Anion-binding properties of π-electron deficient cavities in bis(tetraoxacalix[2]arene[2]triazine): a theoretical study.

The anion recognition by synthetic host molecules is an important theme in supramolecular chemistry. Bis(tetraoxacalix[2]arene[2]triazine) is a conformationally rigid cage molecule with three V-shaped clefts, each constituted by two electron-deficient triazine rings and two aryl C-H moieties. Its halide-binding properties are investigated in this work by quantum chemistry methods. The calculated Gibbs free energies display similar trends as the experimental observations. It has been shown that different types of noncovalent interactions including H-bond, anion-π, and lone-pair-π interactions are concurrent, leading to a cooperative effect. The respective contributions of the interactions to the overall stability are evaluated by using appropriate reference systems, with the anion-π interactions found to be as significant as the hydrogen bond interactions. In addition, in the presence of a water molecule, the stability of the ternary complexes has enhanced greatly in comparison with the binary complexes. Investigations of the solvent effect by the continuum solvent model show that the anion binding energies decrease with increasing solvent polarities. The weak halide binding energies in solution indicate that the reversible binding interactions with bis(tetraoxacalix[2]arene[2]triazine) can offer potential applications for anion transport in the membrane environment.