New year, new arrivals

This month we are joined by Harry Lloyd and Aaron Chambers, who will be starting two exciting, collaborative PhD projects in the group!

Harry is studying time-resolved dynamics of framework materials under electric fields on a joint Diamond Light Source PhD studentship. He’ll be co-supervised by Dr Lucy Saunders and Dr Mark Warren from Diamond, where he’ll spend two years getting hands-on at Beamline I19-1!

Aaron is studying the formation and processing of MOF nanoparticle composites as part of a collaboration initiative between the University of Birmingham and BAM, the Federal Institute for Materials Research and Testing, Berlin. He’ll be co-supervised by Dr Brian Pauw from BAM, where he’ll visit to perform 3-D printing and in-depth structural characterisation.

Diamond PhD studentship

We’re really excited to offer a PhD studentship for 2020 joint with Diamond Light Source, the UK’s national synchrotron facility!

The project is funded for 4 years and the student will spend 2 years at Birmingham, 2 years at Diamond, where they will investigate how the structures of functional materials – including metal–organic frameworks and molecular ferroelectrics – change with applied electric fields.

The student will gain cutting-edge skills in materials synthesis, time-resolved single crystal X-ray diffraction and physical property measurement.

Please see the link above for more information and to register interest. Contact Hamish for any other enquiries.

Squeezing conductivity from a molecular crystal

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!

Pre-equilibrium species in MOF crystallization

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!