Terahertz absorption spectra of some saccharides and their metal complexes

In this work, THz absorption spectra of some saccharides and their metal complexes were measured. The main purpose of this work is to investigate the M–O vibrations, intermolecular and intramolecular hydrogen bonds and other vibrations in the FIR region using powerful spectroscopic techniques adopting the metal–sugar complexes prepared in our laboratory. The M–O vibrations in the FIR spectra of metal–sugar complexes indicate the formation of metal complexes. The THz spectrum of glucose below 100 cm−1 was measured at first to confirm the THz experimental method. Characteristic absorption bands in the spectra of various samples are observed. THz spectra of saccharides below 100 cm−1 often have several absorption bands, and different saccharides have various absorption peaks in the THz region, which may be used to distinguish different saccharides. The differences in the number of bands observed are related to different structures of the samples, and these absorption bands are related to the collective motion of molecules. But the THz spectra of their metal complexes are different from the ligands, and no band appears in the region below 50 cm−1 at the present experimental condition, which indicates that THz spectroscopy may also be helpful to identify the formation of metal–sugar complexes, and the changes after complexation in the THz spectra below 100 cm−1 may be related to different metal ions. The metal–sugar complexes with similar crystal structures resemble mid-IR spectra, but their THz spectra may have some differences.