The hydrogen bond in the acetylene-2(HF) complex: A theoretical study about intramolecular and unusual π⋯H interactions using DFT and AIM calculations

We present a theoretical study about hydrogen complexes formed by acetylene and hydrofluoric acid using B3LYP/6-311++G(d,p) calculations and topological parameters of the atoms in molecules theory. In the C2H22(HF) hydrogen bonded complex, besides the well-known (π⋯H) interaction formed between the hydrofluoric acid and the CC bond of the acetylene, as well as the (Fd⋯He) hydrogen bond in the 2(HF) dimer within the ternary hydrogen complex, the topological parameters identified a bond critical point proceeding from interaction between the fluoride atom (Ff) of the second HF molecule and the hydrogen atom (Hb) of the acetylene, characterizing then a new hydrogen bond, (Ff⋯Hb). Moreover, the AIM calculations discovered an important aspect relative to the (π⋯H) interaction, which is not linked in the midpoint of the CC bond of the acetylene but formed directly by the interaction between the hydrogen atom (Hc) of the first HF molecule and the C2 atom of the acetylene in the C2H22(HF) complex. In this sense, the C2H22(HF) hydrogen bonded complex can be considered an intramolecular system constituted of three hydrogen bonds.