An inorganic interhalogen species with the formula ClF5 that was tried as a rocket oxidizer in the 1960's. It is a gas at room temperature, but like perchloryl fluoride, it can be liquefied by pressure alone. Chlorine pentafluoride is one of the most powerful (in terms of specific impulse) non-cyrogenic liquid oxidizers in existence (except when coupled with carbon-containing fuels like kerosene).
Unfortunately, it corrodes tanks quite easily; even the almighty Teflon is eventually eaten away by it. However, some metals (like steel) form surface fluorides that inhibit corrosion by chlorine pentafluoride. Therefore, only those metals that form a fluoride layer can be used to store it.