Osmium time series

A large number of HNCC of osmium have been produced from the vacuum pyrolysis of Os3(CO)i2 and some of its derivatives (Scheme 1). The reaction of Os3(CO)i2 has been shown to be extremely sensitive to temperature, time, and moisture, giving a series of products whose nuclearities range from 5 to 11 and possibly higher 41, 54, 80, 134). By optimizing the conditions, yields up to 80% of Os6(CO)ig have been obtained 41). High specificity has also been observed in the vacuum pyrolysis of Os3(CO)ii(C5H5N), from which [OsioC(CO)24j] has been obtained in 65% yield 80). 

Density. Atomic size, and therefore volume, is inversely related to density. Across a period, densities increase, then level off, and finally dip a bit at the end of a series (Figure 22.4D). Down a transition group, densities increase dramatically because atomic volumes change little from Period 5 to 6, but atomic masses increase significantly. As a result, the Period 6 series contains some of the densest elements tungsten, rhenium, osmium, iridium, platinum, and gold have densities about 20 times that of water and twice that of lead. 

A series of carbonyl-substituted osmium clusters of general formula Os6(CO)2i-. Lv (L = P(OMe)3, X = 1-6 L = MeCN, x = 1-3) is also structurally related to [Fe3Pt3(CO)i5] and features six extra cluster-valence electrons. As predicted theoretically,these raft-like osmium clusters have a similar capacity to add two more electrons reversibly. The electro-generated anions are stable on the cyclovoltammetry time-scale. 

Systematic investigations of series of ruthenium (II) (7, 8, 9, 10), osmium (II) (II), and iridium (III) (12) complexes led to the experimental and theoretical characterization of CTTL excited states. Their properties, derived from analyses of spectra, decay times, and interactions with external fields, diflFer fundamentally from the excited states of organic materials and even from states of other orbital parentages within the same molecule. 

S. Tennant, like W. Wollaston, dissolved crude platinum in aqua regia. At the bottom of the retort he discovered a black precipitate with metallic lustre. This phenomenon had been observed previously in experiments with platinum, but the precipitate was believed to be graphite. In summer 1803 Tennant suggested that the precipitate most likely contained a new metal. In autumn of the same year the French chemist H. Collet-Descoties also concluded that the precipitate contained a metal that precipitated from ammonium platinum salts and yielded red colour. In his turn, L. Vauquelin heated the black powder with alkali and obtained a volatile oxide. Vauquelin believed that it was an oxide of the metal mentioned by H. Descoties. Tennant s experiment set off a series of investigations. Tennant himself continued his research and in spring 1804 he reported to the British Royal Society that the powder contained two new metals which could be separated fairly easily. In 1805 he published the article On Two Metals Found in the Black Powder Formed after Dissolution of Platinum . The names osmium and iridium were mentioned in the article for the first time. 

In the 1920 s, E. MQller and his co-workers made a series of studies on the anodic oxidation of methanol, formaldehyde, and formic acid which represent the first extensive mechanistic investigation of these compounds, although the principles of electrode kinetics had not yet been formulated. Muller did not establish mechanisms for these reactions however, many of his observations have been later confirmed and his studies were among the first with a comparison of polarization curves on several noble metals including platinum, palladium, rhodium, iridium, osmium, rubidium, gold, and silver (cf. Figure 1). As was usual at that time, Muller discussed his results in terms of polarization, rather than in terms of current or reaction rate. 

Dehydration of the tertiary alcohol (290) led to a miicture of approximately equal amounts of the A - and A -isomers (293) and (294) when it was oxidized with osmium tetroxide, all four theoretically possible isomers of the cis-diols (292) and (298) were obtained. At the same time, both in the case of the 16,17-diols (292) and in the case of the 17,17a-diols (298) the amount of the o -isomer was the greater. The cleavage of the first pair of diols (292) with periodic acid led to the ketoaldehyde (295), which, on being boiled in xylene with triethylammonium acetate, cyclized to form dl-5a-A -pregnen-3/S-ol-20-one acetate (296), identical in respect of its IR and UV spectra with the d-enantiomer obtained from natural sources. By a similar series of reactions, the second pair of diols (298) gave the keto-acetate (297) with an acetyl group at Cjg, isomeric with (296) [648, 649,... 

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