Spectroscopic studies on the potassium 1-fluorobenzoyltrifluoroborate salt by using the FT-IR, Raman and UV–Visible spectra and DFT calculations

Abstract

Potassium 1-fluorobenzoyltrifluoroborate (FBTFB) salt was characterized using Fourier Transformed Infrared (FT-IR) and Raman solid-state spectroscopies as well as ultraviolet–visible spectroscopy in aqueous solution. The functional hybrid B3LYP with the 6-311++G** basis set have optimized the structures of salt in gas phase and in aqueous solution with CS symmetries. In solution, the influence of solvent was studied at the same level of theory with the integral equation formalism variant polarised continuum method (IEFPCM) and the universal solvation model. FBTFB has evidenced the lower solvation energy (−81.54 kJ/mol), as compared with other trifluoroborate salts probably due to the presence of F in the 1st position of phenyl ring that decreases the solubility of this salt. NBO studies clearly support the ionic characteristics of K+F− and K+O− bonds and the high energy values of LPF17→ LP*B14 transitions (ΔΕn→n*) while AIM analyses suggest a high stability of salt in both media due to three ionic and one C–H⋅⋅⋅F interactions. Analyses of frontier orbitals have suggested that the FBTFB salt is more reactive in solution than in gas phase and, than 2-phenylacetyl-trifluoroborate (PTFB) in the two media possibly because FBTFB presents higher global electrophilicity (ω) and nucleophilicity indexes (E) in both media than PTFB. Here, the calculated harmonic force fields, scaled force constants and complete assignments of all vibration normal modes expected for FBTFB in both media are reported. Predicted IR, Raman and UV–Visible spectra have shown good concordance when they are compared with the corresponding experimental ones.