β-Cyclodextrin-potassium hydroxide-water (1/1/8)
Résumé
C42H70O35.K+.OH-.8H20, Mr = 1335.24, monoclinic, P21, a= 15.223 (5), b = 10.578 (3), c = 20.204 (6) Å, β = 108.37 (7)°, V= 3087 Å^3, Z = 2, Dx = 1.436 Mg m^(-3), λ(Mo Ka) = 0.71073 Å, μ = 1.876 mm^(-1), F(000) = 1420, T= 295 K, final R = 0.080 for 4774 observed reflections. The cyclodextrin molecules are stacked, as monomeric entities, inclined at 43.4° along the twofold screw axis, forming a classical herringbone scheme. Three O atoms, attributed to water molecules, are found inside the cyclodextrin cavity, two of them being hydrogen bonded to the two primary hydroxyl groups which are in a gauche-trans conformation. Six others, present as doublets or singlets of water molecules, are located between the cyclodextrin entities and ensure the packing via hydrogen bonding. The potassium ion is incorporated in an interstitial site and coordinated to six non-water O atoms which belong to four different cyclodextrin units, in a distorted trigonal-prism environment. It is suggested that the balancing negative charge is localized inside the cavity, one of the three water molecules being in fact a hydroxyl anion.
