Chlorine pentafluoride

Chlorine pentafluoride is an interhalogen compound with formula ClF5. This colourless gas is a strong oxidant that was once a candidate oxidizer for rockets. The molecule adopts a square pyramidal structure with C4v symmetry, as confirmed by its high-resolution 19F NMR spectrum. It was first synthesized in 1963.

Preparation
Some of the earliest research on the preparation was classified. It was first prepared by fluorination of chlorine trifluoride at high temperatures and high pressures:
 * ClF3 +  F2   →   ClF5
 * ClF +  2F2   →   ClF5
 * Cl2 +  5F2   →   2ClF5
 * CsClF4 +  F2   →   CsF  +  ClF5

NiF2 catalyzes this reaction.

Certain metal fluorides, MClF4 (i.e. KClF4, RbClF4, CsClF4), react with F2 to produce ClF5 and the corresponding alkali metal fluoride.

Reactions
In a highly exothermic reaction, ClF5 reacts with water to produce chloryl fluoride and hydrogen fluoride:
 * + 2 →  + 4

It is also a strong fluorinating agent. At room temperature it reacts readily with all elements (including otherwise "inert" elements like platinum and gold) except noble gases, nitrogen, oxygen and fluorine.

Rocket propellant
Chlorine pentafluoride was once considered for use as an oxidizer for rockets. As a propellant, it has a higher maximum specific impulse than ClF3, but with the same difficulties in handling. Due to the hazardous nature of chlorine pentafluoride, it has yet to be used in a large scale rocket propulsion system.