The oxychloride, bromides, and other compounds were subsequently discovered; here we need only notice Moissan's preparation of the trifluoride and Thorpe's discovery of the pentafluoride, a compound of especial note, for it volatilizes unchanged, giving a vapour of normal density and so demonstrating the stability of a pentavalent phosphorus compound (the pentachloride and pentabromide dissociate into a molecule of the halogen element and phosphorus trichoride).
Columbium pentafluoride, CbF5, is obtained when the pentoxide is dissolved in hydrofluoric acid.
Tantalum pentafluoride, TaF5, for a long time only known in solution, may be obtained by passing fluorine over an alloy of tantalum and aluminium, and purifying by distillation in a vacuum.
Phosphorus pentafluoride, PF5, discovered by Thorpe (Proc. Roy.
Soc., 1877, 25, p. 122), may be obtained by burning the trifluoride in fluorine, from the pentachloride and arsenic trifluoride and from the trifluoride and bromine, the first formed fluorobromide, PF 3 Br 21 decomposing into the pentabromide and pentafluoride: 5PF 3 Br 2 =3PF 5 +2PBr 5.