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

A novel supramolecular host {[Fe(CN) 6 ]·(H-bipy) 3 ·8H 2 O} (1) was obtained by the reaction of K 3 [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 H 2 O vapour and completely excludes CO 2 and other organic solvent molecules (CH 3 OH, CH 3 CN and EtOH). © 2010 The Royal Society of Chemistry.