The Structure of the Cyclodextrin Complex. XVIII. Crystal Structure of β-Cyclodextrin–Benzyl Alcohol (1:1) Complex Pentahydrate

Abstract

Abstract The crystal structure of the β-cyclodextrin–benzyl alcohol (1:1) complex pentahydrate was determined by the X-ray diffraction method. The crystal is monoclinic with the space group P21, Z=2, a=15.356(3), b=10.101(2), c=20.869(3)Å, and β=109.90(1)°. The structure was solved by an inspection of a Patterson map and a trial-and-error method combined with a rigid-body least-squares technique. The structure was refined using the block-diagonal least-squares method to an R-value of 0.066 for 5290 reflections (sinθ⁄λ<0.63). The β-cyclodextrin molecule is somewhat elliptically distorted from the regular heptagonal symmetry because of the inclusion of a planar molecule. One primary hydroxyl group shows a gauche-trans conformation, while the others are in a gauche-gauche conformation. The secondary hydroxyl groups form intramolecular O(2)–H···O(3′) or O(3′)–H···O(2) hydrogen bonds, which maintain the round structure of β-cyclodextrin. The guest benzyl alcohol molecule is fully enclosed within the host cavity. Water molecules are distributed in intermolecular spaces between β-cyclodextrin molecules. The phenyl group of the guest is located at the primary hydroxyl side of the cavity. The hydroxyl group occupies a position at the secondary hydroxyl side of the cavity, and forms hydrogen bonds with adjacent β-cyclodextrin molecules. β-Cyclodextrin molecules are stacked along the b axis to form a typical cage-type structure with a herringbone-like packing pattern.