Chlorine pentafluoride

The gas chlorine pentafluoride (ClF₅) was first prepared by D. F. Smith in 1963 by the reaction of ClF₃ with F₂ under heat and pressure. It was previously an unknown compound. Ironically, it was predicted on the basis of the existence of XeF₄, which at the time was considered to be a novelty because it was believed that noble gases could not bind to other elements. ClF₅ has occasionally been tried as an oxidant, but the HCl and HF byproducts make this a bad idea.