P. Charpin

First sphere coordination of divalent metal cations by cyclodextrin: structure of the β‐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 anion, by β-cyclodextrin (β-CD). Crystal data: P212121, Z = 4, a = 15.875 (1), b = 17.583 (1), c = 24.270 (2) A, V = 6775 (1) A3, R = 0.059 for 4744 unique observed reflections with I > 3σ(I). There are two CaCl2 per β-CD, with no direct contacts between the ions. None of the ions are included within the cyclodextrin cavity. The cations are in direct interaction simultaneously with two or three β-CD molecules and an eightfold coordination occurs for both. No disorder was found except for the two water molecules situated inside the cavity. The crystalline form is a novel monomer-type structure. The β-CD molecules are stacked as monomer entities inclined at ~50° along a twofold screw axis, such that they are arranged in a new herringbone-like scheme. The overall packing is stabilized 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 chain motifs traversing the whole structure.

Anhydrous uranyl crown-ether complexes. 1H nuclear magnetic resonance and x-ray study

Abstract The preparation of anhydrous uranyl perchlorate complexes with 18-crown-s (I) and with dicyclo- hexyl-18-crown-6 (II) is described. Single crystals have been obtained and X-ray crystallographic data are discussed. Significant induced shift are observed in the 1H nmr spectra of the complexes in acetonitrile solution. These arise from short interatomic distances between the crown-ether protons and the paramagnetic UO2+2 cation as would be expected in insertion complexes. A visible spectroscopy study of the decomplexation of these compounds by DMSO or water is also presented.

The Heptakis-(2,6-di-O-methyl)-β-cyclodextrin Inclusion Complex with Acetic Acid

A novel monomer-type structure of heptakis-(2,6-di-O-methyl)-β-cyclodextrin in a typical monoclinic herringbone scheme has been determined by single crystal X-ray diffraction. Crystal data: space group P21, Z = 2, a = 15.165(6), b = 10.613(3), c = 23.188(8) Å, β = 102.02(4)°, V = 3650(3) Å3 and R = 0.094 for 2933 observed MoKα reflections with I > 3σ(I). A unique water molecule located in the intermolecular spaces, reinforces the cohesion between the herringbone chains. The analysis of the electron density distribution suggests that an acetic acid molecule is trapped within the macrocycle cavity, alternately with a water molecule.

Uranium(IV)-crown-ether complexes and cryptates. 1H Nuclear magnetic resonance study, and X-ray crystal and molecular structure of tetrachloro-(2,5,8,15,18,21-hexaoxatricyclo[20.4.0.09,14]hexacosane)uranium(IV)

1 H N.m.r. evidence for direct co-ordination of uranium to the oxygen atoms in a new UCl4-dicyclohexyl-18-crown-6 complex is confirmed by an X-ray structural determination; several uranium(IV) salt–crown-ether complexes and cryptates also exhibiting very large n.m.r. shifts are reported.

X-Ray and Atomic Force Microscopy Structures of Short Chain Amphiphilic Cyclodextrins

Cyclodextrins rendered amphiphilic by remarkably short substituents chains have been shown to form stable molecular layers1,2. The results deduced from compression isotherms of Langmuir films at the air-water interface led us to propose the formation of amphiphilic cyclodextrin multilayers and the existence of a highly rigid (solid) system. As the physical characteristics of the Langmuir films might be correlated with bulk solid-state structures, comparative crystallographic studies have been undertaken for α-, β- and γ-cyclodextrins selectively persubstituted at the primary face with very short hydrophobic groups.