Bismuth pentahalide

Bismuth Halides. The bismuth trihalides are the best known. Bismuth does form a single pentahalide, BiF5, and subhalides that approximate the composition BiX, the best characterized of these being BiCl11(57. Vapors above solutions of a bismuth trihalide in molten bismuth contain the species BiX and/or (BiX)w, where X = Cl, Br, or I (9). At temperatures below 323°C, a black, diamagnetic, orthorhombic solid of the overall composition BiCl1 7 may be isolated from solutions of bismuth trichloride in molten bismuth (10). 

Both trihalides and pentahalides are known for arsenic, antimony, and bismuth. The 12 possible trihalides, all of... 

The decreasing stabUity of the +5 oxidation state is shown by the fact that all 16 EX3 compounds (E = P, As, Sb, Bi X = F, Cl, Br, I) are formed, but only phosphorus forms pentahalides with all four halogens. Arsenic and antimony form only the pentafluoride and pentachloride, whereas bismuth forms only the pentafluoride. Of the pentafluorides of the lower three pnicogens, only ASF5 is trigonal bipyrami-dal. SbFj and BiFj are polymers of EF octahedra held together by bridging fluorine atoms. 

Bismuth and antimony tend to be metallic, readily losing electrons to form cations. Although these elements have five valence electrons, so much energy is required to remove all five that no ionic compounds containing Bi or ions are known. Three pentahalides (Bip5, SbCls, and SbF5) are known, but these are molecular rather than ionic compounds. 

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