MIXED-LIGAND COMPLEXES OF RUTHENIUM(II) AND OSMIUM(II)-2-(ARYLAZO)PYRIDINES WITH ONE 2,2'-BIPYRAZINE 2,2'-BIPYRIMIDINE - SYNTHESIS, SPECTRA AND ELECTROCHEMISTRY

A series of mixed-tris complexes of general formula [ML'L2](ClO4)2.H2O [M = Ru or Os; L' = 2,2'-bipyrazine (bpyz) or 2,2'-bipyrimidine (bpym) and L = 2-(phenylazo)pyridine (papy) or 2-(m-tolylazo)pyridine (tapy)] has been prepared and characterized by physicochemical and spectroscopic methods. Using H-1 NMR results (delta(Me) of tapy), stereochemistry of ML2 fragment in these tris chelates has been determined. The complexes show a number of MLCT transitions in the visible region; the low intensity spin-forbidden transitions are observable in osmium complexes. In MeCN solution, the OsN6 unit displays one metal-centred oxidation and multiple ligand-based reductions. Relative pi-acceptor ability of the ligands is clearly reflected in the electrochemical results.