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

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 C 2 H 2 and PH 2 X using quantum chemistry following the Moller-Plesset method (MP2). The results showed that C 2 H 2 and PH 2 X could form a stable complex (C 2 H 2 … PH 2 X (X= H, F, Cl, Br, I)) of Cs symmetry. The halogen X was far away from the C 2 H 2 molecule, and the P atom was not directly above the center of the C≡C bond. The molecular interaction energy of C 2 H 2 … PH 2 X 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 (C 2 H 2 … PH 2 X). 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 C 2 H 2 … PH 2 X. The symmetry-adapted perturbation theory (SAPT) was used to study the system, and the results revealed that the interactions in C 2 H 2 … PH 3 , C 2 H 2 … PH 2 I were primarily dispersive, and the interactions in C 2 H 2 … PH 2 F, C 2 H 2 … PH 2 Cl, C 2 H 2 … PH 2 Br were primarily electrostatic.