X-ray crystallographic studies on the noncovalent syntheses of supermolecules

An approach to the supramolecular syntheses of discrete multicomponent aggr egates of noncovalently bound molecules, i.e., supermolecules, is described . This approach involved the careful analysis of X-ray crystal structures s o as to permit a gradual increase in superstructural complexity Many elabor ate supermolecules were synthesized noncovalently from dialkylammonium-cont aining cations and crown ethers, following the initial observation that the dibenzylammonium ion threads through dibenzo[24]crown-8 to generate a sing ly stranded, singly encircled [2]pseudorotaxane, principally as a result of [N+-H ... O] and [C-H ... O] hydrogen bond formation. The scope of the fun damental recognition motif obtained from this initial observation was then broadened, through the use of thread-like ions with multiple dialkylammoniu m centers and/or larger crown ethers, so that multiply stranded and/or mult iply encircled pseudorotaxanes could be prepared. Cations bearing both dial kylammonium and crown ether recognition sites were also used for the nocova lent synthesis of a discrete daisy chain supermacrocycle and the basic reco gnition motif was combined with other motifs for the production of a wide r ange of novel superarchitectures. As a greater understanding of the noncova lent interactions governing the self-assembly of the complex superarchitect ures was acquired, new protocols for the noncovalent syntheses of doubly do cked pseudorotaxanes and interwoven supramolecular bundles, including a sup ramolecular analogue of the photosynthetic special pair, were developed. Th e discovery that anions can play a prominent role in the solid-state self-a ssembly of some of the supermolecules was a valuable spinoff of the researc h.