The Structure of the Cyclodextrin Complex. XII. Crystal Structure of α-Cyclodextrin-1-Phenylethanol (1:1) Tetrahydrate

Abstract

The crystal structure of the α-cyclodextrin-1-phenylethanol (1:1) tetrahydrate, C36H60O30·C8H10O·4H2O, was determined by the X-ray method. The crystal is monoclinic, the space group being P21 with Z=2; the cell dimensions are a=8.176(1), b=23.930(2), c=13.853(1) Å, and β=106.69(1)°. The structure was solved by means of the Patterson map and the trial-and-error method combined with the rigid-body least-squares technique. Refinement was carried out by the block-diagonal least-squares method to the final R-value of 0.040 for 3565 reflections. α-Cyclodextrin molecules are stacked along the a axis in the head-to-tail fashion to form a channel-type structure, and are tilted by 17.0° against the channel axis. Owing to the lateral shift of α-cyclodextrin ring parallel to the molecular plane, neighboring α-cyclodextrin molecules along the channel are linked by only one weak hydrogen bond. The 1-phenylethanol molecule is sandwiched between stacked α-cyclodextrin molecules. S-(−) and R-(+) isomers of 1-phenylethanol are each located at the same position with the statistical disorder of the hydroxyl group with the occupancy of 0.5. Columns formed by the stack of α-cyclodextrin are closely packed, being linked with one another by many hydrogen bonds. Water molecules are located in two kinds of intermolecular spaces between α-cyclodextrin columns.