Superiority of the Supramolecular Halogen Bond Receptor over Its H-Bond Analogue toward the Efficient Extraction of Perrhenate from Water.

A halogen bond-based water-soluble tetrapodal iodoimidazolium receptor, (L-I)(4Br) , exhibited a high degree of efficiency (∼96%) in extracting ReO 4 - from 100% aqueous medium within a wide range of concentrations and of pH values along with excellent reusability. The solid-state X-ray diffraction study showed the trapping of ReO 4 - by (L-I)(4Br) via the Re-O····I halogen bonding interaction. XPS studies also suggested the interaction between I and ReO 4 - through polarization of the electron density of I atoms by ReO 4 - . (L-I)(4Br) is found to be capable of retaining its high extraction efficiency in the presence of competing anions such as F - , Cl - , I - , SO 4 2- , H 2 PO 4 - , CO 3 2- , NO 3 - , BF 4 - , ClO 4 - , Cr 2 O 7 2- , and a mixture of these anions. Interestingly, (L-I)(4Br) was found to be superior in ReO 4 - extraction as compared to its hydrogen-bond donor analogue, (L-H)(4Br) , as confirmed by a series of control experiments and theoretical calculations. Our synthesized dipodal and tripodal halogen bond donor receptors and their H-analogues validated the superiority of these classes of supramolecular halogen bond donor receptors over their hydrogen-bond analogues. (L-I)(4Br) also showed superior practical applicability in terms of the removal of ReO 4 - at anion concentrations as low as ∼100 ppm, which was a major shortcoming of (L-H)(4Br) .