MOLECULAR MECCANO, 37 SELF-ASSEMBLY AND SELF-ORGANIZATION OF SELF-RECOGNIZING CYCLOPHANES

An analysis is presented of the different contributions that give rise to the packing observed in the crystal structures of a wide range of bipyridinium-based molecular assemblies and supramolecular arrays. It is demonstrated how the various interactions - electrostatic, van der Waals, and pi-pi interactions - that contribute to the solid-state arr angement of these molecules and supermolecules can be utilized in orde r to design a series of tetracationic cyclophanes that can potentially self-organize in a highly ordered way in the solid state by virtue of the fact that they contain pi-electron donors as well as pi-electron accepters. The syntheses of these cyclophanes is outlined and the tuna bility of the self-assembly methodology in their construction is demon strated. One of these tetracationic cyclophanes - comprising pi-electr on-rich hydroquinone rings and pi-electron-deficient bipyridinium unit s - has been shown to pack as highly ordered two-dimensional, mosaic-l ike sheets in the solid state. Its dicationic precursor also forms ext ended pi-pi-stacked layers in the solid state. An analogous cyclophane containing two pi-electron-rich resorcinol rings in place of the two hydroquinone rings - forms, in the solid state, one-dimensional arrays wherein the component resorcinol rings interact through their paralle l pi-pi stacking. It has also been established that the first of the a forementioned tetracationic cyclophanes forms a 1:1 adduct with ferroc ene in both the solution and solid states. X-ray crystallography, perf ormed on the 1:1 adduct, reveals that not only is the ferrocene molecu le complexed in a pi-pi stacking sense within the tetracationic cyclop hane, but the 1:1 adduct also packs in a manner that is remarkably sim ilar to the supramolecular organization of the free cyclophane in the crystalline state.