PhD Studentship: Spin-Crossover Compounds: Switchable Materials From Simple Metal Complexes

Funding

EPSRC Doctoral Training Partnership Studentship offering the award of fees, together with a tax-free maintenance grant of £19,237 per year for 3.5 years. 

Lead Supervisor’s full name & email address

Professor Malcolm Halcrow – m.a.halcrow@leeds.ac.uk

Co-supervisor name(s)

To be confirmed

Project summary 

Spin-crossover is a high-spin-to-low-spin transition at a transition metal centre, in response to a change in temperature or pressure. This is common in some types of transition metal compound, and especially in iron chemistry. While the molecules in a material undergo spin-crossover individually, it leads to large changes in their size and shape which are propagated through the material in the solid state.

As one molecule undergoes the transition and changes its size, it causes a change in pressure in the crystal lattice that in turn promotes the transition in its nearest neighbours. These effects are transmitted through a crystal lattice at differing rates, depending on the strength of the interactions between molecules. Hence, whether a particular material undergoes spin-crossover abruptly or gradually, with temperature or with time, is controlled by its crystal packing. As such, spin-crossover materials are good test-beds for theories about crystal engineering.

Spin-crossover transtions also affect several physical properties of a solid material including its colour, magnetic moment, dielectric constant, hardness and size. These properties have been harnessed in materials applications such as thermochromic inks; stimuli-responsive polymers; switchable microwave absorbers; and solid state refrigeration. Moreover, nanostructures of spin-crossover materials retain their switching properties down to 30 nm length scales, and spin-crossover in single molecules has been detected inside a scanning tunneliing microscope (STM). Spin-crossover nanomaterials science is becoming increasingly sophisticated, and SCO nanoparticle constructs have performed well in prototype binary memory devices.

Some spin-crossover materials also exhibit thermal hysteresis in their transitions; these are most suitable for the applications mentioned above. Whether a compound undergoes spin-crossover gradually or abruptly, with or without hysteresis, is controlled by the crystal packing in the bulk material rather than the molecule itself. We aim to understand the relationship between structure and function, so we can design new spin-crossover materials from scratch. We are also pursuing different ways to incorporate new functionality into spin-crossover materials.

We have projects in various aspects of this chemistry, involving organic and inorganic synthesis; crystallography and powder diffraction; solid and solution-phase magnetic measurements; and other techniques as appropriate. Current goals include understanding the principles for designing spin-crossover crystals with bespoke switching properties; new liquid crystals and other soft materials showing spin-crossover switching properties; and, understanding and developing solid state refrigeration by spin-crossover materials.

You can find a short introduction to spin-crossover and its applications is in Chemical Communications 2013, 49, 10890.

Please state your entry requirements plus any necessary or desired background

First or Upper Second Class UK Bachelor (Honours) or equivalent

Subject Area

Inorganic Chemistry, Materials Chemistry

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