Three Chemical Tales of Serendipity at Work in the Nano Foundry

Date & time

4–5pm 15 October 2013

Location

Law Theatre

Speakers

Sir Professor Fraser Stoddart

Contacts

 Gavin Perri
 61252391

The time has come for us to embrace complexity—despite the fact that everyone has their own definition of it—and put much more emphasis into studying mixtures of interacting molecules. An excellent reason for responding positively to the intellectual challenge posed by systems chemistry is that complexity very often gives rise to emergent properties that are not present in the components of a complex mixture but come to light only as a result of interactions between molecules. The first example of emergent behavior, which I will highlight, is provided by a new class of wholly organic materials based on a 1:1 mixture of neutral aromatic compounds—where donors and acceptors, which also encompass stabilizing hydrogen bonding interactions—form mixed stacks that boast the welcome but elusive property of room temperature ferroelectricity. While the materials’ behavior was unexpected, the molecular basis for it is extremely simple and the superstructure leads directly to the complexity that emerges once the act of crystallization is complete. The result is a material with properties not shared by its components. A second example is provided by the self-assembly, in aqueous alcohol, of infinite networks of extended structures, which we call CD-MOFs, wherein γ-cyclodextrin (γ-CD) is linked by coordination to Group IA metal cations to form metal-organic frameworks (MOFs). CD-MOF-1 and CD-MOF-2, which can be prepared on the gram scale from KOH and RbOH, respectively, form body-centered arrangements of (γ-CD)6 cubes linked by eight-coordinate alkali metal cations. These CD-MOFs exhibit very different properties than γ-CD itself. For a couple of years, I was of the opinion that the nature of the anion accompanying the K+ or Rb+ cation was unimportant. Not so, because if it is AuBr4 –, the situation changes quite dramatically. This third example of emergent behavior constitutes the final act in my three chemical tales of serendipity. We need to come to terms with complex networks that can be periodic, aperiodic or completely random. Complex networks are everywhere to be found: they are all around us. Consider the world-wide web or global stock markets. Reflect on the way birds adopt formations in the sky during migrations or the response of different ecosystems to climate change. In the superorganism formed by certain ant colonies, the ants operate as a unified entity, working together collectively to support the colony. Prediction in the case of complex networks is night impossible. Uncertainty rules the roost—and the unexpected is always just lurking round the corner. While research into complex networks is commonplace in mathematics, physics and biology, as well as in computer science, economics and the engineering disciplines, when it comes to creating and understanding complex networks, chemists have been conditioned by their education and training to avoid them. We have an aversion to mixtures of molecules, yet complex mixtures no longer constitute an intractable problem with rapidly growing access to modern analytical tools, increasingly enlightened approaches to chemical synthesis—often involving one-step procedures starting from inexpensive and readily available starting materials—and the ability to carry out computations on integrated systems over multiple length scales in time and space.
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• Selective Isolation of Gold Facilitated by Second-Sphere Coordination by α-Cyclodextrin, Nature Commun. 2013, 4, Article 1855.
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