Vibrational and electronic studies on interactions of Cu (II) with protic amides: Structural aspects of biological importance

Raman, IR and UV-Vis-NIR experiments of formamide (FA), N-methylformamide (NMF) and their solutions with copper perchlorate at different compositions were carried out. The downshift of the νCO mode and the upshift of the νCN vibration have been observed for both amides and suggest that an ionic structure is stabilized by Cu (II). The quantitative Raman study at the νCN region reveals that six FA molecules are coordinated to Cu (II) while four NMF molecules are around the metal ion. The data are complemented by information at the region characteristic of the metal-ligand vibrations, which evidences coordination through the O atom. The spectral changes observed at the νCN region have been then combined to the electronic data and show that [Cu(FA)6]2+ and [Cu(NMF)4]2+ are described as distorted octahedral and square planar complexes.