Trans-Dioxo osmium

Monooxo and cis- and trans-6ioxo complexes of ruthenium(VI) and osmium(VI) are known, with the trans-6ioxo species being most common. In general, these complexes are all diamagnetic and are characterized by vibrational spectroscopy and/or X-ray crystallography. One intense metal-0x0 stretch is usually observed for monooxo and trans-dioxo complexes while two metal-oxo stretches, j/s(M(0)2) and J/as(M(0)2), are found for the cw-dioxo species in the IR spectra. The structural and vibrational data are listed in Table 4. 

Many osmyl complexes with group VI ligands have been reported. The purple diamagnetic potassium osmate K2[0s(0H)4(0)2] is the best known and is a useful starting material for the preparation of other osmyl or osmium complexes. It is best prepared from the reaction of 0s04 with excess KOH. The X-ray crystal structure of K2[0s(0H)4(0)2] shows that the complex has the trans-dioxo unit, with a d(0s=0) of 1.77 A and a 0=0s=0 angle of 180° (238,239). The acid dissociation constants of H2[0s02(0H)4] have been determined. 

Kelly, C. Szalda, D. J. Creutz, C. Schwarz, H. A. Sutin, N. Electron transfer barriers for ground- and excited-state redox couples trans-dioxo(l,4,8,ll-tetramethyl-l,4,8,l 1- tetraazacyclo-tetradecane) osmium(VI)/osmium(V). Inorg. Chim. Acta 1996, 243, 39-45. 

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