Pentahalides phosphorus oxides

Phosphorus pentachloride, 79 40, 42-44 end use of chlorine, 6 135t sodium reactions with, 22 766 Phosphorus pentafluoride, 79 33 Phosphorus pentahalides, 79 31-33 Phosphorus pentoxide, 79 49, 69. See also Phosphorus(V) oxides as cellulose solvent, 77 272 in hydrogen fluoride manufacture, 74 11 vapor of, 79 49... 

Oxyfluorides are the most stable of the oxyhalides, and the stability decreases with increasing atomic weight of the halogen. Special methods are used in the preparation of oxyfluorides, while the other oxyhalides can be prepared by general reactions, such as the partial hydrolysis of the pentahalides, or the oxidation of the trihalides. The compounds fume in the air and readily undergo further hydrolysis giving hydrogen halides and oxyaeids of phosphorus. 

Phosphorus pentahalides PX5 (X = Cl and Br) are mild oxidants which were used already more than a century ago to oxidize platinum black to bridged dimers [Pt2(yU2-X)2X2(PX3)2] [235a]. Oxidative chlorination of Pt to PF complexes by PCI5 is classic, and compares favorably with use of CI2 which is common to carry out this reaction [235b]. 

Phosphorus pentahalides can react with a great variety of organic bases to form adducts, at least some of which are probably inner onium-ate compounds containing 6-coordinated P atoms. These bases include pyridine, tertiary amines, phenanthroline, symm dimethylurea, tertiary phosphine oxides and so forth (6.551, 6.552). Another onium-ate or zwitterionic phosphoride (6.553) can be made from the diphosphorane (6.540). 

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. 

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