Pressure-Tuning Interactions in Molecule-Based Magnets

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Chemistry

Abstract

In optimizing the properties of functional materials it is essential to understand in detail how structure influences properties. Identification of the most important structural parameters is time-consuming and usually investigated by preparing many different chemical modifications of a material, determining their crystal structures, measuring their physical properties and then looking for structure-property correlations. It is also necessary to assume that the chemical modifications have no influence other than to distort the structure, which is often not the case.
High pressure offers a way around these difficulties. Pressure can be used to distort a material without the need for chemical modification. Both crystal structures and physical property measurements can be conducted at high pressure, so that the properties of the same material can be studied in different states of distortion, providing the most direct way to study correlations between structure and properties.
In this proposal we focus on structure-property relationships in molecule-based magnets connected into extended chains, networks or frameworks using a combination of high pressure crystallography, magnetic measurements, spectroscopy and simulation which will exploit the UK's unique capabilities in extreme conditions research. Extended materials are of great interest because a small distortion at one site is propagated throughout the material by the strong chemical links between the magnetic centres, making the magnetic properties very sensitive to structural changes. We will design and build new instruments for magnetic susceptibility and diffraction measurements at high pressure and low temperature and we will exploit these new instruments and methodology to study two important classes of magnetic material.
1-D magnetic materials represent a fertile playground for discovering and understanding exotic physical phenomena. The magnetic behaviour of Single-Chain Magnets (SCMs) is fundamentally governed by the magnitude of nearest neighbour exchange interactions (intra-chain exchange), the extent of inter-chain interactions, and Ising-like anisotropy - all of which are sensitive to pressure. We have already shown that these parameters can be pressure-tuned in Single-Molecule Magnets (SMMs) and the same should be true for SCMs In 3-D frameworks magnetism can be combined with porosity, so that inclusion of different guest molecules provides another means for controlling magnetic properties. Prussian Blue Analogues consist of different metal cations linked by cyanide anions, while metal carboxylates build diamond-like frameworks. In both cases guest molecules influence magnetic ordering temperatures. Some metal-organic frameworks show spin-crossover behaviour, where different electronic configurations of the metal ions are stable under different conditions. The transition from one form to another is influenced by guest molecules which occupy the pores of the framework. High pressure will enable us to control the structure of the framework itself, the interactions between the host and the guest, and the number of guest molecules incorporated into the pores, providing a quantitative link between host-guest interactions and magnetism.

Planned Impact

The proposed programme is highly interdisciplinary in its scope, encompassing synthetic chemistry through to quantum physics and engineering, with a focus on the technically highly demanding area of extreme conditions. It provides an outstanding opportunity for the three researchers employed who will benefit from training in the most up-to-date scientific methodologies, publishing their work in the highest impact journals and presenting their work at an ambitiously broad range of conferences. Their skills will be broadened by proposal writing, (e.g. beamtime applications) and taking part in public engagement activities (see below). They will receive training outside the academic environment in the form of industrial internships which will provide valuable experience of working in the commercial sector. We have an outstanding record in training, and this has been recognised in the professional success of staff previously employed on our grants, including prizes and fellowships. The training the research staff will receive will make them extremely valuable for the UK economy, skilled in the most up-to-date research techniques, problem solving, writing for both publications and applications, presentation of work to specialists and non-specialists, trained in leadership and entrepreneurship with experience in academia, at central facilities and in the commercial sector.
Though extreme conditions research is most actively pursued in academia, our aim in this programme is to demonstrate its power in defining structure-property relationships. Providing a mechanism for determining how a structure should be tuned to optimize a particular property will find direct applications in industries that make use of materials science (electrical conductors, pressure-sensitive materials for security applications, catalytic applications of porous materials). The engineering expertise and the skills in design for extreme conditions are also of value to industries such as aerospace, renewable energy and advanced machining. Pressure is a more powerful thermodynamic variable than temperature and its potential for direct application in manufacturing processes is huge. It is already extensively used in materials synthesis and food processing, but we envisage that application in fine chemicals production and catalysis are realizable in the 10-15 year time-scale. This is the driver for fundamental extreme conditions research in the Chemical Sciences, and this growing interest is served by private-sector manufacturers of research instrumentation and software, several of whom are involved in our programme as hosts for internships. For example, we are working with the Cambridge Crystallographic Data Centre on methods, inspired by our work in high pressure, for the calculation of intermolecular interaction energies and visualisation of voids.
Our experience is that generation of very high pressures and the effect these have on materials rapidly attracts the interest of participants at public engagement activities. We regularly take on high-school students and undergraduates in summer projects based on our research and many of these have gone on to take science degrees or PhDs. We exploit the broad range of public engagement activities currently available in the three centres involved in this proposal to provide training in the ways to optimise presentation of complex material to the public to achieve greatest impact, a skill which will also prove extremely valuable in any profession.

