The effects of cation-π and anion-π interactions on halogen bonds in the [N⋯X⋯N]⁺ complexes: A comprehensive...

The effects of ion-π interaction on the [N⋯X⋯N]⁺ halogen bond have been investigated by placement of monovalent ions on a pyridine ring plane of the complexes. The structural and electronic properties of the complexes have been studied via the density functional theory (DFT), quantum theory of atoms in molecules (QTAIM), non-covalent interaction (NCI) index and the nuclear magnetic resonance (NMR) calculations. The evaluation of halogen bonds in bis(pyridine)halonium complexes reveals the existence of two factors, ion-π interactions and intermolecular N─N distance, which play the important roles on the formation and stability of these quaternary complexes. The complexes are made via halogen bonding, where anti-cooperativity effect between two halogen bonds can be a reason for the change in quaternary complexes. The cation-π interaction decreases the total binding energy ǀΔEǀ, while anion-π interaction increases that. The trend in the ǀΔEǀ values are Ag⁺ < Au⁺ < Cu⁺ < py₂X⁺ < Br-< Cl- < F- and is not changed by the methods of calculations. The spin-spin coupling constants ^2XJ_N─N increase in the following order ¹⁵N⋯Cl⁺⋯¹⁵N > ¹⁵N⋯Br⁺⋯¹⁵N > ¹⁵N⋯I⁺⋯¹⁵N, as it similarly observes for the ǀΔEǀ and the cooperativity and synergetic energies (E_coop and E_syn). According to AIM and NMR analysis, ¹J_N⋯X and ^1XJ_N⋯X have opposite signs in closed and shared shell XBs. The obtained potential curves can be applied as valuable data to describe the effect of ion-π interaction on the improving of the three-center-four-electron [N⋯X⋯N]⁺ complexes reactivity.