Osmium carbonyls structures, 901

Most of the chemistry of Os3(CO)12 has been learned since 1970, and a review on osmium carbonyls in 1975 contains only a little triosmium chemistry (5). Comprehensive Organometallic Chemistry (1982) includes several times more material and cites 82 X-ray structures of triosmium compounds... 

The structures of osmium carbonyl compounds vary with an increase or decrease of the valence electrons. 

HOs6(CO)18] and H2Os6(CO)18 marks one of the highlights of the early period of osmium carbonyl cluster chemistry [162]. While both the dianionic cluster and the monoanionic system have the expected octahedral metal core, a capped square based pyramidal structure was found for H2Os6(CO)18. This turned out to be the archetypal example for the capping rule , a concept which proved to be very successful in the analysis of the structures of metal carbonyl clusters of the iron and cobalt triads [166],... 

Fig. 4.11 The metal cores of a series of structurally characterized tetrahedral osmium carbonyl clusters (I [H2Os4(CO)12]2 II [Os10C(CO)24]2 III [Os20(CO)40]2 from ref. 173 reproduced with permission of the Royal Society of Chemistry)...

An orange-yellow osmium carbonyl compound is heated to release CO and leave elemental osmium behind. Treatment of 6.79 g of the compound releases 1.18 L CO(g) at 25°C and 2.00 atm pressure. What is the empirical formula of this compound Propose a possible structure for it by comparing with the metal carbonyls shown on the right. 

Osmium catalysts prepared principally from osmium carbonyls, supported on alumina, have also been found to show antipathetic structure sensitivity (308). 

Triply bridging thiolate complexes of osmium carbonyl clusters are less common than for iron. The [Os3(CO)9(//-H)(/i3-SR)] complexes (R = Me, Et) are unstable but can be conveniently trapped as ethylene adducts subsequent regeneration of the parent complexes is facile. The X-ray structure of one such 7r-coordinated ethylene adduct, [Os3(CO)9(//-C2H4)(/r-H)(//3-SMe)], has been reported. " Very few examples of Ru clusters with 3-SR coordination (R = Bu, Pr ) have been reported in the literature. ... 

Nine neutral osmium carbonyl clusters, Os j(CO)3,., are known to us to have been structurally characterized, only one of which, Os3(CO)i2, has been the subject of a... 

The dinuclear iron carbonyl Fe2(CO)9, incidentally, has no osmium counterpart Os2(CO)9, perhaps because one or more of the ligands therein would need to play a bridging role (an unsymmetrical, polar unbridged structure (CO)40sOs(CO)5 would be extremely unlikely). If Os2(CO)9 could be prepared, reference to Fig. 2 suggests that it would be expected to contain a metal-metal bond of enthalpy 81 kJmol and length 297 pm. Other predictions about further osmium carbonyls yet to be prepared are to be found elsewhere. ... 

Figure 6. The structures of the osmium carbonyl clusters discussed in this work , Os(CO)4 , Os(CO)3 , Os(CO)2 , Os(CO). Hydride and bridging carbonyl ligands are drawn explicitly.

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