Osmium infrared spectra

The pentanuclear carbido species Ms(CO)lsC (M = Fe, Ru, Os) have been prepared. The iron compound has been known for some considerable time (209), but the ruthenium and osmium complexes were prepared recently by pyrolysis reactions (210). The ruthenium adduct was only isolated in low yield (—1%), while the osmium complex was obtained in higher yield (—40%). The infrared spectrum and mass spectral breakdown pattern indicate a common structure to these compounds. The molecular structure of the iron complex is shown in Fig. 46. 

The structure of FeRu3(CO)i3H2 is shown in Fig. 10 and the infrared spectrum of the iron/osmium analogue suggests it is /so-structural. 

This compound is the only one known for these elements in this oxidation state it is obtained as a highly-colored solid by the high-temperature reaction between fluorine and the metal. The solid is isostructural with the hexafluorides of osmium and iridium, and the Pt-F distance has been estimated at 1 83 A by extrapolation along the series W-Os-Ir 255). The infrared spectrum has been assigned in Oh symmetry 256) there are no signs of any distortion, as found for example in osmium hexafluoride. 

In their original paper (2) on the structure of Fe5C(CO)l5, Dahl and co-workers assigned two bands in the infrared spectrum of hydrocarbon solutions of the cluster, at 790 and 770 cm-1, to vFeC modes. This assignment has been confirmed by a recent study of the infrared spectra of the series M5C(CO)15, (M = Fe, Ru, Os) (78). The room temperature spectra of the compounds (Table II) in the solid state are quite similar to each other, comprising three bands assigned as the a, and e modes (split in the solid state) expected for the C4 symmetry of the isostructural clusters. At low temperature the ruthenium and osmium clusters exhibit five absorptions associated with M-C stretches, whereas the iron cluster retains its room temperature spectrum. This is ascribed to the presence of two types of cluster molecule in the crystal lattices of the ruthenium and osmium clusters which are isostructural with, but not isomorphous with, the iron analog in which all the molecules are identical. 

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. 

Carbonylchlorohydridotris(triphenylphosphine)osmium(II) forms white microcrystals which melt with decomposition in air at 179-183° and at 289-290° in a capillary sealed under nitrogen. The infrared spectrum shows bands at 2099 (m) cm.-1 attributed to v(OsH) and at 1906 (vs) and 1891 (s) cm.-1 attributed to v(CO). The high-field n.m.r. pattern (benzene solution) comprises a doublet of triplets indicative of the stereochemistry II. 

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