P … π Bonds in Complexes of C2H2 … PH2X (X = H, F, Cl, Br, I): Quantum Chemical Analysis

Abstract

Non-covalent bonds take a strong in numerous chemical and biological phenomena, bringing them to the forefront of research. We studied the structure and interaction properties of C2H2 and PH2X using quantum chemistry following the Moller-Plesset method (MP2). The results showed that C2H2 and PH2X could form a stable complex (C2H2 … PH2X (X= H, F, Cl, Br, I)) of Cs symmetry. The halogen X was far away from the C2H2 molecule, and the P atom was not directly above the center of the C≡C bond. The molecular interaction energy of C2H2 … PH2X varied between -6.3 and -14.5 kJ/mol. This revealed the generation of a long-range weak interaction. Analysis of the interaction energy revealed that the substitution of halogen atoms promoted the formation of the complex (C2H2 … PH2X). The interaction energy of the complex decreased in the order F>Cl>Br>I, which was consistent with the change in electronegativity of the halogen atoms. Independent Gradient Model (IGM) analysis calculations showed that van der Waals interaction was the dominant weak interaction in C2H2 … PH2X. The symmetry-adapted perturbation theory (SAPT) was used to study the system, and the results revealed that the interactions in C2H2 … PH3, C2H2 … PH2I were primarily dispersive, and the interactions in C2H2 … PH2F, C2H2 … PH2Cl, C2H2 … PH2Br were primarily electrostatic.