Proton NMR Studies of the Electronic Effect of Substituents at the Azomethine Carbon of N,N′-Bisethylene (Salicylideniminato) Cobalt (II) Complex

The proton paramagnetic shifts of low spin N,N′-ethylenebis(salicylideniminato)cobalt(II) and its derivatives were studied to understand the effect of substituents at the azomethine carbon on the electronic structure of the Schiff-base cobalt complexes. Analysis of the ¹H paramagnetic shifts of H and CH₃ bonded to the azomethine carbon reveals that spin delocalization through a interaction is responsible for the contact contribution to the paramagnetic shift. When the phenyl group is bonded to the azomethine carbon, the plane of the phenyl group is perpendicular to the plane of the complex and the phenyl group makes a negligible contact contribution to the paramagnetic shift.