Theoretical Investigation on Intermolecular Interactions Between HCCF and HCCR(R=F, Cl, Br)

Geometries, interaction energies and electronic properties for four types or dimers(hydrogen bonded, halogen bonded, pi-halogen bonded, and pi-hydrogen bonded) between HCCF and HCCR(R=F, Cl, Br) were studied via MP2/6-311++G(dp) ab initio calculation. It is shown that the strength of the pi-hydrogen bonded dimers turns out to be greater than those of the other three types of dimers, with the interaction energies -4.611 kJ/mol for HCCF-HCCF, -4.700 kJ/mol for HCCF-HCCCl, and -4.850 kJ/mol for HCCF-HCCBr respectively at the CCSD(T)/6-311++ G(d,p)//MP2/6-311++G(dp) level. In an effort to understand the nature of the intermolecular interactions prevalent in these dimers, the interaction energies were decomposed into physically distinct energy' components with the aid of the symmetry adapted perturbation theory(SAPT). The dispersion force is found to be the main origin of the intermolecular interactions in hydrogen bonded and halogen bonded dimers. In the pi-halogen bonded system, the dispersion is the major bonding force in HCCF-HCCF and HCCF-HCCCl,. while the induction energy is the most important component in HCCF-HCCBr. However, both the dispersion and electrostatic energy play a key role in pi-hydrogen bonded dimers.