Cyclobis(paraquat-p-phenylene). A Tetracationic Multipurpose Receptor

The salt 1ṁ4PF6·3CH3CN is a new type of host molecule, which shows similarities to zeolites but is constructed from organic and inorganic ions. The macrocyclic tetracation 1 can be prepared in two steps from bipyridine and 1,4‐bis(bromomethyl)benzene. Calculations and X‐ray crystallography showed the tetracation to have a box‐like structure in which the p‐phenylene and paraquat units are slightly bent. The PF 6⊖‐salt of 1 is soluble in organic solvents, the Cl⊖ salt in water. 1·4PF6 in acetonitrile forms weak inclusion complexes with dimethoxybenzenes, which are stabilized by charge‐transfer interactions. Structural studies of the inclusion complexes show that the electron‐rich guest molecules are located in the cavities (2); because of the stapling of the alternating tetraction and anion/neutral molecule layers these cavities take the form of channels.