A theoretical investigation of the competition between σ- and π-holes on the stability of the complexes resulting from the interaction between the COCl2 and OCY molecules (Y = S, Se, and Te)

Carbonyl dichloride (COCl₂), also known as phosgene, is a highly toxic gas, whose exposure or acute inhalation causes severe respiratory complications, such as pulmonary edema, pulmonary emphysema, and even death. In this study, we theoretically investigated the complexes formed by the interaction between the COCl₂ (phosgene) and OCY molecules (Y = S, Se, and Te). Complex geometry optimization yielded three distinct types of conformations. Conformation-I complexes were stabilized by two concurring chalcogen-bonding interactions (i.e. O⋯Y and Cl⋯Y) by forming a ring structure. However, only a single linear interaction (O⋯C) or (O⋯Cl) occurred in conformation-II and III complexes, forming complexes with the nature of tetrel and halogen bonds, respectively. According to the results of the molecular electrostatic potential (MEP), interaction energy (ΔE^T), natural bond orbital (NBO), and so on, the σ-hole of the Y atom in the OCY molecule exhibited higher acidic strength and formed more stable complexes than those resulting from the σ- and π-holes of the COCl₂ molecule.