Ab Initio Investigation of Interactions Between Dihalogens and NCH Lewis Base

This study employs ab initio calculations (MP2/aug-cc-pVDZ) to investigate the properties, structures, and interaction dynamics of dihalogens (F₂, Cl₂, Br₂, FCl, FBr, ClBr) as Lewis acids interacting with NCH as a Lewis base. Electrostatic potential (ESP) analysis was conducted to identify σ-holes on the dihalogen systems. ESP analysis confirmed the presence of σ-holes on the dihalogens, with the following order of increasing magnitude: FBr > FCl > ClBr > Br₂ > Cl₂ > F₂. Interaction energies revealed that the FBr···NCH complex exhibited the strongest interaction, indicating its potential as a robust Lewis acid. NBO analysis demonstrated charge transfer from NCH to the dihalogen atoms, supporting the presence of significant noncovalent interactions. The wiberg bond index (WBI) values ranged from 0.00 to 0.10, reinforcing the noncovalent nature of the interactions. Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) index analyses were applied to elucidate the nature and origin of the interactions. These analyses confirmed a closed-shell character, indicating attractive forces within the studied complexes.