Solvation of potassium 5-hydroxy pentanoyl trifluoroborate salt in aqueous environment by using ft-raman and uv-visible spectra

Abstract

The hydration process of potassium 5-hydroxypentanoyltrifluoroborate salt, K[C5H9BF3O2] and its 5-hydroxypentanoyltrifluoroborate [C5H9BF3O2]- anion have been studied by combining the experimental FT-Raman and ultraviolet-visible spectra in aqueous solution with hybrid B3LYP/6-311++G** calculations. Solvent effects have been considered with the self-consistent reaction field (SCRF) and solvation (SM) models. Here, the structures of [C5H9BF3O2].[H2O]n clusters of anion, with n from 1 to 5 implicit water molecules, were proposed in order to study the number of water molecules that could hydrate the anion. Calculations were performed in the gas phase and an aqueous solution to observe the effect of the medium on the dipole moment and volume values. Calculated solvation energies for all clusters were corrected by zero-point vibrational energy (ZPVE), non-electrostatic terms and by basis set superposition energy (BSSE). The dipole moment of salt in solution (10.19 D) suggests that the number of water molecules that could hydrate the anion vary between 3 and 4, in total agreement with the observed and predicted bands in the UV-Vis spectra for the salt and these two clusters in water between 180 and 400 nm. Comparisons among experimental and predicted Raman spectra show clearly the hydration effect because the bands attributed to OH, BF3 and C=O groups are shifted in solution, while, the predicted Raman spectra for all clusters in solution show strong changes in the intensities of many bands, in accordance with the corresponding experimental one. Evidently, the hydration occurs on the OH, BF3 and C=O groups.