F,Sb Antimony pentafluoride

Starting with 1.00 g. (0.013 mole) of selenium and 5.00 g. (0.023 mole) of antimony pentafluoride, the procedure is at first identical with that for Se8(Sb2F11)2. However, when the room-temperature reaction is complete, the whole apparatus is placed in a 60° oven for 12 hours. A bright yellow solid and a yellow solution are obtained. As a safety precaution the oven is switched off and the apparatus is allowed to cool to room temperature before being removed. Three room-temperature extractions transfer all the Se4(Sb2F11)2 into flask B. After sulfur dioxide has been distilled, the product is removed from B and pumped to constant weight. The yield is quantitative. Anal. Calcd. for Se4Sb4F22 Se, 25.87 Sb, 39.89 F, 34.24. Found Se, 27.04 Sb, 38.54 F, 33.9. 

A mixture of 2.81 g. (22 mmoles) of tellurium and 10.25 g. (47 mmoles) of antimony pentafluoride in liquid sulfur dioxide is stirred for 3 days at — 23°. The solution develops a red color after about 2 hours of stirring at — 23°. The solution is filtered to leave a yellow residue, which is repeatedly washed with sulfur dioxide until the washings are colorless and all the red compound has been removed. In this particular reaction, since both red and yellow products are needed, flask B is not heat-sealed but is closed with a Nupro Teflon valve. After all the S02 has been removed under vacuum, flask B is heat-sealed at F. The yellow product is discussed below. The product obtained from flask B is a semicrystalline red material the yield is 6.0 g. (4.2 mmoles) 75% yield based on tellurium. Anal. Calcd. for Te4Sb4F22 Te, 35.97 Sb, 34.45 F, 29.60. Found Te, 35.88 Sb, 34.23 F, 32.21. 

Antimony pentafluoride (mp 280 K, bp 422 K) is prepared from Sbp3 and F2, or by reaction 14.85. In the solid state, Sbp5 is tetrameric (Figure 14.12a) and the presence of Sb—F—Sb bridges accounts for the very high viscosity of the liquid. Antimony pentachloride (mp 276 K, bp 352K)... 

Sixteen pentahalides could conceivably exist for combinations of P, As, Sb, and Bi with F, Cl, Br, and I. However, several of these possibilities are unknown, and others are of little importance. None of the elements forms a stable pentaiodide, but all of the pentafluorides are known. Phosphorus forms a pentachloride and a pentabromide, whereas antimony forms a pentachloride. As with the discussion of the trihalides, most of the discussion presented will center on the phosphorus compounds. 

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. 

---