Crystal structure of a complex of alpha-cyclodextrin with 2-fluoro-4-nitrophenol.3H2O.

The crystal structure of a complex of alpha-cyclodextrin (alpha-CD) with 2-fluoro-4-nitrophenol.3H2O has been determined by the X-ray diffraction technique. The complex crystallizes in space group P2(1)2(1)2(1) with cell dimensions: a = 13.431(3), b = 15.299(4), c = 24.780(5) A. The structure was solved by direct methods and refined to R = 6.7% for 4483 reflections. The crystal structure is isomorphous to the alpha-CD-4-nitrophenol.3H2O complex. The phenyl group is inside the cavity, so that the O-4 hexagon of the alpha-CD is distorted in a systematic manner: the longest diagonal [O-4(G2)...O-4(G5)] is in the direction of the benzene ring. The phenolic OH group protrudes from the secondary OH side of the cavity and the NO2 group is situated on the primary OH side. The hydrophobic F atom is statistically disordered over two sites and is located in the hydrophilic space, just beyond the rim of the secondary OH side of the cavity.