High potential isomeric dihalobis[2-(arylazo)pyridine] osmium(III) perchlorate monohydrate

Summary The preparation of isomeric complexes Os^IIIX₂L₂]ClO₄· H₂O {(4)} and (5): X = Cl or Br, L(1) = 2-(phenylazo)-pyridine (L¹) or 2-(m-tolylazo)pyridine(L²)] via stereo-retentive oxidation of the corresponding osmium(II) precursors (2) and (3), respectively] is described. The complexes were characterized using spectroscopic and electrochemical methods. The low-spin (idealized t _2g ⁵ ; S = 1/2) paramagnetic complex ions display characteristic osmium(III) e.p.r. spectra in frozen (-196° C) MeCNPhMe. In dry MeCN solution, the OsX₂N₄ unit exhibits irreversible OsX₂L₂]²⁺/OsX₂L₂]⁺ and reversible OsX₂L₂]⁺/OsX₂L₂] couples at ca. 1.8 and 1.0 V versus saturated calomel electrode (s.c.e.), respectively. The use of (4)/(5) as an oxidant is noted.