Disorder in Cyclodextrin Clathrates: X-ray Diffuse Scattering Analysis of α-Cyclodextrin Cyclopentanone Hydrate

Abstract

Most of the cyclodextrin clathrates display disorder, consequently the structure determination is often difficult to carry out. Previous studies by X-ray and neutron diffraction have shown that the \alpha-cyclodextrin cyclopentanone hydrate crystallizes in a channel-like structure with hexagonal P6 symmetry. Two inclusion complexes were found in the asymmetric unit; there is an orientational disorder of the guest with six positions found in one host cavity, three in the other. In addition, certain host hydroxyl groups and water molecules were found to be disordered and their disorder was correlated with the guest disorder. In this paper we investigate X-ray diffuse scattering phenomena in order to go further in the interpretation of disorder. Complicated diffuse scattering patterns revealed a variety of disorder phenomena. Some were not shown by the average structure determination. The interpretation of the results (structure in domains, supercell and vacancies) helps to explain the rotational disorder of the guest and some observed strains of the averaged structure. The description of different microstructures may be of interest for crystal growth and inclusion chemistry.