Hydration and Ion Pair Formation in Aqueous Lu(3+)- Solution

Aqueous solutions of Lu(3+)- perchlorate, triflate and chloride were measured by Raman spectroscopy. A weak, isotropic mode at 396 cm(−1) (full width at half height (fwhh) at 50 cm(−1)) was observed in perchlorate and triflate solutions. This mode was assigned to the totally symmetric stretching mode of [Lu(OH(2))(8)](3+), ν(1)LuO(8). In Lu(ClO(4))(3) solutions in heavy water, the ν(1)LuO(8) symmetric stretch of [Lu(OD(2))(8)](3+) appears at 376.5 cm(−1). The shift confirms the theoretical isotopic effect of this mode. In the anisotropic scattering of aqueous Lu(ClO(4))(3), five bands of very low intensity were observed at 113 cm(−1), 161.6 cm(−1), 231 cm(−1), 261.3 cm(−1) and 344 cm(−1). In LuCl(3) (aq) solutions measured over a concentration range from 0.105–3.199 mol·L(−1) a 1:1 chloro-complex was detected. Its equilibrium concentration, however, disappeared rapidly with dilution and vanished at a concentration < 0.5 mol·L(−1). Quantitative Raman spectroscopy allowed the detection of the fractions of [Lu(OH(2))(8)](3+), the fully hydrated species and the mono-chloro complex, [Lu(OH(2))(7)Cl](2+). In a ternary LuCl(3)/HCl solution, a mixtrure of chloro-complex species of the type [Lu(OH(2))(8−n)Cl(n)](+3−n) (n = 1 and 2) were detected. DFT geometry optimization and frequency calculations are reported for Lu(3+)- water cluster in vacuo and with a polarizable dielectric continuum (PC) model including the bulk solvent implicitly. The bond distance and angle for [Lu(OH(2))(8)](3+) within the PC are in good agreement with data from structural experiments. The DFT frequencies for the Lu-O modes of [Lu(OH(2))(8)](3+) and its deuterated analog [Lu(OD(2))(8)](3+) in a PC are in fair agreement with the experimental ones. The calculated hydration enthalpy of Lu(3+) (aq) is slightly lower than the experimental value.