DIOXYGEN AFFINITIES OF SOME RUTHENIUM(III) SCHIFF-BASE COMPLEXES

The synthesis and dioxygen affinities of some ruthenium(III) Schiff base complexes in DMF solution in the presence of different axial bases are reported. The ligands used are bis(salicylaldehyde)ethylenediimine (salen), bis(salicylaldehyde)diethylenetriimine (saldien), bis(picolinaldehyde)-o-phenylenediimine (picoph), bis(picolinaldehyde)ethylenediimine (picen) and bis(picolinaldehyde)diethylenetriimine (picdien). The axial ligands employed are chloride (Cl-), imidazole (Im) and 2-methylimidazole (2-MeIm). From the oxygenation constants it is found that electron donating substituents on the Schiff bases increase the affinity for dioxygen. Equilibrium dioxygen uptake measurements at 278, 288 and 303 K provide values of DELTA-H-degrees and DELTA-S-degrees of oxygenation that fall in the range -6.1 to -13.3 kcal mol-1 for DELTA-H-degrees and -10 to -31 cal deg-1 mol-1 for DELTA-S-degrees. The dioxygen adducts of Ru(III) were characterized by electrochemistry, UV-vis, IR and EPR techniques as Ru(IV) superoxo complexes.