Evaluating structures, properties and vibrational and electronic spectra of the potassium 2-isonicotinoyltrifluoroborate salt

Abstract

The potassium 2-isonicotinoyltrifluorborate salt has been characterized by using FT-IR, FT-Raman and UV–Visible spectroscopies while its structural properties were studied by using B3LYP/6-31G* and B3LYP/6-311++G** calculations in gas and aqueous solution phases. Four conformers with CS and C1 symmetries were found in the potential energy surfaces but only one of them presents the minimum energy. Two dimeric species of this salt were also optimized in accordance to the layered architectures suggested for trifluoroborate potassium salts in the solid phase. Here, the experimental Raman bands at 796, 748 and 676 cm−1 clearly support the presence of both dimers. On the other hand, the 2-isonicotinoyltrifluorborate anion was optimized because its presence is expected in solution. Reasonable correlations were observed between the predicted FTIR, Raman and UV–visible spectra with the corresponding experimental ones. The solvation energies for the salt in aqueous solution were predicted by using both methods. Here, it is observed that the change of furane by pyridine ring generates an increase in the solvation energies of the potassium 2-isonicotinoyltrifluorborate salt in relation to potassium 3-furoyltrifluoroborate salt. The study of the charges has revealed that there is an effect of the size of the basis set on the Mulliken charges while the AIM analyses suggest that the F⋯H and O⋯K interactions are also strongly dependent of the medium and the size of the basis sets. The bond orders for the F and K atoms evidence their higher ionic characteristics in solution with both basis sets. The NBO and AIM results clearly support the higher stability of this salt in both media. The studies by using the frontier orbitals indicate that the change of furane by pyridine ring decreases the reactivity of this salt by using 6-31G* basis set but increases when the other one is employed. Another effect of change of furane by pyridine ring is observed in the increase of the f(νCO) and f(νBF3) force constants. In addition, the force fields for the salt in both media were reported together to their complete vibrational assignments and force constants by using both levels of theory.