Crystal structure of β-cyclodextrin–dimethylsulfoxide inclusion complex Original Research Article

β-Cyclodextrin (β-CD) crystallizes from 27% DMSO–water as β-CD·0.5DMSO·7.35H2O in the monoclinic space group P21 with unit cell constants: a=15.155(1), b=10.285(1), c=20.906(1) Å, β=109.86(1)°. Anisotropic refinement of 888 atomic parameters against 9,127 X-ray diffraction data converged at an R-factor of 0.055. The β-CD macrocycle adopts a ‘round’ conformation stabilized by intramolecular, interglucose O-3(n)⋯O-2(n+1) hydrogen bonds. In the β-CD cavity, DMSO, water sites W-1, W-3 (occupancies 0.5, 0.25, 0.75) are not located concurrently with the water site W-2 because the interatomic distances to W-2 are too short (1.56–1.75 Å). DMSO is placed in the β-CD cavity such that its S-atom is shifted from the O-4 plane center to the β-CD O-6-side ca. 0.9 Å and the CS bond which is inclined 13.6° to the β-CD molecular axis. It is maintained in position by hydrogen bonding to water site W-3 and the O-31H group. 7.35 water molecules are extensively disordered in 13 positions both inside (W-1W-4) and outside (W-5W-13) the β-CD cavity. They act as hydrogen bonding mediators contributing significantly to the stability of the crystal structure.