Hydration and Ion Pair Formation in Aqueous Lu- Solution.

Aqueous solutions of Lu- perchlorate, triflate and chloride were measured by Raman spectroscopy. A weak, isotropic mode at 396 cm (full width at half height (fwhh) at 50 cm) was observed in perchlorate and triflate solutions. This mode was assigned to the totally symmetric stretching mode of [Lu(OH₂)₈], ν₁LuO₈. In Lu(ClO₄)₃ solutions in heavy water, the ν₁LuO₈ symmetric stretch of [Lu(OD₂)₈] appears at 376.5 cm. The shift confirms the theoretical isotopic effect of this mode. In the anisotropic scattering of aqueous Lu(ClO₄)₃, five bands of very low intensity were observed at 113 cm, 161.6 cm, 231 cm, 261.3 cm and 344 cm. In LuCl₃ (aq) solutions measured over a concentration range from 0.105⁻3.199 mol·L a 1:1 chloro-complex was detected. Its equilibrium concentration, however, disappeared rapidly with dilution and vanished at a concentration < 0.5 mol·L. Quantitative Raman spectroscopy allowed the detection of the fractions of [Lu(OH₂)₈], the fully hydrated species and the mono-chloro complex, [Lu(OH₂)₇Cl]. In a ternary LuCl₃/HCl solution, a mixtrure of chloro-complex species of the type [Lu(OH₂)Cl] ( = 1 and 2) were detected. DFT geometry optimization and frequency calculations are reported for Lu- water cluster in vacuo and with a polarizable dielectric continuum (PC) model including the bulk solvent implicitly. The bond distance and angle for [Lu(OH₂)₈] within the PC are in good agreement with data from structural experiments. The DFT frequencies for the Lu-O modes of [Lu(OH₂)₈] and its deuterated analog [Lu(OD₂)₈] in a PC are in fair agreement with the experimental ones. The calculated hydration enthalpy of Lu (aq) is slightly lower than the experimental value.