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Abstract: MP2/6-31++G(d,p) ab initio calculations have been performed to estimate the effect of the H-bond on the vibrational properties of HF due to its complexation with aromatic azines (C n N6-n H n , with n =5, 4 or 3). Our calculations have revealed that the greater is the number of nitrogen atoms in the aromatic ring, the smaller will be the HF stretching frequency downward shift and the increase of the H–F stretching intensity due to complexation. For example, the H–F frequency downward shift is 899cm−1 in pyridine-HF, whereas its corresponding value is 597cm−1 in 1,3,5-triazine-HF. Their infrared intensity ratios between the complexes and their corresponding monomers are 18.7 and 14.3cm−1, respectively. We have found a relationship between the HF stretching frequency downward shift and the number and position of the nitrogen atoms in the aromatic ring. As expected, the HF stretching intensity is enormously increased upon complexation and its value can be predicted by using the ∂P z /∂z H element of the hydrogen polar tensor, where z is the Cartesian axis along the H–F chemical bond. [Copyright &y& Elsevier]

The present manuscript reports a systematic investigation of the basis set dependence of some properties of hydrogen-bonded (π type) complexes formed by propyne and a HX molecule, where X=F, Cl and CN. The calculations have been performed at Hartree–Fock, MP2 and B3LYP levels. Geometries, H-bond energies and vibrational have been considered. The more pronounced effects on the structural parameters of the isolated molecules, as a result of complexation, are verified on RC≡C and HX bond lengths. As compared to double-ζ (6-31G**), triple-ζ (6-311G**) basis set leads to an increase of R C≡C bond distance, at all three computational levels. In the case where diffuse functions are added to both hydrogen and ‘heavy’ atoms, the effect is more pronounced. The propyne–HX structural parameters are quite similar to the corresponding parameters of acetylene–HX complexes, at all levels. The largest difference is obtained for hydrogen bond distance, R H, with a smaller value for propyne–HX complex, indicating a stronger bond. Concerning the electronic properties, the results yield the following ordering for H-bond energies, ΔE: propyne⋯HF>propyne⋯HCl>propyne⋯HCN. It is also important to point out that the inclusion of BSSE and zero-point energies (ZPE) corrections cause significant changes on ΔE. The smaller effect of ZPE is obtained for propyne⋯HCN at HF/6-311++G** level, while the greatest difference is obtained at MP2/6-31G** level for propyne⋯HF system. Concerning the IR vibrational it was obtained that larger shift can be associated with stronger hydrogen bonds. The more pronounced effect on the normal modes of the isolated molecule after the complexation is obtained for H–X stretching frequency, which is shifted downward. [Copyright &y& Elsevier]