International Collaboration in Chemistry: Structural Mechanostereochemistry of Mechanically Interlocked Polymers and Networks

Lead Research Organisation: University of St Andrews
Department Name: Chemistry

Abstract

This project involves a collaboration between Prof J F Stoddart and A M Z Slawin.As we transition now from the world of small mechanically interlocked molecules (MIMs) to higher ordered MIMs and networked structures, we propose to follow our previously successful approach. This approach requires crystallography to play a critical - rather than a supportive - role in the iterative feedback loop in moving systematically from the known to the unknown. The countless relatively simple structures designed, synthesized, and characterized over the years of this collaboration serve as fertile ground for the vision of higher-ordered structures containing multiple mechanically interlocked components arranged in the highly regular architectures of (1) foldamers and (2) metal-organic frameworks that incorporate MIMs. The former - based on pi-electron donor/acceptor interactions - are expected to have unique compression/extension properties by virtue of these intramolecular non-covalent forces - in some ways similar to biomacromolecules - and could be regarded as wholly synthetic models of their naturally occurring counterparts. Furthermore, the potential for highly regular structures, in which alternating electron-rich and electron-poor systems are nearly perfectly aligned, suggest these types of molecules would also exhibit unique electronic properties as well. These types of structures would combine the synthetic precision of organic chemistry with the robustness of crystalline materials, affording a stable platform for a new generation of functional mechanically-interlocked structures, including those that can change their optical properties under mildly oxidative/reductive conditions. Furthermore, metal-organic frameworks (MOFs) that incorporate molecular Borromean Rings - with their potential for octahedral functionalization - as secondary binding units would comprise a unique crystalline material with two distinctly different types of cavities. Each of these compounds poses significant challenges, not only in their preparation which will be carried out by the JFS group, but perhaps more so in their characterization. At the outset, it is essential to understand more fully how such higher-ordered mechanically interlocked structures arrange themselves - both in solution and in the solid state - before attempting more speculative projects. We endeavor then to lay the groundwork for future projects by focusing our efforts on two classes of progressively more complex, but discrete, [n]rotaxanes: (1) those based on electron-donor threads and electron-acceptor rings, and (2) the complementary series comprised of acceptor threads and donor rings, with a heavy emphasis on the preparation of single crystals. Single crystals of these discrete oligorotaxanes will be analyzed by the AMZS group in their world-class crystallography facility at St Andrews. We will use the results of structural investigations to refine theoretical molecular models by providing detailed information about interactions driving crystal formation.

Publications

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Barnes JC (2013) A radically configurable six-state compound. in Science (New York, N.Y.)

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Coskun A (2012) Metal-organic frameworks incorporating copper-complexed rotaxanes. in Angewandte Chemie (International ed. in English)

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Forgan RS (2012) Self-assembly of a [2]pseudorota[3]catenane in water. in Journal of the American Chemical Society

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Forgan RS (2012) Nanoporous carbohydrate metal-organic frameworks. in Journal of the American Chemical Society

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Gassensmith JJ (2012) Polyporous metal-coordination frameworks. in Organic letters

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Gassensmith JJ (2011) Strong and reversible binding of carbon dioxide in a green metal-organic framework. in Journal of the American Chemical Society

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Ke C (2012) Quantitative Emergence of Hetero[4]rotaxanes by Template-Directed Click Chemistry in Angewandte Chemie International Edition

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Smaldone RA (2010) Metal-organic frameworks from edible natural products. in Angewandte Chemie (International ed. in English)