Theoretical study of the interaction in HCCH...X– (X = F, Cl, Br, I) hydrogen-bonded anion–molecule complexes and calculation of the complex formation energy within an electrostatic model

An electrostatic model is proposed to calculate the formation energy ΔЕ of linear HCCH…Х– (X = F, Cl, Br, I) hydrogen-bonded anionic complexes between a halide ion and an acetylene molecule. The potential energy surface (PES) in this model includes four kinds of interaction in the HCCH…Х– system, namely, electrostatic (Coulombic), polarization, dispersive, and exchange repulsion interactions. An analytical expression for the formation energy ΔЕ of the complexes is obtained, and the PES parameters necessary for calculating ΔЕ are determined. The calculated ΔЕ values are in good agreement with ab initio data from the literature. The relative contributions from the different types of interactions to ΔЕ are estimated and analyzed. The electrostatic (Coulombic) interaction makes the main contribution to the formation energy of HCCH…Х– clusters.