Theoretical investigations on the enhancing effect of the cation-π interaction on the halogen bond in the M•••HCCX•••NH3 (M=Li+, Na+, Cu+, Ag+, Au+; X=Cl, Br) complexes

The M center dot center dot center dot HCCX center dot center dot center dot NH3 (M=Li+, Na+, Cu+, Ag+, Au+; X=Cl, Br) complexes were designed to study the influence of cation-pi interaction on the X center dot center dot center dot N halogen bonds under M05-2X/aug-cc-pVDZ(PP) level. In comparison with the HCCX center dot center dot center dot NH3 complexes, the bond distances of the halogen bonds have decreased, and the interaction energies become more negative. The results show that the X center dot center dot center dot N halogen bonds have been strengthened by the cation-pi interactions. For different cations, the enhancing effect is more intensive in the order of Au+ > Cu+ > Ag+ > Li+ > Na+, which indicates that transition metal cations can enhance the halogen bond in a stronger manner. Molecular electrostatic potential and second-order perturbation stabilization energy were calculated to deepen the discussion. In addition, atoms in molecules analysis was performed and the electron density shift was studied.