Host-Guest Binding Hierarchy within Redox- and Luminescence-Responsive Supramolecular Self-Assembly Based on Chalcogenide Clusters and gamma-Cyclodextrin

Water-soluble salts of anionic [Re(6)Q(8)(CN)(6)](4-) (Q=S, Se, Te) chalcogenide octahedral rhenium clusters react with gamma-cyclodextrin (gamma-CD) producing a new type of inclusion compounds. Crystal structures determined through single-crystal X-ray diffraction analysis revealed supramolecular host-guest assemblies resulting from close encapsulations of the octahedral cluster within two gamma-CDs. Interestingly, nature of the inner Q ligands influences strongly the host-guest conformation. The cluster [Re6S8(CN)(6)](4-) interacts preferentially with the primary faces of the gamma-CD while the bulkier clusters [Re6Se8(CN)(6)](4-) and [Re6Te8(CN)(6)](4-) exhibit specific interactions with the secondary faces of the cyclic host. Furthermore, analysis of the crystal packing reveals additional supramolecular interactions that lead to 2D infinite arrangements with [Re6S8(CN)(6)](4-) or to 1D bamboo-like columns with [Re6Se8(CN)(6)](4-) and [Re6Te8(CN)(6)](4-) species. Solution studies, using multinuclear NMR methods, ESI-MS and Isothermal titration calorimetry (ITC) corroborates nicely the solid-state investigations showing that supramolecular pre-organization is retained in aqueous solution even in diluted conditions. Furthermore, ITC analysis showed that host-guest stability increases significantly ongoing from S to Te. At last, we report herein that deep inclusion alters significantly the intrinsic physical-chemical properties of the octahedral clusters, allowing redox tuning and near IR luminescence enhancement.