The absorption peaks around 1625 cm⁻¹ and 1392 cm⁻¹ can be attributed to the bending vibrations of the O-H bond, along with vibrations from methylene (-CH₂) or methyl (-CH₃) groups present in compounds such as fatty acids and polyphenols within the extract . In the intermediate copper complex, the band at 1625 cm⁻¹ corresponds to the C=C aromatic bending vibration , while the band at 1392 cm⁻¹ is attributed to the stretching interactions between copper and oxygen atoms . The stretching peak at 1272 cm⁻¹ is characteristic of both symmetrical and functional groups, such as ethers or phenolic acids . Additionally, the absorption peak at 1072 cm⁻¹ in the yerba mate extract is assigned to the stretching vibration of the C-OH side group .