Various transition metal oxides are deposited on the surface of materials such as stainless steel, which is used in the coolant systems of nuclear power plants. The task of removing harmful radionuclides can be solved through the dissolution reaction of the deposited corrosion oxide layer. In this study, for the first time, the reaction thermodynamics of the hydrazine-based reductive metal ion decontamination (HyBRID) reaction developed by the Korea Atomic Energy Research Institute were studied considering the formation of a strong ion − ligand chemical bond complex between Cu ions and hydrazine. When considering complex formation, we found that it had a significant impact on the thermodynamic decontamination reactions of magnetite, nickel ferrite, and chromite. The reactions were proven to be much more thermodynamically favorable than the reaction energies reported thus far, which did not consider complex formation. We demonstrated that not only the thermodynamic energy but also the structures of the HyBRID reaction products can be significantly changed, depending on complex formation considerations.