Under these conditions, rather than forming copper hydroxide initially, a metal complex is formed between copper and the organic constituents of the extract . The acidity of the medium, influenced by the extract, facilitates this complexation of copper ions with the bioactive compounds present in yerba mate, leading to the formation of a reaction intermediate . Copper oxide nanoparticles are then formed after calcination at 400 °C. X-ray diffraction (XRD) analysis of the metal complex (Figure ) reveals amorphous behavior, corroborating the presence of the reaction intermediate.