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

Hexakis(2,6-di-O-methyl)-α-cyclodextrin (DIMEA) crystallizes from 1:1 water–acetonitrile as DIMEA-acetonitrile-dihydrate in the orthorhombic space group P212121, unit cell dimensions a=14.2775(5), b=15.7312(5), c=31.1494(11) Å. 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 Å and are located in infinite, hydrophobic channels parallel to the a-axis, which are coated with methyl groups of symmetry-related DIMEA.