Is There a Single Ideal Parameter for Halogen‐Bonding‐Based Lewis Acidity?

Halogen‐bond donors (halogen‐based Lewis acids) have now found various applications in diverse fields of chemistry. The goal of this study was to identify a parameter obtainable from a single DFT calculation that reliably describes halogen‐bonding strength (Lewis acidity). First, several DFT methods were benchmarked against the CCSD(T) CBS binding data of complexes of 17 carbon‐based halogen‐bond donors with chloride and ammonia as representative Lewis bases, which revealed M05‐2X with a partially augmented def2‐TZVP(D) basis set as the best model chemistry. The best single parameter to predict halogen‐bonding strengths was the static σ‐hole depth, but it still provided inaccurate predictions for a series of compounds. Thus, a more reliable parameter, Ω (σ*), has been developed through the linear combination of the σ‐hole depth and the σ*(C−I) energy, which was further validated against neutral, cationic, halogen‐ and nitrogen‐based halogen‐bond donors with very good performance.