A new crystal form of beta-cyclodextrin-ethanol inclusion complex: channel-type structure without long guest molecules

摘要

A new crystal form of beta-cyclodextrin (beta-CD)-ethanol-dodecahydrate inclusion complex [(C_6H_10O_5)_7·0.3C_2H_5OH·12H_2O] 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)°. 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-H, O-6-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-W-6) and in the interstics between the beta-CD macrocycles (W-7-W-8). The latter forms a cluster that is hydrogen bonded together and to the neighboring beta-CD O-H groups.