An electron spin resonance study of the oxygenation of a quadridentate thiosalicylideneimine cobalt(II) chelate

Abstract

E.s.r. spectroscopy has been used to show that the cobalt(II) chelate of NN′-ethylenebis(thiosalicylideneiminate)(tsalen) binds ligands such as pyridine and dioxygen at low temperatures in frozen solutions. At ambient temperatures the complex reacts only very weakly with these ligands and no crystalline adducts are obtained; this contrasts markedly with the behaviour of [Co(salen)][salen =NN′-ethylenebis(salicylideneiminate)] a well known oxygen-carrier. Detailed computer simulation of the spectral line shapes have been made from which a value for the Co–O–O angle in the dioxygen adduct has been deduced as well as accurate values of the g and A parameters. Reasons for the differences in the strength of axial ligand binding by the thio- and oxo-Schiff-base chelates are briefly discussed.