Enhancing effects of electron-withdrawing groups and metallic ions on halogen bonding in the YC6F4X···C2H8N2 (X = Cl, Br, I; Y = F, CN, NO2, LiNC+, NaNC+) complex.

Halogen-bonding interactions are highly directional intermolecular interactions that are often important in crystal engineering. In this work, the second-order Møller-Plesset perturbation theory (MP2) calculations and the quantum theory of "atoms in molecules" (QTAIM) and noncovalent interaction (NCI) studies were carried out on a series of X···N halogen bonds between substituted haloperfluoroarenes C6F4XY (X = Cl, Br, I; Y = F, CN, NO2) as bond donors and 1,2-diaminoethane as bond acceptor. Our research supports earlier work that electron-withdrawing substituents produce an enhancement effect on the size of the σ-hole and the maximum positive electrostatic potentials (VS,max), which further strengthens the halogen bonding. The metallic ion M(+) (M(+) = Li(+), Na(+)) has the ability to enhance the size of both the σ-hole and VS,max value with the formation of [MNCC6F4X](+), resulting in more electronic charge transfer away from the halogen atom X and an increase in the strength of the halogen bond. It is found that the values of V(S,max) at the σ-holes are linear in relation to the halogen-bonded interaction energies and the halogen-bonding interaction distance, indicating that the electrostatic interaction plays a key role in the halogen-bonding interactions. The values of V(S,max) at the σ-holes are also linear in relation to the electron density ρ(b), its Laplacian nabla(2)ρb, and -Gb/Vb of XB, indicating that the topological properties (ρb, nabla(2)ρb) and energy properties (Gb, Vb) at the BCPs are correlated with the electrostatic potentials.