The already reported monomeric complex Co(SDZ) 2 bpy ( 1 ) and the new ternary complex Co(SDZ) 2 (6MQ) 2 ( 2 ) (SDZ = sulfadiazine, bpy = 2,2′‐bipyridine, and 6MQ = 6‐methoxyquinoline) have been synthesized in order to study their magnetic properties. X‐ray diffraction studies indicate that in both compounds the SDZ acts as a bidentate ligand coordinating through the sulfonamide and the pyrimidine N atoms giving rise to a CoN 6 coordination sphere. The complexes have been characterized based on elemental analyses, FTIR, UV/Vis spectroscopy, and thermogravimetric analysis (TGA, only for 2 ). Compounds 1 and 2 have been characterized magnetically, and they show slow relaxation of the magnetization below 9 and 6 K, respectively.