Kevin Liang is the recipient of a prestigious Hertford College Summer Research Studentship and joins the group for a summer project on MOF crystallisation. Welcome Kevin!
News
Most molecular materials don’t conduct electricity well because the electrons in them can’t travel around easily. Materials that do conduct have pathways for their electrons, formed by overlapping atomic orbitals–the space where electrons usually stay–between molecules. In order to increase the conductivity of a molecular crystal, Nickel 5,6-dihydro-1,4-dithiin-2,3-dithiolate, we used high pressure to squeeze the molecules together.
This work was an international collaboration with some really talented scientists in the RIKEN institute, Japan, Kumamoto University, Japan, and Diamond Light Source synchrotron, UK.
Hengbo and Reizo at RIKEN made the molecular crystals and measured their conductivity under high pressure. They did this by attaching tiny wires to the crystal inside a Diamond Anvil Cell (DAC)–a device that generates pressure larger than found at the bottom of the ocean. They found that, whilst normally the crystal didn’t conduct electricity at all, when it was squeezed its conductivity increased dramatically.
In order to understand why, we used X-ray diffraction to work out the crystal structure–where the atoms are and how they are bonded together. Aided by Chloe and Mark, we fired intense X-ray beams produced at Diamond Light Source through our crystal in the DAC and measure how they scattered. From the scattering, we could show for the first time that the molecules got closer and closer together under pressure.
The final piece in the puzzle came from Takao at Kumamoto, who used theoretical calculations based on the X-ray crystal structures to work out the changes in orbital interactions. And the calculations showed that the orbitals between the molecules indeed overlapped more and more with pressure, explaining why the crystals’ conductivity got higher.
A link to the paper can be found here. It’s Open Access, meaning anyone can read it for free!
Thanks and well done to Hengbo, Takao, Chloe, Reizo and Mark!
We’re very pleased to announce our paper on the crystallization of ZIF-8 has just been accepted! It’s been a challenging piece of work, not least because it all began when we made the surprising observation that crystallization got SLOWER when we increased the concentration of our reactants…
There is an increasingly large amount of interest in metal-organic frameworks (MOFs) for a variety of applications, from gas sensing and separations to electronics and catalysis. Their exciting properties arise from their modular architectures, which self-assemble from different combinations of metal-based and organic building units. However, the exact mechanisms by which they crystallize remain poorly understood, thus limiting any realisation of real “structure by design”. We report important new insight into MOF formation, gained using in situ X-ray diffraction, pH and turbidity measurements to uncover for the first time the evolution of metastable intermediate species in the canonical zeolitic imidazolate framework system, ZIF-8. We reveal that the intermediate species exist in a dynamic pre-equilibrium prior to network assembly and, depending on the reactant concentrations and the progress of reaction, the pre-equilibrium can be made to favour under- or over-coordinated species, thus accelerating or inhibiting crystallization, respectively. We thereby find that concentration can be effectively used as a synthetic handle to control particle size, with great implications for industrial scale-up and gas sorption applications. This finding enables us to rationalise the apparent contradictions between previous studies and, importantly, opens up new opportunities for the control of crystallization of network solids more generally, from the design of local structure to assembly of particles with precise dimensions.
The paper is published with Angewandte Chemie, International Edition and can be found here. A previous version can also be downloaded for free on ChemRxiv.
Many thanks to all co-authors, Diamond for beamtime, SCG Innovation for funding and everyone else that helped out along the way!
Functional Flexible Frameworks: Making Materials inspired by Minerals
Anisha Bahl (student) & Dr Hamish Yeung (supervisor)
This PER project took various models and demonstrations to the Museum of Natural History to explain to people of all ages the structures of minerals, how these have inspired the creation of new framework materials studied by the Yeung and Goodwin groups at Oxford Chemistry, and the potential uses of these materials. Two public displays were held in the Museum’s Central Atrium, where anybody could approach the stand and learn about whichever aspects interested them, and one smaller event with a youth group which took the format of a talk and hands-on discussion.
The project focussed on four minerals–zeolite, perovskite, cristobalite, and quartz–and their corresponding materials–zeolitic imidazolate frameworks, hybrid perovskites, zinc dicyanide and zinc dicyanoaurate. Whilst some of the minerals have uses of their own, in our research we are actively studying the materials, whose structures are chemically derived from the minerals, for a range of applications, including gas storage, computing, and sensing. For each mineral/material pair, we built 200,000,000:1 scale models of their crystal structures using parts custom-ordered from Cochranes of Oxford. These were juxtaposed with a beautiful sample of the mineral from the Museum’s collection (in the photo is an example of quartz), together with hands-on props designed to illustrate the connection between crystal structures and the properties of the minerals/materials. We also displayed information about the minerals’ origins and potential applications of the materials on a series of cards.
In addition to the model sets, we constructed a kit containing all the elements required for an interactive (slightly wet and messy!) demonstration of the molecular sieving properties of the zeolite/zeolitic imidazolate framework pair of models. During the public displays, this demonstration was performed every 10-15 minutes to one side of the model display, and served to direct further attention to the exhibit.
Reflections:
The project was hugely successful with the majority of the feedback showing that the participants both enjoyed and learnt from it. The verbal and written feedback both demonstrated that the information was clearly presented and at an accessible level to those viewing it. Whilst initially aimed at secondary school children, primary school children and even younger really enjoyed the display and many showed a clear understanding of some of the concepts (the photo bottom left shows siblings examining the perovskite structure). Conversely there were many adults who also gained a lot from the experience and comments that they “never understood science at school” were quickly replaced by feedback that it was “very easy to understand and interesting.” The museum also commented that they would be interested in using parts or all of the display in future events. Overall the project was considered a success in the sense that it provided a fun and interesting way for a wide range of people to engage with the Department’s scientific research.
Outcomes:
The models and demonstration are now available as an easily portable kit-in-a-box, for taking to other events, such as science fairs, festivals and schools, in the future. Please get in touch to find out more!
Many thanks to Carly Huggins-Smith and OUM, Soozy Smith (photo permission) and Hanna Bostroem, Chloe Coates & Emily Reynolds for demonstrating.
Anisha’s been hard at work over the last six weeks putting together some fantastic models and hands-on activities that demonstrate some of the inspiration behind our research. And after a couple of trial runs, we’re really excited to be exhibiting them at the Museum of Natural History in Oxford today, 2-4pm!
We’ll be right in the middle of the museum, next to the Iguanadon – you can’t miss us!
Thanks to Oxford University Public Engagement with Research Fund, Cochranes of Oxford for the model parts, and Carly at the Museum for all the support!
Yeung Research Group at UoB 