Halogen Bonds of Halogen(I) Ions─Where Are We and Where to Go?

Abstract

Halenium ions, X + , are particularly strong halogen-bond donors that interact with two Lewis bases simultaneously to form linear [D•••X•••D] + -type halonium complexes. Their three-center, four-electron halogen bond is both fundamentally interesting and technologically valuable as it tames the reactivity of halogen(I) ions, opening up new horizons in a variety of fields including synthetic organic and supramolecular chemistry. Understanding this bonding situation enables the development of improved halogen(I) transfer reactions and of advanced functional materials. Following a decade of investigations of basic principles, the range of applications is now rapidly widening. In this Perspective, we assess the status of the field and identify its key advances and the main bottlenecks. Clearing common misunderstandings that may hinder future progress, we aim to inspire and direct future research efforts.

Photoluminescent organic crystals and co-crystals

“…Halogen bonding has been a significant addition to crystal engineers tool-kit and utilized to design materials with novel properties, including thermally expanding, soft and room temperature phosphorescent crystals. 151 Several halogen-bonded emissive co-crystals have been reported and fine-tuning of their emission has been realised through crystal engineering interventions. However, in the majority of systems, the interaction is used as an additional hook to associate the crystal components or acts as a competing associative force during crystallization.…”

Halogen Bond via an Electrophilic π-Hole on Halogen in Molecules: Does It Exist?

“…However, the authors have suggested that crystallographic analysis can reveal close contacts, but calculated electrostatic potentials can provide insight into the extent of variations in positive potentials on the cationic surfaces and negative potentials on the anionic surfaces. Similarly, Wieske and Erdelyi [147] discussed the bonding features of hypervalent halogen (I) complexes. They argued that the halonium ions bound to two carbons, [C-X-C] + , do not possess halogen-bond donor character, as discussed by many research groups in the past.…”