The Structure of the Cyclodextrin Complex. XIII. Crystal Structure of β-Cyclodextrin–1,4-Diazabicyclo[2.2.2]octane Complex Tridecahydrate

Abstract

Abstract The crystal structure of β-cyclodextrin–1,4-diazabicyclo[2.2.2]octane complex tridecahydrate was determined by the X-ray method. The crystal is monoclinic with the space group P21, Z=2, a=15.395(2), b=16.598(1), c=15.441(2) Å, and β=117.35(1)°. The structure was solved by inspection of a Patterson map and a 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 5649 reflections (sinθ⁄λ<0.61). The β-cyclodextrin molecule is in the shape of a distorted and truncated heptagonal pyramid. Two of seven primary hydroxyl groups are in a gauche-trans conformation, the others being in a gauche-gauche conformation. Secondary hydroxyl groups form intramolecular hydrogen bonds between adjacent glucose residues. The guest 1,4-diazabicyclo[2.2.2]octane is almost fully included in the cavity of β-cyclodextrin. Its methylene groups are in van der Waals contact with the methine groups and the glycosidic oxygen atoms at the interior surface of β-cyclodextrin, while two nitrogen atoms form hydrogen bonds with a water molecule and a secondary hydroxyl group of the neighboring β-cyclodextrin. β-Cyclodextrin molecules are arranged nearly parallel to the crystallographic ac plane to form a corrugated sheet of molecular layer. All of the thirteen water molecules fill vacant spaces between the molecular layers, forming a hydrogen-bond network in the crystal.