes.