Substituent and transition metal effects on halogen bonding: CSD search and theoretical study

According to our survey of the Cambridge Structural Database (CSD), a large number of X-ray crystal structures containing C–X⋯NCC/C–X⋯NCM halogen bonds were extracted. In this work, DFT/M06 calculations have been carried out to investigate the influence of substituents and transition metals on halogen bonding. It was found that electron-withdrawing/electron-donating substituents in electron donors slightly weaken/strengthen halogen bonds, while the introduction of transition metals leads to somewhat stronger halogen bonds. On the basis of electrostatic potential (ESP) analysis, these interactions are mainly electrostatic in nature, and moreover electrostatic forces play an important role in the enhancement or attenuation of halogen bonds with the presence of substituents and transition metals in electron donors. In addition, some X-ray crystal structures retrieved from the CSD were selected to provide experimental evidence of these halogen bonds.