Lanthanides and Actinides in the +1 Oxidation State

The lanthanides and actinides, known collectively as the f-block elements, constitute approximately a quarter of the periodic table. The chemical and physical properties of these elements are indispensable to modern society. Lanthanides are at the heart of a huge variety of technological applications, ranging from medical imaging, computer HDDs and bulk magnets, to defence technology and optical materials. The actinides thorium, uranium and plutonium are used in nuclear fission reactors, a technology earmarked for growth as part of the UK's net-zero strategy.

The chemistry and physics of lanthanide and actinide compounds depends strongly on the oxidation state of the metal. For the lanthanides, oxidation state +3 is ubiquitous whereas compounds containing these elements in oxidation states +2 and +4 are known in a limited number of cases. For the early actinides, oxidation states range from +3 up to +6 or +7, and the highly reactive oxidation state +2 has recently been observed. This project will focus on the synthesis and characterization of the first compounds containing the lanthanides and the early actinides (thorium-plutonium) in the elusive +1 or monovalent oxidation state.

The PI's recent report of the first uranium(I) compound signposts a route to a family of monovalent lanthanide and actinide compounds. At the outset, we focus on monovalent lanthanides, aiming to synthesize a series of metallocene-like sandwich compounds and to determine the factors upon which the properties of these unusual compounds depends. In parallel, we will synthesize monovalent metallocenes of the early actinides thorium, uranium, neptunium and plutonium.

A core goal of the project is to combine observations from synthetic and structural chemistry with detailed physical characterization and theoretical studies. This approach will provide quantitative insight into the electronic structure and chemical bonding of monovalent f-elements, including descriptions of the ionic and covalent contributions. The structure-property relationship will be used to design reactivity studies, with an emphasis on small-molecule activation using highly reducing monovalent f-elements. The electronic structure of monovalent lanthanides should be more diverse than for these elements in conventional oxidation states. As a result, contrasting reactivity for neighbouring lanthanides could occur, potentially requiring standard descriptions of f-element chemistry in terms of the lanthanide and actinide contractions to be revised.

In addition, we will embed impact into the project through a new international collaboration with colleagues in Germany, through a programme of engagement activities aimed at inspiring the public with our science, and through the career development of the Sussex team members via participation in various training programmes relevant to the scientific objectives.