Dioxygen affinities of some ruthenium(III) schiff base complexes

Abstract

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(picolinaidehyde)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 ΔH° and ΔS° of oxygenation that fall in the range -6.1 to -13.3 kcal mol⁻¹ for ΔH° and -10 to -31 cal deg⁻¹ mol⁻¹ for ΔS°. The dioxygen adducts of Ru^III were characterized by electrochemistry, UV-vis, IR and EPR techniques as Ru^IV superoxo complexes.