The reaction of biradical 2,6-NITpy (1) (2,6-NITpy=2,6-bis (3′-oxide-1′-oxyl-4′,4′,5′,5′-tetramethylimidazolin-2′-yl) pyridine), 2-NIT-6-IMpy (2) (2-NIT-6-IMpy=2-(3′-oxide-1′-oxyl-4′,4′,5′,5′-tetramethylimidazolin-2′-yl)-6-(1′-oxyl-4′,4′,5′,5′-tetra-methylimidazolin-2′-yl) pyridine), or 2,6-IMpy (3) (2,6-IMpy=2,6-bis(1′-oxyl-4′,4′,5′,5′-tetra-methylimidazolin-2′-yl) pyridine) with M(hfac)2·XH2O (M=MnII, CoII) were investigated. These reactions were found to be related to the type of the metal ion employed. Interestingly, redox reactions involve in the synthesis process of the complexes. Structures of the five complexes were elucidated by X-ray analysis, and their magnetic properties were investigated in detail. The temperature dependence of χMT for all the five complexes at high temperature range exhibited antiferromagnetic interactions between the transition metal spin (MnII or CoII) and the nitroxide radical spin. At low temperature, the χMT curves exhibit different magnetic behaviors because of the different crystalline fields and intermolecular interactions.