Halogen Bonding: A Study based on the Electronic Charge Density

Abstract

Density functional theory (DFT) and atoms in molecules theory (AIM) were used to study the characteristic of the noncovalent interactions in complexes formed between Lewis bases (NH(3), H(2)O, and H(2)S) and Lewis acids (ClF, BrF, IF, BrCl, ICl, and IBr). In order to compare halogen and hydrogen bonds interactions, this study included hydrogen complexes formed by some Lewis bases and HF, HCl, and HBr Lewis acids. Ab initio, wave functions were generated at B3LYP/6-311++G(d,p) level with optimized structures at the same level. Criteria based on a topological analysis of the electron density were used in order to characterize the nature of halogen interactions in Lewis complexes. The main purpose of the present work is to provide an answer to the following questions: (a) why can electronegative atoms such as halogens act as bridges between two other electronegative atoms? Can a study based on the electron charge density answer this question? Considering this, we had performed a profound study of halogen complexes in the framework of the AIM theory. A good correlation between the density at the intermolecular bond critical point and the energy interaction was found. We had also explored the concentration and depletion of the charge density, displayed by the Laplacian topology, in the interaction zone and in the X-Y halogen donor bond. From the atomic properties, it was generally observed that the two halogen atoms gain electron population in response to its own intrinsic nature. Because of this fact, both atoms are energetically stabilized.

Electron density Laplacian and halogen bonds

“…This space region is thus prone to interact with the lone electron pair(s) carried by the partner. Recently, a similar analysis (also valid for homologous noncovalent bonds) has been proposed using, as the primary physical observable, the electron density Laplacian ∇ 2 ρ(� r) [25][26][27][28] instead of MEP, leading to the so-called lump-hole interaction paradigm [29]: the electron-deficient region at the periphery of the halogen atom is then viewed as a "hole" that can be filled by the electron-rich Lewis base's lump. Indeed, it is very well known that charge depletion areas are easily characterized by positive ∇ 2 ρ(� r) values, while charge concentration occurs when ∇ 2 ρ(� r) is negative.…”

Magnitude and Origin of the Attraction and Directionality of the Halogen Bonds of the Complexes of C6F5X and C6H5X (X=I, Br, Cl and F) with Pyridine

“…The SAPT calculations of small model complexes of the halogen bond also show that electrostatic interactions are mainly responsible for the attraction. [68,72,73] On the other hand, it has been stressed repeatedly that charge-transfer (orbital-orbital) interactions are an important source of the attraction in halogen bonds. [7,[69][70][71][72][73][74][75][76][77][78][79] The strong correlation between the electron-density transfer and the interaction energy suggests that charge-transfer interactions play important roles in the attraction.…”

Probing the selective separation of potassium ion from sodium ion with cyclopentadienyl anion as receptor: a computational study

“…Furthermore, the Laplacian electron density ∇ 2 ρ(r) is related to the local components, kinetic G(r c ) and potential V(r c ), of the total energy with the expression (in a.u. : (1/4 ∇ 2 ρ(r)=2G(r)+V(r)) [55]. The positive sign of ∇ 2 ρ(r) indicates that the electron density is locally depleted, and the kinetic energy governs over the potential energy [55].…”

“…Stability of these Cp-M complexes in different stoichiometry ratio has been performed in the aqueous phase. The Bader's atoms in molecule (AIM) analysis have been carried out sequentially to achieve the cage critical point which indicates the nature and strength of cation-π interaction [55]. In order to explain the role of various contributing factors to the total interactions energy of the Cp-M complexes, the localized molecular orbital energy decomposition analysis (LMO-EDA) has been performed as implemented in the quantum chemistry software GAMESS [56,57].…”