First Pseudorotaxane-Like [3]Complexes Based on Cryptands and Paraquat: Self-Assembly and Crystal Structures

A new cryptand, bis(1,3,5-phenylene)tri(1,4,7,10-tetraoxadecyl) (3a), has been synthesized in
good yield from bis(5-hydroxy-1,3-phenylene)-26-crown-8 (2a) and tri(ethylene glycol) ditosylate using
pseudo-high dilution conditions. 3a forms a strong 1:1 complex with paraquat (1) in acetone solution with
a high apparent association constant, 1.4 × 104 M-1. A stoichiometry of 1:1 was also observed by mass
spectrometry in the gaseous state. However, in the solid state, as determined by X-ray crystallography,
the two complexes of 3a and the previously reported homologous cryptand, bis(1,3,5-phenylene)tri(1,4,7,10,13-pentaoxatridecyl) (3b), with paraquat (1) have 2:1 stoichiometry. A unique feature of these
trimolecular pseudorotaxane-like complexes is that the guest occupies parts of the cavities of two cryptand
molecules. For the first time it was found that in cryptand-based complexes, different stoichiometries are
possible for the same host−guest pair.