Quantum chemical investigation of linear hydrogen bonding in ONCCN···HX (X = F,Cl, Br) dimers

Linear hydrogen bonding formed between the nitrogen end of cyanogen‐N‐oxide (ONCCN) and hydrogen halides HX (X = F, Cl, Br) has been observed in their ground Σ states. The order of agreement of energetic stabilities between the correlated functionals used in this calculation is: B3LYP < PBE0 < PBE < PW91 in conjunction with the 6–311++G(3df,3pd) basis set. Analysis of various parameters describing the existence of H‐bonds in these dimers follows the conventional trend: ONCCN···HF > ONCCN···HCl > ONCCN···HBr in the series, except H‐bond lengths and static dipole polarizabilities which are in reverse order. The atomic charges obtained from the Mulliken and natural population analysis is used to assess the charge transfer effects that accompany the dimer formation. It is found from the investigation that the dimers having highest binding energy are accompanied by the highest transfer of charge. The ¹⁴N nuclear quadrupole coupling constants of the monomer ON¹CCN² are found to be decreased upon complection and in the series it increases from F through Br. We observed enhancements in the values of the dimer dipole moment and intrinsic dipole polarizabilities compared with the sum of the monomer values by intermolecular electrical interaction. Investigation reveals vibrational spectral shifts of HX and CN stretching modes similar to the conventional red‐shifted H‐bonded dimers; for the former case, the infrared band intensity increases significantly. Finally, the new vibrational modes originated from the intermolecular interaction are outlined. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007