CCSD(T) level interaction energy for halogen bond between pyridine and substituted iodobenzenes: origin and additivity of substituent effects

Abstract

The CCSD(T) level interaction energies at the basis set limit (E_int) were calculated for 33 halogen bonded pyridine complexes with substituted iodobenzenes. The CCSD(T) level electron correlation correction substantially decreases the magnitude of attraction in comparison with the MP2. The E_int for the pyridine complexes with mono substituted iodobenzenes varies from −3.14 to −4.42 kcal mol⁻¹, depending on the substituent. The electron-withdrawing substituents such as NO₂ enhance the attraction, while the effects of electron-donating substituents reduce. The additivity of the substituent effects is observed for the E_int of the pyridine complexes with multiple substituted iodobenzenes. The electrostatic interactions are mainly responsible for the substituent effects on the magnitude of the attraction in the halogen-bonded complexes. The electrostatic energy depends significantly on the substituent. They have a strong correlation with the E_int. On the other hand the effects of the substituent on the dispersion energy are small, however the dispersion does contribute greatly to the attraction.