Comparison of halogen with proton transfer. Symmetric and asymmetric systems

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

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.

Promotion of TH3 (T = Si and Ge) group transfer within a tetrel bond by a cation-π interaction

The possibility of the transfer of the TH₃ group across a tetrel bond is considered by ab initio calculations. The TB is constructed by pairing PhTH₃ (Ph = phenyl; T = Si and Ge) with bases NH₃, NHCH₂, and the C₃N₂H₄ carbene. The TH₃ moves toward the base but only by a small amount in these dimers. However, when a Be²⁺ or Mg²⁺ dication is placed above the phenyl ring, the tetrel bond strength is greatly magnified reaching up to nearly 100 kcal mol^-1. This dication also induces a much higher degree of transfer which can be best categorized as half-transfer for the two N-bases and a near complete transfer for the carbene.

Search for an exothermic halogen bond between anions

A halogen-bonded complex containing a pair of anions can be made more stable than the isolated anions if the Lewis acid is a long carbon chain, fully substituted by CN groups, with an I atom on one end and a COO− group on the other, with Cl− as base.