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

Abstract

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 C 2H 2 2(HF) hydrogen bonded complex, besides the well-known (π⋯H) interaction formed between the hydrofluoric acid and the C C bond of the acetylene, as well as the (F d⋯H e) 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 (F f) of the second HF molecule and the hydrogen atom (H b) of the acetylene, characterizing then a new hydrogen bond, (F f⋯H b). Moreover, the AIM calculations discovered an important aspect relative to the (π⋯H) interaction, which is not linked in the midpoint of the C C bond of the acetylene but formed directly by the interaction between the hydrogen atom (H c) of the first HF molecule and the C 2 atom of the acetylene in the C 2H 2 2(HF) complex. In this sense, the C 2H 2 2(HF) hydrogen bonded complex can be considered an intramolecular system constituted of three hydrogen bonds.