Spin crossover (SCO) describes switches in the electronic spin configuration of transition metal ions in molecular and supramolecular coordination compounds. SCO occurs in response to external stimuli, especially temperature, but also pressure or UV/visible light irradiation. The impact of SCO on properties such as colour and magnetism can be dramatic. Fundamental interest in SCO stems from a desire to understand how even very minor changes in intra- and inter-molecular interactions can have such a profound impact on bulk behaviour. Proper understanding of SCO could allow prediction and control of key features of the spin transitions, a realisation that has inspired ideas for novel types of molecular sensors, displays and magnetic memory devices.

Despite the remarkable progress, more work is needed to explain the fundamental relationship between molecular structure and SCO. The most important mechanism for controlling SCO is the immediate chemical environment experienced by the metal ion, i.e., the ligands. Innovative ligand design is critical, and we now propose the first systematic study into how a type of ligand referred to as carbon nanohoops can be used to manipulate and understand SCO. Our preliminary work on SCO nanohoops was recently published in Angew. Chem. Int. Ed. 2021, 60, 3515.

The objectives of the project are to:

1. Develop efficient synthetic routes to a family of bipy-embedded carbon nanohoop ligands of varying sizes, and to use these ligands to synthesis spin crossover complexes containing one, two or three iron(II) centres;

2. Determine the molecular structures of the iron-nanohoops and their magnetic susceptibility properties, leading to a robust structure-property relationship that allows variations in the spin crossover properties to be understood in terms of well-defined intra- and inter-molecular interactions;

3. Use the larger iron-nanohoop SCO complexes as hosts for fullerene guests, and to use the host-guest interactions as a tool for tuning intermolecular cooperativity in the solid-state;

4. Train the PhD student in a variety of synthetic and physical/analytical techniques, complemented by training in transferrable skills, ultimately supporting a talented professional researcher achieve their career goals.

The focus on nanohoop-fullerene chemistry is an opportunity to develop a type of SCO material in which noncovalent host-guest interactions trigger the spin transitions. To help with this, the student will spend a three-month placement at the University of Oregon, USA, working with our collaborator, Prof. Ramesh Jasti, on various aspects of supramolecular chemistry. Success with this aspect will advance the frontiers of spin crossover, nanohoop chemistry, crystal engineering and metallosupramolecular chemistry, emphasizing the multidisciplinary nature of the project.

Shortlisted candidates will be invited to attend an interview in December. The start date of the project will be 20/09/2023.