Darstellung und Redoxverhalten aller bindungsisomeren Hexakis(thiocyanato(N)-thiocyanato(S))-osmate(III) und (IV), [Os(NCS)n(SCN)6-n]3-/2-, n = 0—6, einschließlich der Stereoisomeren / Preparation and Electrochemical Behaviour of All Bond-Isomeric Hexakis(thiocyanato(N)-thiocyanato(S))osmates(III) and (IV), [Os(NCS)n(SCN)6-n]3-/2-, n = 0—6, Including Stereoisomers

Abstract

Abstract The first two complete series of all 10 possible linkage and geometric isomers of the general formula [Os(NCS)n(SCN)6-n]3-/2- have been obtained. The Os(III) complexes, some of which have been previously known, are prepared from the reactions of K2[OsX6], X = Cl. Br. I, and K2[OsO2(OH)4] with excess aqueous or methanolic KSCN solution and subsequent chromato­graphic separation on DEAE cellulose. Oxidation with Ce(IV) in acetone or methanol yields the corresponding Os(IV) compounds without changes in the ligand sphere except for n = 0, but pure salts of [Os(SCN)6]2“ are isolated by repeated recrystallization. S-bonding is less favoured in Os(IV) than in Os(III), proving that Os(IV) is the harder Lewis acid. Cyclic voltammograms of all isomers show two waves, a mainly irreversible Os(II)/Os(III) couple and a reversible Os(III)/Os(IV) couple. Characteristic shifts of the half-wave potentials of both electron transfer reactions within the series give strong evidence of π-back donation to -NCS.