Hydration and Ion Pair Formation in Aqueous Lu³⁺- Solution.

Area of Science:

• Inorganic Chemistry
• Solution Chemistry
• Spectroscopy

Background:

• Lutetium (Lu³⁺) is a lanthanide ion with significant applications.
• Understanding the hydration and complexation of Lu³⁺ in aqueous solutions is crucial for its chemical behavior.
• Raman spectroscopy is a powerful tool for probing the vibrational modes of ions in solution.

Purpose of the Study:

• To investigate the structure and speciation of Lu³⁺ in aqueous perchlorate, triflate, and chloride solutions using Raman spectroscopy.
• To identify the hydrated species and any chloro-complexes formed.
• To compare experimental results with theoretical calculations.

Main Methods:

• Raman spectroscopy of aqueous Lu³⁺ solutions (perchlorate, triflate, chloride) at various concentrations.
• Measurements in both H₂O and D₂O to confirm isotopic effects.
• Density Functional Theory (DFT) calculations for geometry optimization and frequency analysis.

Main Results:

• The symmetric stretching mode (ν₁LuO₈) of the [Lu(OH₂)₈]³⁺ complex was identified at 396 cm⁻¹ in perchlorate and triflate solutions.
• A shift to 376.5 cm⁻¹ in D₂O confirmed the isotopic effect for [Lu(OD₂)₈]³⁺.
• In LuCl₃ solutions, a 1:1 chloro-complex ([Lu(OH₂)₇Cl]²⁺) was detected, along with mixed chloro-complexes ([Lu(OH₂)_8-nCl_n]^+3-n, n=1,2) in ternary solutions.
• DFT calculations supported the experimental findings regarding bond distances, angles, and vibrational frequencies.

Conclusions:

• The dominant species in dilute aqueous Lu³⁺ solutions is the octa-hydrated ion, [Lu(OH₂)₈]³⁺.
• Chloride ions can form mono- and di-chloro complexes with Lu³⁺ in solution.
• Raman spectroscopy and DFT calculations provide complementary insights into the hydration and complexation of Lu³⁺.