Directionality of Halogen Bonds: An Interacting Quantum Atoms (IQA) and Relative Energy Gradient (REG) Study

Abstract

Interacting Quantum Atoms (IQA) and Interacting Quantum Fragments (IQF) analyses are used to study normalF3C-X⋯NnormalH3 (X=Cl and Br) model complexes in order to determine the origin of halogen bond directionality. IQA allows for the calculation of intra‐ and interatomic classical and exchange‐correlation energies, which can be used to determine the energetic nature of the changes that occur when deviating from the preferred halogen bond approach. The Relative Energy Gradient (REG) method is also applied to rank the IQA energies and reveal which energy contributions best describe the total behavior of the system. Indeed, all the pairwise interactions and atomic self‐energies are angularly dependent; some terms favor the linear structure and some tend toward nonlinear arrangements. For instance, when the C−X−N angle is altered, the halogen‐nitrogen interaction energy behaves like the total energy of the system while the carbon‐nitrogen interaction works against the total energy profile. Furthermore, the REG values reveal that the contribution of the halogen‐nitrogen interaction to the total behavior of the system is small. Instead, the secondary interactions (e. g., fluorine‐nitrogen and carbon‐hydrogen interactions) and atomic self‐energies are mainly responsible for the angular preference of these halogen bonds. Finally, IQF calculations followed by REG analysis reveal the importance of the self‐energy of the fragments.

Fluorine as a Lewis acid: A symmetry‐adapted perturbation theory based on density functional theory and interacting quantum atoms study of noncovalent interactions in the NCF⋯NH3 complex

“…Indeed, the trends in the angular dependence of the interatomic interactions are similar to those of the halogen bonds of our previous study. [ 28 ] In particular, our results show that the exchange‐correlation components of interatomic interactions are almost angularly independent, while the electrostatic parts vary with the angular distortions. This picture complies with the MEP maps of NCCl and NCBr molecules (Figure 3), and highlights the importance of electrostatic interactions in the directionality of halogen bonds.…”

“…Moreover, Based on the natural energy decomposition analysis (NEDA), [ 24–27 ] it is shown by Huber et al [ 19 ] that the linearity of F 3 C  I⋯NH 3 halogen bonded complex is mostly owing to the sum of charge transfer and Pauli repulsion terms, while the electrical component favors the nonlinear C  I  N arrangement. Besides, in a recent work, [ 28 ] we used interacting quantum atoms (IQA) [ 29–31 ] approach to determine the origins of the directionality in the halogen bonds, which resulted in the idea that although the total electrostatic interaction between the fragments is almost angularly independent, the individual interatomic electrostatic interactions play significant roles.…”

New insights in chemical reactivity from quantum chemical topology

“…It has long been well‐known that the electrostatic contribution, here termed , accounts for a large fraction of the interaction energy in most intermolecular interactions even though other contributions are not necessary small or very small 79–83 . In the context of this work, it is interesting to quantify the role and the magnitude of the terms involved in Equation ().…”

Challenging the electrostatic σ‐hole picture of halogen bonding using minimal models and the interacting quantum atoms approach

“…22,25,[28][29][30][31][32][33] On the other hand, the IQA picture has also revealed how in some instances covalent effects, as revealed by non-negligible exchange-correlation energies, may have been skipped. 32,[36][37][38][39][40][41][42][43][44] In this work, we have decided to adhere to Occam's razor argu- [1894] p.483a) and thus to choose the simplest possible model systems of halogen bonding in order to isolate as well as possible the driving forces behind their stability through the IQA partitioning. Since XBs comprise a σ-hole bearing halogen atom acting as a Lewis acid that interacts with a Lewis base counterpart, we opted to explore the σ-hole halogen interactions within negatively charged X 1 − Y 2 − X 3 species, using different combinations of chlorine, bromine and iodine as the X and Y moieties.…”