CO2 capture through halogen bonding: A theoretical perspective

Halogen bonding interactions between several halogenated ion pairs and CO₂ molecules have been investigated by means of density functional theory calculations. To account for the influence of solvent environment, the implicit polarized continuum model was also employed. The bromide and iodide cations of ionic liquids (ILs) under study can interact with CO₂ molecules via X??O interactions, which become much stronger in strength than those in the complexes of iodo-perfluorobenzenes, very effective halogen bond donors, with CO₂ molecules. Such interactions, albeit somewhat weaker in strength, are also observed between halogenated ion pairs and CO₂ molecules. Thus, the solubility of CO₂ may be improved when using halogenated ILs, as a result of the formation of X??O halogen bonds. Under solvent effects, the strength of the interactions tends to be weakened to some degree, with a concomitant elongation of intermolecular distances. The results presented here would be very useful in the design and synthesis of novel and potent ILs for CO₂ physical absorption.