INFRARED SPECTROSCOPIC EVIDENCE FOR 2ND-SPHERE HYDRATION IN AQUEOUS-SOLUTIONS OF AL-3+, CR-3+, AND RH-3+

The hydration of the chromium(III), rhodium(III), and aluminum(III) ions in aqueous perchlorate solution has been studied by vibrational spectroscopy in both the OD (2900-1800 cm-1) and OH (4000-2800 cm-1) stretching regions, using an infrared absorption double-difference method. By isotopic substitution of hydrogen atoms it has been possible to extract spectra of ion-perturbed HDO molecules. The OD and OH stretching spectra contain bands that can be assigned to the first and second hydration spheres of the cations and are consistent with recent results from solution X-ray and diffusion studies.