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Building Precise Molecular Architectures to Unlock Remarkable f-Element Properties

Periodic Reporting for period 2 - F-ELEMENT_ARCHITECT (Building Precise Molecular Architectures to Unlock Remarkable f-Element Properties)

Reporting period: 2021-03-01 to 2022-08-31

The f-elements, the lanthanides and actinides, are of huge technological importance. Societal benefits of the f-elements include optical and magnetic devices, batteries and civil nuclear power. However, f-element chemistry is underdeveloped compared to the s-, p- and d-blocks of the periodic table, and we now need to build a bigger knowledge platform to underpin current and future f-block applications. In this project, we target the synthesis of f-element complexes with precise linear or trigonal geometries. Such architectures are often difficult to achieve as f-element chemical bonding regimes are predominantly ionic, and this tends to favour the formation of different shapes.

Linear and trigonal f-element molecules have been shown to exhibit maximised magnetic and optical properties; for example axial dysprosium single-molecule magnets have shown magnetic memory effects at the highest temperatures to date, which could lead to high-density data storage applications. Linear and trigonal f-element compounds are also highly effective in stabilising unusual phenomena, such as low oxidation state compounds, which are of fundamental importance but have previously shown applications in organic synthesis. The relatively simple shapes of linear and trigonal molecules provides additional advantages in that their physical characterisation can be easier to interpret in high symmetry, and calculations to benchmark these results can be cheaper.

By using a combination of synthesis, characterisation and computational methods we target high-performing single molecule magnets, unusual low oxidation state compounds, and challenging measurements of small amounts of covalency in f-element chemical bonding. Together, these studies will push forward the research agenda in their respective disciplines, and will provide a combination of data that can be applied in future to real-world f-element technologies, such as improving recycling and separations platforms in nuclear fuel processes to increase efficiency and produce less waste.
In the first 18 months of the project the team have performed a combination of synthesis, measurements and calculations to provide a large number of results. Our primary mechanism for dissemination of these results is in peer-reviewed journal articles, and as many of these projects are at an early stage they are not yet ready for publication; to prevent breaking embargos and export controls regulations, unpublished results will not be disclosed here. The results are also at too early a stage for consideration of commercial exploitation, thus we focus on dissemination activities here.

So far the team have worked with collaborators to publish primary research on: (i) rare examples of lanthanide phospholyl compounds (Dalton Trans., 2020, 49, 6504, DOI:10.1039/D0DT01241F); (ii) samarium chalcogenide compounds as models for gadolinium radicals with giant spin-coupling (Inorg. Chem., 2020, 59, 7571, DOI:10.1021/acs.inorgchem.0c00470); (iii) the first structurally authenticated thorium-silicon bond to facilitate a comparison of covalency with an analogous compound containing a uranium-silicon bond (Chem. Commun., 2020, 56, 12620, DOI:10.1039/D0CC06044E); and (iv) complementary studies in d-block chemistry where we reported the first example of a structurally characterised derivatised ferrocene anion, providing new insights into electronic structures of the classical metallocene family (Nature Chemistry, 2021, 13, 243, DOI:10.1038/s41557-020-00595-w). The team have also contributed to three literature reviews in this area of relevance to the core aims of the grant to use time spent in pandemic shutdowns to good effect: (i) a review of f-element heavy group 14 solution chemistry (Chem. Sci., 2020, 11, 10871, DOI: 10.1039/D0SC04655H); (ii) a review of f-element phospholyl chemistry (Chem. Eur. J. 2021, DOI:10.1002/chem.202005231); and, (iii) a review of dysprosium alkoxide and aryloxide single-molecule magnets (Chem. Eur. J. 2021, DOI:10.1002/chem.202100085).

Dissemination activities over the last 18 months at conferences have been hugely impacted by the pandemic, with many conferences delayed or cancelled. There have therefore been few opportunities for the group to give oral and poster contributions about this work. However, the group has still presented work from this project at: (i) Invited seminars at Imperial College London and Newcastle University; (ii) numerous talks at the University of Manchester to current staff and students; (iii) Online conferences, including the 54th Annual International Meeting of the RSC ESR Spectroscopy Group.

Outreach opportunities have also been greatly limited by the pandemic. However, the group have managed to present the research activities of this project to schoolchildren and the general public by: (i) An online seminar on single-molecule magnets for the University of Manchester ChemSoc and PASS-organised Meet the Academics Event; (ii) A blog on metallocene anions for the Nature Chemistry Community website; and, (iii) A radio interview on on single-molecule magnets for the Einstein A Go-Go show on 3RRRFM in Melbourne, Australia.
We have shown over the last 18 months that despite the impact of the pandemic and the challenges associated with reduced/restricted lab time and remote working that we are able to continue progress towards the project aims. We have published advances in f-element synthesis, measurement and calculations, and we are now drafting manuscripts with advances that go beyond the state-of-the-art in f-element chemistry. We have continued to grow our activities with established collaborators, and instigated new collaborations, to target major advances in a wide range of technical areas and research fields. The results that will be obtained by the end of the project include the synthesis and study of f-element compounds with unusual geometries and oxidation states by innovative methods, leading to new insights into relaxation mechanisms of gold standard single-molecule magnets and unique approaches to measurements of f-element covalency. Taken together these studies will provide new insights into f-element electronic structures, for future exploitation in applied fields.