Solid-state NMR and wide-angle X-ray diffraction study of hydrofluoroether/β-cyclodextrin inclusion complex

An inclusion complex (IC) composed of a hydrofluoroether (HFE) guest and a beta-cyclodextrin (beta-CD) host was newly prepared, and the crystalline structure and the thermal stability of the IC were examined using several analytical methods, including wide-angle X-ray diffraction (WAXD), solid-state NMR, thermogravimetric analysis (TGA), TG-mass spectrometry (TG-MS), and quantum chemical calculation. The WAXD patterns and elemental analysis identified that the IC of an HFE/beta-CD form of a channel-type structure, in which one HFE molecule is included in a common cavity of two beta-CD molecules. TGA and TG-MS analysis indicated that the HFE molecules included in beta-CD are hardly evaporated or degraded up to the decomposition temperature of the beta-CD host. Solid-state C-13 NMR indicated that the beta-CD ring structure was deformed by including an HFE molecule in it, and that the F-19 NMR signals of the HFE guest were significantly shifted to higher frequencies by the inclusion due to the dielectric media effect in the cavity of beta-CD. Moreover, the F-19 NMR signals of HFE included in IC were further shifted after annealing at 150 A degrees C, which reflected structural changes in HFE/beta-CD IC caused at elevated temperatures. The WAXD patterns also confirmed that the packing structure along the crystalline b-direction of HFE/beta-CDs, which penetrates the cavities of beta-CDs, was compressed by annealing and transformed to a more stable structure.