Stabilisation of Bromenium Ions in Macrocyclic Halogen Bond Complexes.

Halenium ions (X) are highly reactive electron deficient species that are prevalent transient intermediates in halogenation reactions. The stabilisation of these species is especially challenging, with the most common approach to sequester reactivity through the formation of bis-pyridine (Py) complexes; [(Py)X]. Herein, we present the first example of a macrocyclic stabilisation effect for halenium species.

Bis-Squaramide-Based [2]Rotaxane Hosts for Anion Recognition.

The first examples of bis-squaramide axle containing [2]rotaxanes linked via rigid aryl and flexible alkyl spacers synthesised using copper(I) catalysed active metal template methodology are reported. The halide and oxoanion binding properties of the [2]rotaxanes in aqueous-organic solvent media are examined through extensive H-NMR titration experiments to investigate the impact of integrating multiple squaramide motifs on the anion binding capabilities of the interlocked receptors. These studies reveal that the bis-squaramide rotaxane host systems exhibit enhanced halide anion binding capabilities relative to a mono-squaramide axle functionalised rotaxane, demonstrating a rare anti-Hofmeister bias halide anion selectivity trend in aqueous-organic mixtures and highlighting the efficacy of the potent solvent shielded hydrophobic interlocked binding pocket created upon mechanical bond formation.

Determining Ion-Pair Binding Affinities of Heteroditopic Receptor Systems.

Determining ion-pair affinities in heteroditopic receptor systems presents a persistent and significant challenge. The plethora of technical and experimental problems implicated in measuring ion-pair affinities have encouraged the use of several expedient experimental practices as a means of characterising ion-pair recognition behaviour. Exploiting a model heteroditopic receptor system, we interrogate the reliability of these methods and demonstrate that these commonly used techniques can be highly questionable and without extreme care can lead to incorrect conclusions.

Selective sodium halide over potassium halide binding and extraction by a heteroditopic halogen bonding [2]catenane.

The synthesis and ion-pair binding properties of a heteroditopic [2]catenane receptor exhibiting highly potent and selective recognition of sodium halide salts are described. The receptor design consists of a bidentate halogen bonding donor motif for anion binding, as well as a di(ethylene glycol)-derived cation binding pocket which dramatically enhances metal cation affinity over previously reported homo[2]catenane analogues. H NMR cation, anion and ion-pair binding studies reveal significant positive cooperativity between the cation and anion binding events in which cation pre-complexation to the catenane subsequently 'switches-on' anion binding.