Molecular Solid Solutions (MoSS): From Concept to Applications

From pharmaceuticals to snowflakes, seashells to chocolate, and batteries to bones, crystalline materials are everywhere. The ability to control crystallisation is therefore hugely important. This project will address this topic and develop a new strategy for controlling the properties of molecular crystals (crystals of organic molecules), where these form the basis of most pharmaceuticals and agrochemicals. The doping of crystals with impurities is well-established as a powerful method for enhancing the properties of inorganic, metallic and semiconductor materials. This is termed the creation of a solid solution. For example, the addition of < 1.5% carbon to iron produces steel, which is harder, more durable and more resistant to corrosion. By comparison, little is known about the doping of crystals of small organic molecules (molecular solid solutions, MoSS). This is due to the challenges associated with studying these materials, where (i) they are inherently disordered, making them challenging to study experimentally and computationally, (ii) there is a vast reaction space comprising different combinations of host and dopant molecules and reaction conditions (eg. solvent and temperature) and (iii) molecular crystals typically exhibit multiple solid forms, with some compounds able to crystallise in over fifty different structures. Existing data on MoSS suggest that this strategy has enormous potential to control the structures and properties of the product crystals. The introduction of dopant molecules can potentially change the structure (polymorph) and stability of the crystals, produce different crystal morphologies and change the rate of formation and growth of crystals. Importantly, it can also change properties such as solubility and resistance to fracture, which are critical in many applications. By understanding the design rules underlying the formation of MoSS and their structure-property relationships we can therefore learn how to use this strategy to tune the structures and properties of molecular crystals in a predictable way. Our vision is to realise the full potential of MoSS and create a framework of tools, data and understanding that translates MoSS from concept to real-world applications. This will be achieved by: Developing screening, characterisation, modelling and crystallisation strategies to explore the synthesis and structure-property relationships of MoSS. Creating an openly accessible MoSS database of structure-property-crystallisation data. Establishing design rules to predict and anticipate which host:dopant systems can form MoSS. Investigating the effect of MoSS formation on crystal polymorph. Collaborating with industry to study real-world systems and translating the developed methods and knowledge to consumer products. Our team is uniquely placed to succeed in this ambitious project. We combine interdisciplinary expertise in MoSS and crystal engineering, high throughput crystallisation, atomic-scale characterisation, modelling of crystal structure and growth, and data handling and AI methods, with the expertise of leading industrial representatives. With our team of experts, state-of-the-art facilities in Durham, Leeds, and Manchester, and the flexibility provided by a Programme Grant, we aim to revolutionise MoSS research and pave the way for real-world applications. Our work has the potential to transform the formulation of drugs, agrochemicals, and other molecular products of the future, and position the UK as a leader in this new field.