STERIC CONTROL OF REDOX POTENTIALS OF COBALT(II) SCHIFF-BASE COMPLEXES WITH PHENYL SUBSTITUENTS

The structure of the cobalt(II) complex of the tetradentate Schiff base ligand derived from 2-hydroxybenzophenone and rac-1,2-diphenylethylenediamine was determined by the X-ray method to show that the phenyl groups in the N-N chelate moiety are in axial positions. The redox potential of the cobalt(II/III) couple in CH3CN for the complex is shifted in a more positive direction by ca. 300 mV than that for [Co-II(salen)]. The significant anodic shift is ascribed to the steric effect of the axial phenyl groups.