Two novel heteroligand o-semiquinonatoformazanto cobalt complexes [Co(3,6-SQ) (Form)] (1) and [Co(3,6-SQ)(2)(Form)] (2) (3,6-SQ 3,6-di-tert-butyl-o-benzosemiquinonate radical anion; Form is 1,3,5-triphenylformazanate anion) were synthesized and characterized in detail. The molecular structures of [Co(3,6-SQ)(Form)] and [Co(3,6-SQ)(2)(Form)] were determined by X-ray analysis. Magnetic susceptibility measurements and spectroscopic studies have shown that square-planar complex 1 is diamagnetic with a residual paramagnetism due to antiferromagnetic exchange metal-ligand. Complex 2 includes cobalt(III) in the low-spin state and two anionic-radical o-semiquinonato and one formazanate ligand.