We study the formation, organisation and response of functional materials, including metal–organic frameworks, hybrid perovskites and molecular crystals. We use a multi-disciplinary approach to gain new insights into the structure of matter and its behaviour in the crystalline state. We have a particular focus on using in situ techniques to investigate the interesting physics and chemistry that occurs under operating conditions, such as during synthesis, or under high pressure or electric fields. The understanding we develop ultimately leads to better design of new materials, which has impact on fundamental science and new technology.
Formation
Although it is now possible to predict the structure of new functional materials accurately, in order to make them a reality – efficiently, sustainably and economically – we need to know the best conditions under which to make them. Using powerful in situ techniques, including synchrotron X-ray diffraction, we are investigating the driving forces and mechanisms of crystallisation at the molecular level, which leads to greener synthesis and the capability to create novel materials.
In-situ monitoring: “In Situ Observation of Successive Crystallizations and Metastable Intermediates in the Formation of Metal–Organic Frameworks”
Mechanisms of formation: “Control of Metal–Organic Framework Crystallization by Metastable Intermediate Pre‐equilibrium Species”
Driving forces: “Phase Selection during the Crystallization of Metal-Organic Frameworks; Thermodynamic and Kinetic Factors in the Lithium Tartrate System”
Organisation
Materials’ properties are fundamentally governed by their structure – how the components that make them up are arranged in space – and so the ability to control structure is critical. We use crystallographic techniques to examine their structures in great detail at the molecular level, and develop ways to tune structure on multiple length scales using mixtures of different building blocks and new synthesis methods.
Crystallography of chiral MOFs: “Chiral, Racemic and Meso- Lithium Tartrate Framework Polymorphs: A Detailed Structural Analysis”
Mixed-linker frameworks via mechanochemistry: “Ligand-Directed Control over Crystal Structure and Solid Solution Formation in Inorganic-Organic Frameworks”
Nanoscale MOF domains: “Compositional Inhomogeneity and Tuneable Thermal Expansion in Mixed-Metal ZIF-8 Analogues”
Response
Materials do amazing things when subjected to external forces. They can change colour, generate electricity or even expand when they ought to contract. We seek to understand and exploit materials’ structural responses to heat, pressure, chemicals and electric fields, which are important for applications such as batteries, computing and sensing.
Conductivity under pressure: “High Pressure Crystal Structure and Electrical Properties of a Single Component Molecular Crystal [Ni(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate)”
Extreme flexibility: “Hidden negative linear compressibility in lithium L-tartrate”
Chemical sensing: “Strain-based chemical sensing using metal–organic framework nanoparticles”
Metal–organic frameworks and beyond
Our interests lie in understanding a broad range of materials, including coordination polymers, molecular electronic crystals, hybrid perovskites and metal–organic frameworks (MOFs).
MOFs are Chemistry’s equivalent of Tinker Toy®, in which assembly of molecular building blocks into robust, atomically-precise materials leads to structures boasting exceptional properties, including selective gas adsorption, chirality, tuneable mechanics, exotic magnetism, switchable luminescence and ionic conductivity. We look to exploit the synergy between the “metal” and “organic” components to generate new structures for next-generation technologies, and develop advanced approaches to understand their structures and properties.
Tunable mechanics: “Mechanical Tunability via Hydrogen Bonding in Metal-Organic Frameworks with the Perovskite Architecture”
Unusual reactivity: “Topotactic Elimination of Water across a C–C Ligand Bond in a Dense 3-D Metal–Organic Framework”
Techniques
Synthesis of our materials relies on the careful combination of two or more chemical reagents – e.g., the solutions of the metal and organic linker in MOFs – under highly controlled conditions. Temperature, solvent, pH and mixing are crucial to control the chemical reactions that underpin self-assembly and crystallisation in order to generate pure materials for further study.
Characterisation of as-synthesised materials is performed using standard analytical techniques of chemistry and materials science, which probe different aspects of their structure, such as crystallinity (powder X-ray diffraction), chemical functionality (infrared spectroscopy), particle morphology (electron microscopy), thermal stability (thermogravimetry), conductivity (impedance spectroscopy).
Detailed structural analysis is performed to understand our materials better, and the techniques we use depend on what’s of most interest. Single crystal X-ray diffraction can determine exactly where the atoms lie in a material that give rise to its properties; we use in-house diffractometers for routine work and synchrotron X-rays for more complex studies, including high pressure behaviour or challenging materials.
In situ techniques are really useful to study how materials form or behave under a variety of conditions, such as during synthesis or under high temperature, pressure or electric fields. We use them to give unparalleled insight into the fundamental structure-property relationships that govern the behaviour of functional materials.
Computational methods are increasingly being used to improve analysis of our experimental data. For example, sequential Rietveld refinement to powder diffraction data can determine how structures change as a function of time, composition or temperature. We collaborate with experts in computational chemistry, who simulate how atoms interact in our materials, helping to verify and understand our experimental observations.
Central facilities are used to obtain high-resolution experimental data that give cutting-edge insight into the structures of our materials. We also exploit the high flux and tuneable energies of synchrotron X-ray sources, such as Diamond, to perform in-situ experiments.
Yeung Research Group at UoB 