Cis and trans forms of O S ( N H~)~X~~+ and of r n e r -0~( N H , )~X , (where X is CI, Br, or I) were prepared by oxidizing the corresponding Os(II1) complexes with Fe3+(aq). Acidic solution aquation and disproportionation are sufficiently slow so that ion-exchange methods are applicable to separations and characterization. The osmium(1V) ammines in comparison to the corresponding Os(II1) species show LMCT at lower energies and metal to halide stretching frequencies ca. 40 cm-' higher. At high enough acidity the Os(IV)/Os(III) couples are reversible in cyclic voltammetry. Application of this method yielded Ef values for tr~ns-[Os(NH,)~C1,], ~is-[0s(NH,)~Cl,], rner-[Os(NH,),C13], and OsNH,CIS of 0.73, 0.83, 0.61, and 0.37 V, respectively. As the pH is raised, the values of Ef become acid dependent. A combination of electrochemical and spectrophotometric measurements yielded pK, values for the four chloro complexes of 4.0, -1, 4.9, and 6.5, respectively.The relatively higher acidity of the osmium(1V) ammines compared to that of Pt(IV) analogues is attributed to charge transfer from ligands to the unfilled ?r orbitals of Os(1V).
Die Oxidation von [Os(NH3)5(CO)](2+) durch Ce(IV) in saurer Lösung bei einem Molverhältnis der Reaktionspartner von 1.0 oder etwas weniger liefert beinahe quantitativ den zweikernigen μ‐Distickstoff‐Titelkomplex mit cis‐Struktur.
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