Characteristics and nature of halogen bonds in linear clusters of NCX (X=Cl, and Br): an ab initio, NBO and QTAIM study

Abstract

A theoretical study was performed to examine intermolecular halogen bond properties in one-dimensional NCX chains (X=Cl and Br). Geometries, binding energies, and charge-transfer of linear (NCCl)_2–10 and (NCBr)_2–10 chains were investigated by means of second-order Møller–Plesset perturbation theory (MP2) and DFT methods. All MP2, B3LYP and M06/aug-cc-pVTZ results indicate that the magnitudes of the interaction energies increase with increasing halogen size. Considering MP2/aug-cc-pVTZ results, it can be seen that the (NCBr)₁₀ cluster is bound −12.72 kcal/mol more strongly than (NCCl)₁₀. The n-dependent trend of charge-transfer is reasonably correlated with cooperative effects in halogen bond energies. According to the quantum theory of atoms in molecules, the capability of the (NCX)_2–10 clusters for electron localization, at the C–X ··· N bond critical point (BCPs), depends on the cluster size and thereby leads to cooperative changes in the C–X ··· N strength, and charge-transfer. It is also revealed that for all intermolecular C–X ··· N interactions, total electronic energy densities are all greater than zero, suggesting that the interactions are significantly electrostatic in nature.

Keywords:

• halogen bond
• QTAIM
• NBO
• cooperative effects
• EDA