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.

Iodotriazole and triazole anion recognition groups have been integrated into a picket-fence zinc(ii)-metalloporphyrin scaffold to produce receptors for anion recognition and sensing applications. (1)H NMR and UV/visible spectroscopic investigations reveal both host systems exhibit strong anion binding affinities in a range of solvent media. Importantly, the halogen-bonding iodotriazole-containing porphyrin-based host displays halide binding affinities substantially larger than the protic-functionalised analogue concomitant with a reduced strength of oxoanion complexation.

A new, versatile chloride-anion-templating synthetic pathway is exploited for the preparation of a series of eight new [2]rotaxane host molecules, including the first sulfonamide interlocked system. (1)H NMR spectroscopic titration investigations demonstrate the rotaxanes' capability to selectively recognise the chloride anion in competitive aqueous solvent media. The interlocked host's halide binding affinity can be further enhanced and tuned through the attachment of electron-withdrawing substituents and by increasing its positive charge. A dicationic rotaxane selectively binds chloride in 35% water, wherein no evidence of oxoanion binding is observed. NMR spectroscopy, X-ray structural analysis and computational molecular dynamics simulations are used to account for rotaxane formation yields, anion binding strengths and selectivity trends.

Getting connected: The formation of pseudorotaxane assemblies between a designed macrocyclic halogen bonding (XB) acceptor (red in scheme) and a series of XB donor threading components was templated by a single halogen bond. The strength of the XB assembly between the pyridine macrocycle and iodopyridinium thread was utilized in the ring‐closing metathesis clipping synthesis of a [2]catenane.

Triazole and triazolium groups have been integrated into a zinc(II) metalloporphyrin-based structural framework to produce two porphyrin-cages for anion sensing applications. UV/visible spectroscopic titration investigations reveal both host systems exhibit strong anion binding affinities, with the positively-charged triazolium-porphyrin cage capable of colorimetric sensing halides, fluoride and chloride, and oxoanions in acetone-water solvent mixtures.