Other Osmium Complexes

Osmium forms a 6-coordinate acetylacetonate, Os(acac)3, isomorphous with the ruthenium analogue unlike ruthenium, however, the osmium(IV) complexes Os(acac)2X2 (X = Cl, Br, I) can be made (cis- and frans-isomers exist) from OsXg- and Hacac, as can Os(acac)X [176]. 

The pyridine complexes of osmium(III) result from reductive substitution 

The osmium(IV) complexes can be made by oxidation of the osmium(III) systems [152]  

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Osmium(III). The osmium(III) complexes K[Os(LL)C14] (LL = bipy, phen), made by reduction of Os(LL)C14 with H3P02 and KC1, are useful precursors for other osmium complexes (Scheme 4). In general, osmium(III) complexes in this category are made by oxidation of the corresponding osmium(II) species with chlorine or with cerium(IV) (see Schemes 3 and 4). 

There are also bis(dinitrogen) complexes of osmium(II). The first to be made was cis-[Os(N2)2(NH3)4]2+ by a diazotization procedure using [Os(N2)(NH3)5]2" and nitrite in acid solution.270 Vibrational spectroscopic data using both 2H and 15N substitution were obtained for the salts,271 which are useful precursors for other osmium complexes involving pyrazine (see p. 536). A similar preparative procedure involving [Os(N2)(NH3)4L]2+ gives m-[Os(N2)2(NH3)3L]2+ (L = isonicotinamide).98... 

Salts of [Os(bpy>3] are best prepared by the reaction of bpy with [Os(bpy)2Cl2] (102) or by prolonged reaction with other osmium complexes (56, 318, 621). The crystal structure of [Os(bpy)3][PF6]2 reveals identical molecular properties to the corresponding ruthenium complex (159). Studies of the and NMR spectra of [Os(bpy>3] + salts... 

Reviewed in this section is the chemistry of Os3(CO),2, OsH2Cl2(P Pr3)2, Os(/ -MeC6H4CHMe2)(N Bu), NaiOsCl, 0s04and osmium carbene complexes. Reviews of other osmium complexes are available [224-225]. 

Salts of [OsXfl] , especially the chloride as Na2[0sCl6] H2 0 (conveniently soluble in water or polar organic solvents), as K2[OsCl( ] or (NH4)j[OsClj], are good precursors for preparations of other osmium complexes indeed, Na2[0sCl6]-nH2 0 rivals OSO4 as a useful starting material. 

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