Heteroligand o-Semiquinonato Cobalt Complexes of 3-Cyano and 3-Nitroformazans

The synthesis of four heteroligand o-semiquinonate cobalt complexes of bidentate 3-cyano- and 3-nitroformazans is described. All complexes are characterized by single-crystal X-ray diffraction and magnetic susceptibility measurements. The square-planar mono-o-semiquinonato-formazanate cobalt(II) complexes demonstrate diamagnetic properties due to strong intramolecular antiferromagnetic metal-ligand exchange. Magnetic properties of the six-coordinated bis-o-semiquinonato-formazanate cobalt(III) complexes indicate the domination of antiferromagnetic exchange interactions between unpaired electrons of o-semiquinonato ligands, and the inclusion of electron-withdrawing cyano and nitro groups at R-3 position of formazanate ligand leads to an increase of the energy of this exchange interaction.