Structure and thermodynamic aspects of macrobicyclic polyether-metal ion interactions

The crystals structure of a K⁺-diptychand-15C5-18C6 iodide complex has been determined from X-ray data. The complexed bicyclic molecule crystallizes in the triclinic space group witha = 9.995(4) Å,b = 10.097(4) Å,c = 13.725(6) Å, = 90.12(3)°, = 93.62(4)°, = 97.56(3)°. The structure was solved using heavy atom methods and refined toR = 0.032 for 3262 independent reflections. In the crystal structure, the K⁺ lies between the two crown ether rings, and is coordinated by the nine donor atoms of the ligand molecule. The complexation properties of the ligand with K⁺ and Na⁺ were studied by titration calorimetry in 90% (v/v) MeOH/H₂O solution. The studies indicate the formation of 1 : 1 ligand : metal ion complexes in both solid state and solution.This paper is dedicated to the memory of the late Dr C. J. Pedersen.