Halogen bonds enhanced by σ-hole and π-hole interactions: a comparative study on cooperativity and competition effects between X∙∙∙N and S∙∙∙N interactions in H3N∙∙∙XCN∙∙∙SF2 and H 3N∙∙∙XCN∙∙∙SO2 complexes (X = F, Cl, Br and I).

Halogen bonding, a noncovalent interaction between a halogen atom X in one molecule and a negative site in another, plays an important role in fields as diverse as molecular biology, drug design, and crystal engineering. In this work, the H3N∙∙∙XCN∙∙∙SF2 and H3N∙∙∙XCN∙∙∙SO2 (X = F, Cl, Br, I) complexes are theoretically investigated to find ways to enhance the halogen bond interaction. Cooperative effects are found when X∙∙∙N and S∙∙∙N bonds coexist in the same complex. The ab initio calculations are carried out using at the MP2/aug-cc-pVTZ level, through analysis of surface electrostatic potentials VS(r), interaction energies and the topological analysis based on the quantum theory of atoms in molecules. Particular attention is paid to understand the origin of the X∙∙∙N and S∙∙∙N interactions in the ternary complexes. The cooperativity between both types of the interaction is mainly caused by the electrostatic effects.

Characterization of halogen···halogen interactions in crystalline dihalomethane compounds (CH2Cl2, CH2Br2 and CH2I2): a theoretical study.

A theoretical study was performed to examine halogen···halogen (X···X) bonds properties in crystalline dihalomethane CH2X2 compounds (X=Cl, Br and I). MP2/aug-cc-pVTZ calculations reveal that the interaction energies for CH2X2 dimers lie in the range between -3.7 and -9.9 kJ mol(-1). One of the most important results of this study is that, according to symmetry-adapted perturbation theory, the X···X interactions are largely dependent on dispersion interactions. The contribution of electrostatic energy in the X···X interaction increases in the order Cl < Br < I, which is consistent with the greater amount of positive electrostatic potential on the halogen atom.

Theoretical study of the complementarity in halogen-bonded complexes involving nitrogen and halogen as negative sites.

This article analyzes the interplay between X···N and X···X halogen bonds interactions in NCX···NCX···XCH3 complexes, where X=Cl and Br. To better understand the properties of these systems, the corresponding dyads were also studied. These effects are studied theoretically in terms of geometric and energetic features of the complexes, which are computed by ab initio methods. The estimated values of cooperative energy (E coop) are all negative with much larger E coop in absolute value for the NCBr···NCBr···BrCH3 system. The effect of X···N on the properties of X···X is larger than that of X···X bonding on the properties of X···N. These results can be understood in terms of the electrostatic potentials of the negative sites with which the positive regions on the halogens are interacting. The nature of halogen bond interactions of the complexes is analyzed using parameters derived from the energy decomposition analysis.