Halocarbon Encapsulation via Halogen···π Interactions in a Bispyrazole-Based Cryptand

A novel bispyrazole-based expanded cryptand was synthesized via Schiff base condensation reaction having an internal cavity of 160 A3 with a hydrophobic nature. The cryptand features electron-rich multiple pyrazole rings for enhanced weak noncovalent interactions with the guest molecules. The host–guest capabilities of the cryptand were investigated for encapsulation of the most inactive halogen bond donor molecules (having small σ-hole size), namely, CH2Cl2, CHCl3, CCl4, C2HCl3, C2H4Cl2, and C2H4Br2. Analysis of crystal structures clearly revealed that halogen bonding (C–Cl/Br···π (pyrazole)) and hydrogen bonding (C–H···π(pyrazole)) interactions played a key role in stabilizing the halogenated guests inside the hydrophobic cavity of cryptand. At the same time, the cage is efficiently able to exclude hydrophilic solvent molecules, like, water and methanol, suggesting the hydrophobic nature of the cavity. Due to the comparably large σ-hole in C2H4Br2, it showed the strongest halogen bonding interaction wit...