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〉.