2023

Ward, Jas S.; Truong, Khai-Nghi; Erdélyi, Mate; Rissanen, Kari

Halogen bonding occurs between a positive region of a polarized halogen (X), most commonly with an iodine or bromine atom. The polarization, caused by an electron withdrawing group (R), induces electron deficiency onto the halogen atom, creating an electropositive region known as a σ-hole. This σ-hole then interacts with electron-rich nucleophiles (such as Lewis bases, B) forming a linear R–X···B halogen bond. When an electron is completely removed from a halogen, a halogen (I) ion (X+) is formed. A halogen(I) ion itself is highly reactive, but can be ‘trapped’ in between two Lewis bases creating a [L–X–L]+ 3-center, 4-electron halogen bond between the halogen(I) ion and two donor atoms of the Lewis bases (typically nitrogen). Halogen(I) complexes form a special family manifesting a strong halogen bond, which demonstrate good stability in both the solution and solid-states. An overview of the current state of halogen bonding of halogen(I) ion complexes is included, as well as the many advancements made to those fields in recent years.