Characterization of potassium (2-phenylacetyl) trifluoroborate salt by using the UV–Visible, FT-IR and FT-Raman spectra

Abstract

The potassium 2-phenylacetyl-trifluoroborate (PTFB) salt has been experimentally characterized by using FT-IR, FT-Raman and ultraviolet–visible spectroscopies while its structures were theoretically determined in gas phase and in aqueous solution by using B3LYP/6–311++G** method. The studies in solution were performed at the same level of theory with the integral equation formalism variant polarised continuum method (IEFPCM) and the universal solvation model. The comparisons among the predicted IR, Raman and UV–Visible spectra have evidenced good concordance with the corresponding experimental ones. PTFB presents a solvation energy of −87.64 kJ/mol, a value lower than the observed for 5-hydroxypentanoyl-trifluoroborate (HTFB) (−103.73 kJ/mol) and 2-isonicotinoyl-trifluoroborate (ITFB) (−95.05 kJ/mol) and higher than 3-furoyl-trifluoroborate (FTFB) (−84.72 kJ/mol). Evidently, the phenyl ring in PTFB decreases the solubility of this salt, as compared with hydroxypentanoyl chain in HTFB, furoyl ring in FTFB and pyridine ring in IFTB. The bond orders studies support the ionic characteristics of K⋯B bonds while the NBO studies reveal a lower stability of PTFB in aqueous solution, as compared with the value in gas phase probably due to the low solvation energy of PTFB in this medium. The four interactions observed for PTFB in gas phase by the AIM analyses support the high stability of PTFB in gas phase. The gap values show that PTFB is most reactive in gas phase than in aqueous solution while the comparisons with other salts containing pyridine ring instead phenyl one reveal that reactivity increase when in the 5 position of pyridine ring is incorporates a Br atom in the structure of salt. Hence, the following reactivity order it is observed in gas phase: Br-ITFB > ITFB > PTFB changing in solution to: ITFB > Br-ITFB > PTFB. In solution, probably the salt is most reactive due to the most negative nucleophilicity index and higher electrophilicity index. The harmonic force fields, force constants and complete assignments of all vibration normal modes for PTFB in both media for first time are reported.