Mixed-ligand complexes of osmium(III)/(IV) 8-quinolinolates: synthesis,characterization and redox behaviour

Summary A group of mixed-tris chelates of osmium(III) and osmium(IV) of type OsAQ₂]^{0/1 +} HA = glycine (glyH), picolinic acid (PicH) and quinaldic acid (qndH); HQ = 8-quinolinol] were prepared and characterized by physicochemical, magnetic and spectroscopic methods. The complexes exhibit several spin-allowed and spin-forbidden absorption bands and shoulders in the 200–700 nm region. The new chelates are electroactive and display nearly reversible Os^IV-Os^III and Os^III-Os^II couples in the ca. –1.1 to +0.3 V range versus s.c.e. The stability of metal oxidation states is discussed in terms of the electrochemical results.