The Structure of the Cyclodextrin Complex. XVI. Crystal Structure of Heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin-p-Iodophenol (1 : 1) Complex Tetrahydrate

The crystal structure of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin–p-iodophenol (1 : 1) tetrahydrate, C63H112O35·C6H5OI·4H2O, was determined by the X-ray method. The crystal is orthorhombic with the space group P212121, Z=4, a=14.997(2), b=21.368(2), and c=28.205(3) Å. The structure was solved by the heavy atom method combined with the rigid-body least-squares technique and refined by the block-diagonal least-squares method to the final R-value of 0.094 for 3268 reflections (sinθ⁄λ<0.49). Heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin is in the shape of a truncated elliptical cone. The macrocyclic ring is remarkably distorted from a regular heptagonal structure. The iodophenyl group of the guest is inserted into the host cavity. The phenolic hydroxyl group protrudes from the cavity, forming hydrogen bonds with two water molecules. The iodine atom is located at the center of the macrocyclic ring, while the benzene ring occupies its position at the base side of the cone. The crystal is built up of columns which are formed by the stack of host molecules in a head-to-tail mode along the two-fold screw axis which is parallel to the crystallographic b axis. Four water molecules fill intermolecular spaces in the crystal.