An electron spin resonance study of the molecular oxygen adducts formed by the cobalt(II) chelate of salicylaldazine and related systems

Abstract

Cobalt(II) chelates, as well as those of copper(II), nickel(II), and manganese(II), of salicylaldazine, 5,5′-dichlorosalicylaldazine, 3,3′-dimethoxysalicylaldazine, and salicylaldehyde hydrazone have been prepared and characterized by elemental analysis, thermogravimetric analysis, and magnetic susceptibility measurements. The high-spin cobalt(II) chelates form reversible adducts with molecular oxygen in chloroform solutions containing various bases at room temperature. The e.s.r. spectra of the molecular oxygen adducts have been recorded using frozen solutions, and magnetic and structural parameters have been obtained by computer simulation of these spectra. The effect of substituent groups on the ligands and of the various bases present on the numerical values of the parameters is discussed. The electronic mechanisms which contribute to the hyperfine structure observed in the e.s.r. spectra of the molecular oxygen adducts have been reassessed. Within the terms of the model, indirect spin-polarization effects appear to be overshadowed by direct effects in many cases.