Abstract
Aqueous solutions of Lu3+- 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&sub2;)₈]3+, ν&sub1;LuO₈. In Lu(ClO&sub4;)&sub3; solutions in heavy water, the ν&sub1;LuO₈ symmetric stretch of [Lu(OD&sub2;)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&sub4;)&sub3;, 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&sub3; (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&sub2;)₈]3+, the fully hydrated species and the mono-chloro complex, [Lu(OH&sub2;)₇Cl]2+. In a ternary LuCl&sub3;/HCl solution, a mixtrure of chloro-complex species of the type [Lu(OH&sub2;)8-nCln]+3-n (n = 1 and 2) were detected. DFT geometry optimization and frequency calculations are reported for Lu3+- 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&sub2;)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&sub2;)₈]3+ and its deuterated analog [Lu(OD&sub2;)₈]3+ in a PC are in fair agreement with the experimental ones. The calculated hydration enthalpy of Lu3+ (aq) is slightly lower than the experimental value.