Halogen bonding-based anion coordination in calixarene/inorganic halide/diiodoperfluorocarbon assemblies

Tuning the aggregation of an amphiphilic anionic calix[5]arene by selective host–guest interactions with bola-type dications

Bola-type dications of different length drive the formation of head-to-tail or capsular supramolecular amphiphiles and, in turn, that of the final aggregates.

Guest-length driven high fidelity self-sorting in supramolecular capsule formation of calix[5]arenes in water

Only homocapsules 1⊃NC8N⊂1 and 2⊃NC10N⊂2 are selectively formed out of ten potentially different products.

Self-sorting assembly of a calixarene/crown ether polypseudorotaxane gated by ion-pairing

A polypseudorotaxane composed of a calix[5]arene-diammonium supramolecular polymer and dibenzo-24-crown-8 wheels self-assembles only in the presence of superweak counterions

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The 1:1 co-crystal of triphen-yl(2,3,5,6-tetra-fluoro-benz-yl)phospho-nium bromide and 1,1,2,2-tetra-fluoro-1,2-di-iodo-ethane

The title compound, C₂₅H₁₈F₄P⁺·Br⁻·C₂F₄I₂, is a 1:1 co-crystal of triphen­yl(2,3,5,6-tetra­fluoro­benz­yl)phospho­nium (TTPB) bromide and 1,1,2,2-tetra­fluoro-1,2-di­iodo­ethane (TFDIE). The crystal structure consists of a framework of TTPB cations held together by C—H⋯Br inter­actions. In this framework, infinite channels along [100] are filled by TFDIE mol­ecules held together in infinite ribbons by short F⋯F [2.863 (2)–2.901 (2)Å] inter­actions. The structure contains halogen bonds (XB) and hydrogen bonds (HB) in the bromide coordination sphere. TFDIE functions as a monodentate XB donor as only one I atom is linked to the Br⁻ anion and forms a short and directional inter­action [I⋯Br⁻ 3.1798 (7) Å and C—I⋯Br⁻ 177.76 (5)°]. The coordination sphere of the bromide anion is completed by two short HBs of about 2.8 Å (for H⋯Br) with the acidic methyl­ene H atoms and two longer HBs of about 3.0 Å with H atoms of the phenyl rings. Surprisingly neither the second iodine atom of TFDIE nor the H atom on the tetra­fluoro­phenyl group make any short contacts.

Structure and energetics of gas phase halogen-bonding in mono-, bi-, and tri-dentate anion receptors as studied by BIRD

Complexes of mono-, bi- (RB), and tridentate (RT) receptors with a range of anions (Cl(-), Br(-), I(-), NO3(-), H2PO4(-), HSO4(-), and tosylate (TsO(-))) have been studied in the gas phase by both experimental and theoretical methods. Temperature dependent blackbody infrared radiative dissociation (BIRD) experiments were performed on complexes of C8F17I with Br(-) and I(-), RB with I(-), NO3(-), HSO4(-), H2PO4(-), and TsO(-), and RT with I(-), HSO4(-) and TsO(-) and the observed Arrhenius parameters are reported here. Master equation modeling of the BIRD kinetics data was carried out to determine threshold dissociation energies. Geometry optimizations and thermochemistry calculations were performed using the B3LYP/6-31+G(d,p) level of theory. Additional single point energies were calculated using MP2/6-311++G(2d,p). Results were examined in terms of the binding order of various anions as well as the added binding strength from additional halogen bonding (XB) interactions. The relative binding energies of ions were generally consistent with the ordering previously reported from solution phase experiments; however, the relatively strong binding of H2PO4(-) to the bidentate receptor contrasted the solution phase observation of oxoanions having weaker interactions when compared to halides. An increase in the energy required to remove the same anion from the tridentate receptor when compared to the bidentate and monodentate receptors is explained as being due to the increase in halogen bonding interactions. The possibility of mixed halogen and hydrogen bonded complexes were considered.