title: A new crystal form of beta-cyclodextrin-ethanol inclusion complex: channel-type structure without long guest molecules.
abstract: A new crystal form of beta-cyclodextrin (beta-CD)[bond]ethanol[bond]dodecahydrate inclusion complex [(C(6)H(10)O(5))(7).0.3C(2)H(5)OH.12H(2)O] belongs to monoclinic space group C2 (form II) with unit cell constants a=19.292(1), b=24.691(1), c=15.884(1) A, beta=109.35(1) degrees. The beta-CD macrocycle is more circular than that of the complex in space group P2(1) [form I: J. Am. Chem. Soc. 113 (1991) 5676]. In form II, a disordered ethanol molecule (occupancy 0.3) is placed in the upper part of beta-CD cavity (above the O-4 plane) and is sustained by hydrogen bonding to water site W-2. In form I, an ethanol molecule located below the O-4-plane is well ordered because it hydrogen bonds to surrounding O-3[bond]H, O-6[bond]H groups of the symmetry-related beta-CD molecules. In the crystal lattice of form I, beta-CD macrocycles are stacked in a typical herringbone cage structure. By contrast, the packing structure of form II is a head-to-head channel that is stabilized at both O-2/O-3 and O-6 sides of each beta-CD by direct O(CD)...O(CD) and indirect O(CD)...O(W)...(O(W))...O(CD) hydrogen bonds. The 12 water molecules are disordered in 18 positions both inside the channel-like cavity of beta-CD dimer (W-1[bond]W-6) and in the interstices between the beta-CD macrocycles (W-7[bond]W-18). The latter forms a cluster that is hydrogen bonded together and to the neighboring beta-CD O[bond]H groups.
authors.affiliation: Department of Chemistry, Faculty of Science, Chulalongkorn University, Phyathai Rd., Pathumwan, Bangkok 10330, Thailand. mam@atc.atccu.chula.ac.th
authors.forename: Thammarat
authors.initials: T
authors.lastname: Aree
authors.forename: Narongsak
authors.initials: N
authors.lastname: Chaichit
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D003505:Cyclodextrins / Q000737:chemistry*; D000431:Ethanol / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D014867:Water / Q000737:chemistry; D047392:beta-Cyclodextrins
chemical_list: D003505:Cyclodextrins; D047392:beta-Cyclodextrins; D014867:Water; D000431:Ethanol; C031215:betadex