Theoretical calculations of the substituent effect on molecular properties of the RCN⋯HF hydrogen-bonded complexes with R=NH2, CH3O, CH3, OH, SH, H, Cl, F, CF3, CN and NO2 (original) (raw)

2009, Vibrational Spectroscopy

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-CBBNÁ Á ÁH-F H-bonded complexes with R = NH 2 , CH 3 O, CH 3 , OH, SH, H, Cl, F, CF 3 , CN and NO 2 . As expected, it has been verified as a red-shift of the H-F stretching frequency (n H-F ), in conformity with the elongation of the bond after complexation. On the other hand, the CBBN stretching frequency (n CB BN ) is blue-shifted and corresponds to a shortening of the bond. The binding energies (DE 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-CBBN molecule (m RCN ) has been found. This result suggests that m 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. ß