Crown ether alcohols. 1. Crystal and molecular structure of the complex between sym-hydroxydibenzo-14-crown-4 and water molecules ([C₁₈H₂₀O₅]-1.25[H₂O]-0.125[CH₃OH]) including interesting water-methanol channels

The synthesis and crystal structure of the title compound are described. Single-crystal X-ray structure analysis indicates 8 formula units in the unit cell of parameters a = 16.024 (1) Å and c = 13.076 (1) Å. The space group is 14. Direct methods yielded the structure, which was refined by least-squares techniques to a final R factor of 0.038 for 1533 independent observations. A water molecule forms a 1:1 neutral complex with the crown ether alcohol. In this complex, the water molecule is hydrogen bonded to the crown ether hydroxyl group. Four monohydrate complexes are hydrogen bonded to a central water molecule in a perfect tetrahedral geometry and to an apical methanol molecule. Unusual water-methanol channels are found in this structure. The crystal packing of the complex includes hydrophilic water-methanol channels which are surrounded by hydrophobic cylinders consisting mainly of benzo rings and methylene groups. The crystal structure provides a model for the encapsulation of water molecules by hydrophobic regions with potential application for the formation of hydrophilic pores in biological bilayers.