Osmium metal

Figure 8.40 The k ySk) extended X-ray absorption fine structure (EXAFS) signal, Fourier transformed and then retransformed after application of the filter window indicated, in (a) osmium metal and (b) a 1% osmium catalyst supported on silica. (Reproduced, with permission, Ifom Winnick, FI. and Doniach, S. (Eds), Synchrotron Radiation Research, p. 413, Plenum, New York, 1980)...

Flowever, some associated materials might be perceived as toxic. For example, complexes of osmium find frequent use as electron mediators, because of their rich chemistry, stability, and redox activity. Osmium metal and most compounds are considered nontoxic, but the neat tetroxide of osmium is a strong oxidizer and is considered highly toxic in the U.S. and very toxic by the European Union. On the other hand, the aqueous solution, osmic acid, has been injected at 1% concentration in several European clinical trials, starting in the 1970s, for treatment of arthritis and hemophilia. - No toxic effects were observed. Thus, osmium toxicity might be a question not of in vivo chemistry, but of manufacture, where a concentrated form of the oxide might need to be handled. ... 

To separate osmium from ruthenium, the aqueous solution is acidified with nitric acid. While nitric acid oxidizes osmate ion to volatile osmium tetroxide, Os04, it converts ruthenium to a nitric oxide complex. Osmium tetroxide is removed from the solution by distillation in air and collected in an aqueous solution of caustic soda containing ethanol. Osmium tetroxide solution is heated with ammonium chloride, upon which osmium precipitates out as a complex chloride, 0s02(NH3)4Cl2. The precipitate is filtered, washed and decomposed by ignition with hydrogen to yield osmium metal. 

Osmium tetroxide is obtained as an intermediate during recovery of osmium metal from osmiridium or other noble metal minerals (See Osmium). In general, oxidation of an aqueous solution of an osmium salt or complex, such as sodium osmate with nitric acid, yields the volatile tetroxide which may be distilled out from the solution. In the laboratory, the compound can be prepared by oxidation of the osmium tetrachloride, OsCh, or other halide solutions with sodium hypochlorite followed by distdlation. 

Osmium tetroxide may also be produced by heating finely divided osmium metal in a stream of oxygen or air at 300 to 400°C. 

Heating osmium tetroxide with osmium metal forms osmium dioxide ... 

A number of generators were prepared using varying amounts of added "carrier osmium metal to determine the effect of the total amount of osmium metal on the yield and breakthrough. The... 

R.H. Grubbs, P. Schwab, and S.T. Nguyen, High metathesis activity ruthenium and osmium metal carbene complexes, US Patent 6 806 325, assigned to California Institute of Technology (Pasadena, CA), October 19, 2004. 

Osmium(II). The unsubstituted complex [Os(terpy)2]Cl2 was made in 1937 by fusion of the ligand with a mixture of K2[OsC1J and osmium metal, and is singularly unreactive towards either acids or alkalis.191 The green chloride gives a red solution. For its redox and spectroscopic properties see below. 

For Os(PMe2Ph)2 P(OR)2Ph Cl3 (R = Me, Et) see p. 572. Reaction of osmium metal with PC15 at 600 °C gives a brown, volatile solid OsCl3-PCl3, the magnetic susceptibility of which was measured from 77 to 373 K at the latter temperature ptS is 1.94 BM.438 Presumably this material has a polymeric structure so as to give it octahedral coordination. 

The so-called Os2OClg, made from osmium metal and a 15 1 chlorine-oxygen mixture at 700 °C,527 is thought from its IR spectrum to be OsOCL, (p. 584).525... 

The compound 0s03F2 (indistinguishable by X-ray methods from 0s02F3)533 is made by reaction of osmium metal with a 2 1 oxygen-fluorine mixture523 or from 0s04 and BrF3.524 There is much doubt about its structure, but the compound made at normal temperatures exists in at least three different crystalline forms and polymeric structures seem more likely.652... 

Preparation of Osmium Oxide Pentafluoride.—Osmium oxide pentafluoride was made in several ways, (a) Osmium metal was heated in a stream of oxygen and fluorine (1 2 v/v). The reaction was carried out in a quartz tube with the osmium in a nickel boat, and was initiated by the heat from a small flame. Once started, the reaction sustained itself. The product, which was caught in traps at —183°, was a mixture of an emerald green solid and a pale yellow, more volatile, solid. The difference in volatility of the components of the mixture permitted their separation by trap to trap sublimation under reduced pressure, from a trap held at —16° to receivers cooled with liquid nitrogen. The emerald green solid was retained in the —16° trap. The more volatile, yellow, component proved, from its infrared spectrum, to be osmium hexafluoride. The emerald green solid, m. p. 59-2°, established by infrared spectroscopy, to be free of OsFj, amounted to —50% of the product. 

It was assumed that OsO,F, would be colourless and diamagnetic and phjrsically similar to OsOF, and OsF,. The infrared spectra of osmium oxide pentafluoride samples taken from a variety of preparations were identical with one another. The entire product from one oxyfluorination of osmium metal was subjected to infrared examination. The bulk of the sample in a Monel trap, was isolated from the gas cell by a Hoke valve. After each vapour sample had been scanned it was discarded and a new sample of vapour admitted. This was repeated exhaustively. All the spectra were interpretable in terms of OsF OsOF OsO and traces of HF, CF, SiF and CO,. Two independent magnetic measurements on samples of OsOF one from an oxjrfluorination of the metal and the other from the fluorination of the dioxide gave magnetic susceptibility values equal within the usual experimental uncertainty. Furthermore the magnitude of the susceptibility was consistent with pure OsOF,. 

Osmium metal has few uses. It is sometimes added to platinum or iridium to make them harder. The osmium-platinum alloy is harder than pure platinum. Some alloys of osmium and platinum are used to make... 

Finely divided osmium metal is also used as a catalyst. A catalyst is a substance used to speed up a chemical reaction. The catalyst does not undergo any change itself during the reaction. The process for making ammonia from hydrogen and nitrogen sometimes uses osmium as a catalyst. 

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