Theoretical calculations of the substituent effect on molecular properties of the R-C≡N···H-F hydrogen-bonded complexes with R= NH2, CH3O, CH3, OH, SH, H, Cl, F, CF3, CN and NO2

摘要

DFT calculations with B3LYP and PBE1PBE functionals and 6-311 ++G(d,p) basis set have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the R-C≡N···H-F H-bonded complexes with R = NH2, CH3O, CH3, OH, SH, H, Cl, F, CF3, CN and NO2. As expected, it has been verified as a red-shift of the H-F stretching frequency (v_(H-F)). in conformity with the elongation of the bond after complexation. On the other hand, the C≡N stretching frequency (v_(C≡N)) is blue-shifted and corresponds to a shortening of the bond. The binding energies (ΔE_c), including BSSE and ZPVE corrections, show a linear correlation with several structural, electronic and vibrational properties. In particular, an important linear dependence between the binding energy and the calculated dipole moment of the free R-C≡N molecule (μ_(RCN)) has been found. This result suggests that μ_(RCN) can be a useful quantity in order to predict the ability of this fragment to form a hydrogen-bond. The IR intensities of stretching and bending modes of complexed H-F acid fragment are adequately interpreted through the atomic polar tensor of the hydrogen atom in H-F using the modified CCFO model for infrared intensities. The new vibrational modes arising from complexation show several interesting features.