Osmium sulfur donor ligands

The 0x0 (0 ) ligand is dominant in the coordination chemistry of osmium, participating in the VIII to IV oxidation states inclusive. The tetroxide OSO4 is the single most important compound of osmium OSO4 and the recently discovered [0s04] ion arc tetrahedral. The /ra 5-[0=0s —O] osmyl moiety displays an extensive chemistry, comparable with that of the uranyl 0=U=0 unit, and there is an extensive and unique cyclic oxo-ester chemistry (p. 584). There is surprisingly little information on hydroxo, aqua, sulfato, nitrato or phosphato complexes, but much recent work has been carried out on carboxylato species, and clearly much work remains to be done on the O-donor chemistry of the element. There are a reasonable number of sulfur-donor complexes but few with selenium or tellurium. 

NMR all three osmium atoms are chemically equivalent (200). This may involve changing the bridging sulfur atom from a four-electron donor to a two-electron donor in order to gain a third Os-Os bond and an equilateral metal triangle. These ligand induced cluster rearrangements are a further demonstration of metal-metal bond weakness as the reason for cluster mobility. For application-oriented purposes they may be the most important ones. 

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