The Structure of the Cyclodextrin Complex. XVII. Crystal Structure of β-Cyclodextrin–Hexamethylenetetramine (1:1) Complex Hexahydrate

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Abstract
The crystal structure of β-cyclodextrin–hexamethylenetetramine (1:1) complex hexahydrate was determined by the X-ray diffraction method. The crystal ismonoclinic with the space group P21, Z=2, a=15.285(3), b=10.345(2), c=20.118(2) Å, and β=102.14(1)°. The structure was solved by inspection of a Patterson map and the trial-and-error method combined with the rigid-body least-squares technique and refined by the block-diagonal least-squares method to the R-value of 0.056 for 4369 reflections (sinθ⁄λ<0.55). The β-cyclodextrin molecule is slightly distorted from the regular heptagonal structure. The orientation of two primary hydroxyl groups is statistically disordered. The secondary hydroxyl groups form intramolecular hydrogen bonds between adjacent glucose residues. The guest hexamethylenetetramine molecule, being located roughly at the center of the β-cyclodextrin ring, is in van der Waals contact with the interior surface of the host molecule. Two out of four nitrogen atoms of hexamethylenetetramine form N···H–O hydrogen bonds with water and adjacent β-cyclodextrin molecules. β-Cyclodextrin molecules are stacked along the crystallographic b axis, with which the plane through seven glycosidic oxygen atoms makes an angle of 46.7°, forming a “cage-type” packing. Water molecules occupy the intermolecular spaces between β-cyclodextrin molecules.