Mapping out crystallization

I have a newfound respect for cartographers. They map out landscapes with an amazing eye for detail and clarity, picking out the essential roads, hills and valleys with ease. In my latest paper, I’ve been trying to do the same for chemical reactions…

MOF crystallisation landscape

The “landscapes” of chemical reactions are the hills and valleys of potential energy, and the pathways molecules take to pass between them as they transform. To map out reactions, we can’t just measure them up like towns and cities (molecules are so tiny!), so instead we have to use other methods like spectroscopy to gauge how the molecules involved transform over time, and use that information in clever ways to deduce how much energy the transformations take. This has been done for decades for gases and molecules in solution – it’s the area of Physical Chemistry – but it’s not been done much for reactions that transform molecules in solution to solid materials.

The crystallisation of coordination polymers is one such reaction: one that I’ve been interested in ever since I started doing research trying to design them. But for any kind of predictability – to guide our choice of temperature, time, solvents etc. – we need to know something about their energy landscapes. So some of my collaborators and I went to Diamond synchrotron (more about that trip here) to try to do just that. And, by measuring the rates of formation and dissolution of three related materials, we have been able to work out the activation energies – the heights of the hills that the reaction system has to cross – to make each one.

To the best of our knowledge, this is the first time anyone’s done this for more than one material forming from the same reaction. We now have the information to choose the reaction conditions best for selectively making any one of those materials. What’s more, the methods we used – in-situ X-ray diffraction and some simple kinetics modelling – could potentially be applied to formation reactions of lots of other materials, like MOFs and zeolites. The paper in Angewandte Chemie is here, or in my publication list here.

Thanks Yue, Sebastian, Tony, Dermot and Richard for being such great co-authors!

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