Cooperativity of hydrogen and halogen bond interactions

The cooperativity effects in the Cl- center dot center dot center dot HCCH center dot center dot center dot HF, Cl- center dot center dot center dot ClCCH center dot center dot center dot HF and F- center dot center dot center dot ClCCH center dot center dot center dot HF complexes are analyzed here. The results show that the formation of the hydrogen and halogen bonds is ruled by the same mechanisms and that the cooperativity enhances these interactions. The MP2(full)/6-311 ++G(d,p) calculations were performed for the above triads and the corresponding sub- units; dyads linked by the hydrogen or halogen bonds and monomers. The NEDA scheme of the decomposition of the interaction energy was applied here. It was found that for the halogen bonded systems, the most important is the polarization term of the energy of interaction while for the hydrogen bonds the charge transfer interaction energy and next the electrostatic contribution. The interaction between orbitals is also analyzed here in terms of the Natural Bond Orbitals method.