Osmium bridging hydride ligands

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.

The details for the synthesis of the activated tetraosmium hydrido cluster [Os4(/r-H)4(CO)io(NCMe)2] 72 have been previously reported the X-ray structure has now been determined. It consists of a tetrahedral metal core with each hydride ligand bridging the four OsOs bonds which are longer (2.915(3)-2.998(3) A) compared to the remaining two (both 2.810(3) A). The two acetonitrile ligands are coordinated to the same osmium atom (OsN = 2.02(4) and 2.07(5) A). The molecule possesses approximate symmetry. 

Trinuclear osmium clusters have received considerable attention recently. The green isomer of [Os3(//-H)2(CO)9(CNBu )], in contrast to the previously known red isomers, contains the CNBu ligand bonded in an axial site to the Os atom not associated with bridging hydrides. Fluxionality is associated with 3-fold rotation of the carbonyls of the Os(CO)3 units, the hydride ligands and carbonyls of the Os(CO)3(CNBu ) remaining unaffected. In the complex [ (OC)4(Bu NC)Os Os3(CO)u] there is evidence of restricted rotation about one of the Os—Os bonds at... 

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