MIXED-LIGAND COMPLEXES OF OSMIUM(III II)8-QUINOLINOLATES WITH ONE DIIMINE AZOIMINE LIGAND/

Paramagnetic [Os(III)DQ2]+ and diamagnetic [Os(II)AQ2] (Q = deprotonat ed 8-quinolinols, D = diimines and A = azoimines) complexes were prepa red and characterised by physicochemical, magnetic and spectroscopic m ethods. The complexes exhibit several spin-allowed and spin-forbidden charge-transfer transitions in the visible region. In MeCN solution th e OsN4O2 unit displays nearly reversible Os(IV)-Os(III) and Os(III)-Os (II) couples in the ca. -0.4 to + 1.1 V range versus SCE. An anodic sh ift of these responses is seen in going from diimines to azoimines. Th e stability of metal oxidation levels is correlated on the basis of pi -acceptor properties of these ligands.