The Structure of the Cyclodextrin Complex. IX. The Crystal Structure of α-Cyclodextrin– m -Nitroaniline (1:1) Hexahydrate Complex

Abstract

The crystal structure of α-cyclodextrin–m-nitroaniline hexahydrate complex was determined by X-ray analysis. The crystal is monoclinic and the space group is P21 with Z=2. The cell dimensions are: a=8.054(1), b=13.508(1), c=25.331(2) Å, and β=103.90(1)°. The structure was solved by an inspection of a Patterson map and by a trialand-error method. The refinement was done by the block-diagonal least-squares method to the final R-value of 0.11 for 2351 reflections (sinθ⁄λ<0.49). α-Cyclodextrin molecules are stacked along the a axis in the head-to-tail fashion to form a channel-type structure. Most of the primary hydroxyl groups of α-cyclodextrin are in a gauche-gauche conformation and linked by hydrogen bonds directly or through water molecules to the secondary hydroxyl groups of the next α-cyclodextrin molecule along the channel. The guest m-nitroaniline molecules are linearly arranged in the channel. The α-cyclodextrin ring includes the nitrophenyl group, while the amino group protrudes outside from the secondary hydroxyl side of α-cyclodextrin and is hydrogen-bonded to a primary hydroxyl group of the next α-cyclodextrin molecule. Along the channel, m-nitroaniline molecules are linked to each other by a weak N–H···O hydrogen bond between the amino group and the nitro group. Columns formed by the stack of α-cyclodextrin are closely packed in the crystal, and intermolecular spaces are filled with water molecules which form many hydrogen bonds with each other and with α-cyclodextrin.