Ab initio studies on hydrogen-bonded complexes involving hydrogen cyanide and cyanoacetylene

Abstract

Ab initio calculations using the 4-31G and STO-3G basis sets have been performed to estimate the hydrogen-bond energies and distances of the HCN...HCN, HC3N...HCN, HCN...HC3N, and HC3N...Cchemically bondHC3N complexes. These calculations indicate that both are determined essentially by the nature of the proton donor molecule (PD). An accentuated increase of polarity has been found on each complex due to the H-bond formation. The perturbation of the N...H interaction on the infrared intensity parameters of these atoms has been analyzed from their atomic polar tensors (APTs) using the charge-charge flux-overlap (CCFO) model. This analysis indicates that the P/sub xx//sup (Nb)/ and P/sub xx//sup (Hb)/ elements associated with the deformation modes are practically unaltered due to the formation of the H bond. On the other hand, the P/sub zz//sup Nb)/ and P/sub zz//sup (Hb)/ elements associated with the C identical with N/sub b/ and H/sub b/-C stretching modes are increased by a factor of approx. 2. This increase is principally due to the charge flux term. Their results also show that approximately half the increase in the charge flux term P/sub zz//sup (Hb)/(CF) comes from the charge transfer, whereas the other half comes from the polarization contribution. However, the major contribution tomore » the P/sub zz//sup (Nb)/(CF) term comes from the polarization contribution.« less