A flexible supramolecular host with a crowned chair octameric water cluster and highly selective adsorption properties

Abstract

A novel supramolecular host {[Fe(CN)₆]·(H-bipy)₃·8H₂O} (1) was obtained by the reaction of K₃[Fe(CN)₆] and 4,4′-bipyridyl (bipy) under an acidic medium (pH ≈ 3). The supramolecular structure of 1 is made up of non-covalent forces viz. hydrogen bonding and Π–Π interactions. The host houses a discrete octameric water cluster with the conformation of a 1,4-substituted cyclohexane molecule where six water molecules are positioned on the vertices of the cyclohexane ring and the seventh and eighth occupy the 1,4-equatorial positions of the ring. DFT calculations suggest that this conformation is more stable (−73.08 kcal mol^-1) when compared to the a,a conformation. Upon removal of the water molecules, the host network of 1 undergoes a structural transformation and the dehydrated phase exhibits a stepwise uptake of H₂O vapour and completely excludes CO₂ and other organic solvent molecules (CH₃OH, CH₃CN and EtOH).