Hydration and Ion Pair Formation in Aqueous Lu<sup>3+</sup>- Solution
Wolfram Rudolph, Gert Irmer
Molecules · 2018
doi:10.3390/molecules23123237 (opens in a new tab)
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Abstract
Aqueous solutions of Lu<sup>3+</sup>- perchlorate, triflate and chloride were measured by Raman spectroscopy. A weak, isotropic mode at 396 cm<sup>−1</sup> (full width at half height (fwhh) at 50 cm<sup>−1</sup>) was observed in perchlorate and triflate solutions. This mode was assigned to the totally symmetric stretching mode of [Lu(OH<sub>2</sub>)<sub>8</sub>]<sup>3+</sup>, ν<sub>1</sub>LuO<sub>8</sub>. In Lu(ClO<sub>4</sub>)<sub>3</sub> solutions in heavy water, the ν<sub>1</sub>LuO<sub>8</sub> symmetric stretch of [Lu(OD<sub>2</sub>)<sub>8</sub>]<sup>3+</sup> appears at 376.5 cm<sup>−1</sup>. The shift confirms the theoretical isotopic effect of this mode. In the anisotropic scattering of aqueous Lu(ClO<sub>4</sub>)<sub>3</sub>, five bands of very low intensity were observed at 113 cm<sup>−1</sup>, 161.6 cm<sup>−1</sup>, 231 cm<sup>−1</sup>, 261.3 cm<sup>−1</sup> and 344 cm<sup>−1</sup>. In LuCl<sub>3</sub> (aq) solutions measured over a concentration range from 0.105⁻3.199 mol·L<sup>−1</sup> a 1:1 chloro-complex was detected. Its equilibrium concentration, however, disappeared rapidly with dilution and vanished at a concentration < 0.5 mol·L<sup>−1</sup>. Quantitative Raman spectroscopy allowed the detection of the fractions of [Lu(OH<sub>2</sub>)<sub>8</sub>]<sup>3+</sup>, the fully hydrated species and the mono-chloro complex, [Lu(OH<sub>2</sub>)<sub>7</sub>Cl]<sup>2+</sup>. In a ternary LuCl<sub>3</sub>/HCl solution, a mixtrure of chloro-complex species of the type [Lu(OH<sub>2</sub>)<sub>8−n</sub>Cl<sub>n</sub>]<sup>+3−n</sup> (<i>n</i> = 1 and 2) were detected. DFT geometry optimization and frequency calculations are reported for Lu<sup>3+</sup>- 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<sub>2</sub>)<sub>8</sub>]<sup>3+</sup> within the PC are in good agreement with data from structural experiments. The DFT frequencies for the Lu-O modes of [Lu(OH<sub>2</sub>)<sub>8</sub>]<sup>3+</sup> and its deuterated analog [Lu(OD<sub>2</sub>)<sub>8</sub>]<sup>3+</sup> in a PC are in fair agreement with the experimental ones. The calculated hydration enthalpy of Lu<sup>3+</sup> (aq) is slightly lower than the experimental value.
Abstract licence: CC BY
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