CONTENTS 1. Introduction to Halogen Bonding 7119 1.1. Nature of the Halogen Bond 7119 1.2. Scope of the Review 7120 2. Computational and Theoretical Investigations of Halogen Bonding 7120 2.1.Quantum Mechanics Methods 7120 2.2. σ-Hole Model of Halogen Bonding 7120 2.3. Other Contributions to the Nature of Halogen Bonding 7122 2.4. Recent Examples of Computationally Investigated Halogen-Bonded Complexes 7123 2.4.1. XB to Neutral Species 7123 2.4.2. XB to Anions 7126 2.4.3. XB in Protein−Ligand Complexes 7127 2.4.4. Electron-Transfer Processes Affected by XB Interactions 7127 2.5. Classical Force Field Calculations 7127 2.6. Conclusions and Outlook 7129 3. Gas-Phase Studies of Halogen-Bonding Interactions 7130 4. Halogen Bonding in the Solid State 7131 4.1. Introduction to Crystal Engineering and Functional Materials 7131 4.2. Fundamentals 7132 4.3. Halogen-Bonding Hierarchy 7134 4.3.1. Ranking Halogen-Bond Donors 7134 4.3.2. HB/XB Complementarity/Competition 7136 4.3.3. Predicting XBs 7138 4.4. Control of Solid-State Supramolecular Architectures 7138 4.4.1. Polymorphism 7138 4.4.2. Stoichiometry 7139 4.4.3. Tautomeric Control 7140 4.4.4. XBs Involving Metals and Metal-Bound XBs 7140 4.4.5. XB with Anions in the Solid State 4.5. Solid-State Architectures 4.6.

The synthesis of the first halogen bonding [3]rotaxane host system containing a bis‐iodo triazolium‐bis‐naphthalene diimide four station axle component is reported. Proton NMR anion binding titration experiments revealed the halogen bonding rotaxane is selective for nitrate over the more basic acetate, hydrogen carbonate and dihydrogen phosphate oxoanions and chloride, and exhibits enhanced recognition of anions relative to a hydrogen bonding analogue. This elaborate interlocked anion receptor functions via a novel dynamic pincer mechanism where upon nitrate anion binding, both macrocycles shuttle from the naphthalene diimide stations at the periphery of the axle to the central halogen bonding iodo‐triazolium station anion recognition sites to form a unique 1:1 stoichiometric nitrate anion–rotaxane sandwich complex. Molecular dynamics simulations carried out on the nitrate and chloride halogen bonding [3]rotaxane complexes corroborate the 1H NMR anion binding results.

A novel dynamic [3]catenane consisting of a large four-station central macrocycle which incorporates a bay tetrachloro-functionalized perylene diimide (PDI) unit and two triazolium anion-binding motifs, mechanically bonded with two smaller isophthalamide-containing macrocycles, is constructed using an anion template synthetic methodology. Proton NMR, electronic absorption, and fluorescence emission spectroscopies together with molecular dynamics simulations are used to investigate the anion recognition- and solvent-dependent dynamic properties of the higher-order mechanically interlocked molecule. Importantly, unprecedented solvent-dependent and anion-binding-induced circumrotatory motion in a hetero[3]catenane system is demonstrated where the exotic dual rotary switching behavior provides a unique and sophisticated mechanism for optical anion sensing in competitive protic organic and aqueous-organic media.

Two bistable halogen and hydrogen bonding-naphthalene diimide [2]rotaxanes have been prepared and the system incorporating a halogen bond donor anion recognition site is demonstrated to exhibit superior anion induced translational motion of the macrocyclic wheel component relative to the hydrogen bonding analogue.