Theoretical Study Of Lp···π/Halogen Bond Competition In Complexes Of Perhalogenated Alkenes With Oxygen/Nitrogen Containing Simple Molecules

In this paper,the possible noncovalent lone pair-π/halogen bond（lp···π/HaB）complexes of perhalogenated unsaturated C₂Cl_nF_4-n（n = 0-4）molecules with five simple molecules containing oxygen or nitrogen as electron donor,water（H₂O）,formaldehyde（H₂CO）,and dimethyl ether（DME）,NH₃ and trimethylamine（TMA）,have been systematically examined by the M06-2X/aug-cc-pVTZ level of theory.Natural bond orbital（NBO）analysis at the same level is used for understanding the electron density distributions of these complexes.The progressive introduction of Cl atom on the C₂Cl_nF_4-n influences more on the lp···π complexes over the corresponding HaB ones.Within the scope of this study,gem-C₂Cl₂F₂ is the best partner molecule for lp···π interaction with the simple molecules,coupled with the greatest interaction energy（IE）,second-order orbital interaction [E（2）] and QCT value,whereas C₂F₄ is the poor partner.The C₂Cl₃F·H₂CO and C₂Cl₄·H₂CO complexes exhibit reverse lp···π bonding,while the Z-C₂Cl₂F₂·H₂O/NH₃,E-C₂Cl₂F₂·H₂O/NH₃,C₂Cl₃F·H₂O/NH₃ and C₂Cl₄·H₂O/NH₃ perform half-lp···π bonding according to the NBO analysis.The lp···π interaction involving the oxygen/nitrogen and the π-hole of the C₂Cl_nF_4-n overwhelms the HaB involving the oxygen/nitrogen and the σ-hole of the Cl atoms in this study.The electron-donation methyl groups contribute significantly for the two competitive interactions,therefore DME and TMA engage stronger in the partner molecules than H₂ O,H₂CO and NH₃.Our theoretical study would be useful for future experimental investigation on noncovalent complexes.