Crystal structure of hexakis(2,6-di-O-methyl)-α-cyclodextrin–acetonitrile dihydrate: a channel formed by methyl groups harbors a chain of five partially occupied water sites

Abstract Hexakis(2,6-di- O -methyl)-α-cyclodextrin (DIMEA) crystallizes from 1:1 water–acetonitrile as DIMEA-acetonitrile-dihydrate in the orthorhombic space group P 2 1 2 1 2 1 , unit cell dimensions a =14.2775(5), b =15.7312(5), c =31.1494(11) A. Refinement of the structure against 5540 X-ray diffraction data converged at an R factor of 0.083. The macrocycle exhibits a ‘round’ conformation and is stabilized by intramolecular, interglucose O-3–H( n )⋯O-2( n +1) and C-6–H( n )⋯O-5( n +1) hydrogen bonds. Acetonitrile is included in the central cavity of DIMEA and held in position by C-5–H⋯N interactions. The two water molecules in the asymmetric units are distributed over six sites. One is fully occupied due to hydrogen bonding to O-3 groups of two symmetry-related DIMEA molecules, whereas the five remaining sites show occupancies between 0.15 and 0.25. These sites are in hydrogen bonding contact with O⋯O distances between 2.59 and 3.50 A and are located in infinite, hydrophobic channels parallel to the a -axis, which are coated with methyl groups of symmetry-related DIMEA.