The ground electronic state of quadridentate salicylaldehyde Schiff base–cobalt(II) complexes in non- and weakly co-ordinating solvents

Abstract

The isotropic shifts in the ¹H n.m.r. spectra of NN′-o-phenylenebis(salicylideneiminato)cobalt(II) have been observed in solutions of [²H]chloroform, [²H₇]dimethylformamide, [²H₆]dimethyl sulphoxide, and [²H₅]pyridine. The contact shifts derived from the isotropic shifts revealed that the unpaired electron spin is delocalized onto the ligand through the highest-filled π molecular orbital. Formation of more than one species is observed in solutions of [²H₇]dimethylformamide and [²H₆]dimethyl sulphoxide as evidenced by the electronic absorption spectra in the near-i.r. region and by the large deviation from the Curie law of the temperature dependence of the isotropic shifts. The solvent-dependent isotropic shifts indicate that π-spin delocalization in chloroform solution is an intrinsic property of the planar four-co-ordinate complex and that the ground state of the complex is |²A₂, yz〉. Co-ordination of weakly co-ordinating solvent molecules changes the ground state to |²A₁, z²〉.