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.
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