FIRST SPHERE COORDINATION OF DIVALENT METAL-CATIONS BY CYCLODEXTRIN -STRUCTURE OF THE BETA-CYCLODEXTRIN-CALCIUM CHLORIDE-WATER (1 2/11.25)COMPOUND/

The structure of the title compound provides the first illustration of direct coordination of a polyvalent cation, as well as an inorganic a nion, by beta-cyclodextrin (beta-CD). Crystal data: P2(1)2(1)2(1), Z = 4, a = 15.875(1), b = 17.583(1), c = 24.270(2)Angstrom, V = 6775(1)An gstrom(3), R = 0.059 for 4744 unique observed reflections with I>3 sig ma(I). There are two CaCl2 per beta-CD, with no direct contacts betwee n the ions. None of the ions are included within the cyclodextrin cavi ty. The cations are in direct interaction simultaneously with two or t hree beta-CD molecules and an eightfold coordination occurs for both. No disorder was found except for the two water molecules situated insi de the cavity. The crystalline form is a novel monomer-type structure. The beta-CD molecules are stacked as monomer entities inclined at sim ilar to 50 degrees along a twofold screw axis, such that they are arra nged in a new herringbone-like scheme. The overall packing is stabiliz ed by intermolecular interactions between cyclodextrin monomers and by direct coordination to the ions. Moreover, the cohesion is reinforced by hydrogen bonds involving water molecules arranged in infinite chai n motifs traversing the whole structure.