On the opposite trends of correlations between interaction energies and electrostatic potentials of chlorinated and methylated amine complexes stabilized by halogen bond

The halogen-bonded complexes between F3CCl and ammonia and their methylated and chlorinated derivatives are investigated by ab initio CCSD(T) and density functional BLYP-D3 methods. The interaction energies (ΔE) calculated at the CCSD(T)/cc-pVTZ level range between – 0.90 and – 2.57 kcal mol−1. In all the complexes studied, the AIM analysis has revealed the presence of only one attractive interaction (halogen bond). In the investigated chloramine complexes, an increasing number of the chlorine substituents leads to a decrease in the ΔE, while the opposite effect is observed for the methylated amine complexes, namely the ΔE increases with the increasing number of the methyl groups on N atom. These energies are related to the most negative values on the electrostatic potential surfaces (Vs,min) of the ammonia derivatives. In the case of the chlorinated amine complexes, the positive correlation between the ΔE and Vs,min is observed. On the contrary, the negative correlation between these values is noted for the methylated amine complexes. The NBO results indicate that upon complexation with F3CCl the charge transfer (CT) from the lone pair on N [LP(N)] to the σ*(CCl) orbital decreases with the number of the chlorine substituents, while it increases with the number of the methyl groups on the N atom. It is suggested that the increase in CT in the methylated amine complexes is associated with the weakening of negative hyperconjugation between LP(N) and trans antibonding σ*(CH) orbital(s). This effect is probably responsible for the negative correlation between ΔE and Vs,min in the methylated amine complexes.