Osmium tetravalent complexes

Although both the brown [Os(NH3)6] and the yellow [Os(NH3)6]Br have been claimed as products of the reaction of [Os(NH3)6]Br3 with potassium in liquid ammonia,54 the products were not well characterized and could be hydrido ammines or mixtures. There is evidence from the polarographic reduction of [Os(NH3)6]3+ for the existence of [Os(NH3)6]2+ but it appears to be labile to substitution and has not been isolated 55 in this respect osmium differs significantly from ruthenium, for [Ru(NH3)6]2+ is isolable and is in fact a useful synthetic precursor. The tetravalent complex [Os(NH3)s]4+ has also been detected electrochemically, by cyclic voltammetric oxidation of [Os(NH3)6]3+ 55 in acidic solution however, the first product of one-electron oxidation of [Os(NH3)s]3+ is probably [Os(NH3)s(NH2)]3+.ss... 

As ligands for osmium, ammonia and ethylenediamine (en 1,2-diaminoethane) would be expected to have broadly similar properties, and this is on the whole true — there are stable osmium(III) complexes such as [Os(en)3]3+, trans-[Os(en)2 X2]+ (X — Cl, Br) and [Os(en)Cl4], and more recently the tetravalent Os(en)X4 (X = Cl, Br, I) has been made. There is, however, an interesting chemistry of the l,2-ethanediaminato-(l —) and -(2 —) ligands with osmium in the higher IV, V and VI states, and another unusual feature is the existence of the hydride [OsH2(en)2f. ... 

All three elements form complex ammino-derivatives. Those of osmium have been very little investigated those of iridium are analogous to the anunino-derivatives of platinum on the one hand and to the ammincs of cobalt and chromium on the other whilst the platinum derivatives resemble those of cobalt, save that the metal in the platinic derivatives is tetravalent and not trivalent as in the cobalt-ammines. 

A new class of binuclear nitrido complexes of tetravalent osmium and ruthenium is described in which the metal atoms are symmetrically bridged by a nitride ligand to give a linear M-N—M unit They have the stoichiometries M2NX8(H20)2]3 and [M2N(NH3)8Y2]3+ (M = Os, Ru X = Cl, Br Y = Cl, Br, etc.). Studies are reported on their vibrational spectra, structures, and bonding. Preliminary studies are reported also on trinuclear complexes of osmium and iridium. Finally, the use of vibrational spectroscopy in the study of metal-nitrido and metal-oxo complexes is discussed briefly. 

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