Interaction between beta-cyclodextrin and 1,10-phenanthroline: uncommon 2:3 inclusion complex in the solid state

The crystallographic structure of the complex formed by beta-cyclodextrin with 1,10-phenanthroline has been studied by X-ray diffraction. The result shows that the complex adopts an uncommon 2:3 stoichiometry in solid state, that is, every complex unit contains three 1,10-phenanthroline molecules and two beta-cyclodextrin molecules, where two 1,10-phenanthroline molecules individually occupy two cyclodextrin cavities, and the third guest molecule is located in the interstitial space between two head-to-head cyclodextrin molecules. The intermolecular hydrogen bonds between the adjacent complex units further link these individual monomers to a channel-type assembly. Furthermore, 1H and 2D NMR spectroscopy has been employed to investigate the inclusion behavior between the host beta-cyclodextrin and guest 1,10-phenanthroline in aqueous solution.