Dear Dr. Nizam.. The chemistry of Co is very close to Ni, Fe and perhaps any ligand that coordinates with Co may do the same with Fe or Ni. The stability of the formed complexes are definitely not the same. Thus, whenever a method for the determination of Ni, or Co based on complexometry is established, a study of the interference from the other adjacent transition metal ions must included. However, there are still some ligands that show specific tendency to complex cobalt. For Ni we have dimethyl glyoxime. For Co, I must refer to a book in my collection and a strong answer will be available for your question. Of course, the oxidation state, whether 2, or 3, must be specifid. Regards
You can choose the option most suitable for you. The higher the value of pK, the more stable complex compound. Cobalt in oxidation state , typically provides a more stable complex compound than in oxidation state .
I have been devoted in recent years to thermal-treating of various copper complexes. In general, ligands could coordinate with Co ions as well as that of Cu ions. The key point is the water solubility of complex agents.You could find more details in my publications which have been uploaded here.