Résumé
Infrared spectroscopy has been used to study the molecular structure of lanthanide dithizonate. By comparing the complex spectra with that of dithizone, it was found that, new bands appeared at about 3222, 446 and 247 cm' in the spectra of all samples except that of dysprosium dithizone. The first band was assigned as N-H stretching vibrations, the second and third bands are assigned as M-N and M-S stretching vibrations, respectively. The disappearance of NH band for dithizone excludes the tautomeric thione and thiol structures, and supports the open ring structure. The disappearance of this band in dysprosium dithizone indicates that an ionic redistribution reaction takes place giving a mixture during crystallization process. Also, the appearance of NH stretching vibration for dithizone complexes indicates that the complex form is primary one. The second and third bands approve that, the lanthanide cation coordinated with the nitrogen and sulfur atoms. A considerable frequency shift and splitting were observed for some of the vibrational bands as a result of complex formation. The effect of complex formation upon wavenumber and intensity were studied in details for [NH], [MN] and [MS]. The wavenumber increases with increasing the number of electron in 4f orbital and atomic weight while it decreases with increasing ionic radius of the lanthanide cations. The gadolinium complex has abnormal behaviour; this may be due to the highly electrostatic nature of its cation