Crystal structure determination of the β-cyclodextrin-p-aminobenzoic acid inclusion complex from powder X-ray diffraction data.

The 1:1 inclusion complex of β-cyclodextrin and p-aminobenzoic acid was prepared and characterized by TG-DTA. The crystal structure of the complex was solved directly from powder X-ray diffraction data using the direct space approach and refined using Rietveld refinement techniques. The complex crystallizes in monoclinic P2(1) space group, with unit cell parameters a=20.7890Ǻ, b=10.2084Ǻ, c=15.1091Ǻ, β=110.825°, V=2997Ǻ(3). The amino group is located at the wide side of the β-cyclodextrin cavity, forming hydrogen bonds with β-cyclodextrin, and the carboxyl group is located at the narrow side. The crystallographic data obtained from powder diffraction data were compared with the single crystallographic data, and the result shows that solving crystal structure of cyclodextrins inclusion complexes of such complexity is accessible to powder diffractionists to some extent.