The Structure of the Cyclodextrin Complex. XV. Crystal Structure of Hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin–p-Nitrophenol (1 : 1) Complex Monohydrate

Abstract

Abstract The crystal structure of the hexakis(2,3,6-tri-O-methyl)-α-cyclodextrin (abbreviated to methyl-α-CDx) complex with p-nitrophenol, C54H96O30·C6H5NO2·H2O, was investigated by the X-ray method. The crystal is monoclinic, the space group being P21 with Z=2; the cell dimensions are a=11.307(1), b=14.578(1), c=22.118(2) Å, and β=93.62(1)°. The structure was determined by means of the 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 final R-value of 0.048 for 4976 reflections (sinθ⁄λ<0.54). The methyl-α-CDx molecule has the shape of a truncated hexagonal cone, into which the p-nitrophenol molecule is inserted. The phenolic hydroxyl group is located at the center of the methyl-α-CDx cavity, while the nitro group protrudes outside from the base-side of the host cone and is in contact with the adjacent methyl-α-CDx molecule. The water molecule, which is also located within the cavity, links the methyl-α-CDx and p-nitrophenol molecules by hydrogen bonds. Methyl-α-CDx molecules are stacked along the crystallographic a axis in a heat-to-tail mode to form a channel-type structure.