Publications

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Binns J (2016) A non-topological mechanism for negative linear compressibility. in Chemical communications (Cambridge, England)

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Clegg JK (2017) Reversible Pressure-Controlled Depolymerization of a Copper(II)-Containing Coordination Polymer. in Chemistry (Weinheim an der Bergstrasse, Germany)

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Craig GA (2015) A high-pressure crystallographic and magnetic study of Na5[Mn(l-tart)2]·12H2O (l-tart = l-tartrate). in Dalton transactions (Cambridge, England : 2003)

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Decaroli C (2015) (C4H12N2)[CoCl4]: tetrahedrally coordinated Co2+ without the orbital degeneracy. in Acta crystallographica Section B, Structural science, crystal engineering and materials

 
Description The central idea of this project is that we can understand the connection between the magnetic properties of a material and its structure by compressing or distorting geometry with high pressure and at the same time measuring how the magnetic properties change. We have recently shown that in two mononuclear Re complexes compression of intermolecular ligand-ligand contacts leads to a linear increase in the long-range magnetic ordering temperature. In one case the temperature increase by a factor of approximately four. This work has recently been the subject of a highlight on the Diamond Synchrotron web-site (see URL link below) and a talk at Diamond Light Source. The work is published in Nature Communications. 7, 13870 (2016).

In work on the sodium salt of a manganese tartrate complex the effect of high pressure was focussed entirely arounf the sodium sites in the structure.This result opens-up a new strategy for directing the effects of compression towards specific moieties by incorporating them them in a rigid framework. This work is available in Dalton Transactions. 44, 42, p. 18324-18328 (2015).

In addition to work on structure-property relationships in specific materials we have also made some key methodological advances.

Many of the properties of molecular magnets are low-temperature phenomena and it is highly desirable to measure structure under the same conditions. Until now this has been extremely difficult because pressure cells are bulky devices that are hard to cool. We have developed the first 3D printed pressure cell which is small enough to be accommodated in commonly available open-flow cryostats available most crystallographic labs. The key development was to recognise that the screw-threads that connect the two halves of the pressure cell together can be idealised and miniaturised more readily using 3D printing than by conventional machining. The work is described in Review of Scientific Instruments. 88, 035103 (2017). For even lower temperatures it is now possible via our link with Newcastle University to measure high-pressure data near absolute zero.

Neutron diffraction is an important method for studying molecular materials, especially in cases the H-atom positions are important or information of magnetic ordering is required. Until now neutron experiments required much larger crystals than X-ray methods. However we have shown that use of neutron Laue methods yield data suitable for fully anisotropic structure refinement, allowing joint spectroscopic and X-ray and neutron diffraction studies of exactly the same sample. The penetrating powder of neutrons also means that the pressure cell can be accommodated in a cryostat, also enabling temperatures close to absolute zero to be accessed for high pressure measurements. This work is described in IUCrJ. 3, 3, p. 168-179 and was the subject of an internship by one of our team at the ANSTO neutron facility in Sydney.
Exploitation Route The findings described above have potential applications in using pressure to control of desirable physical properties and to identify the structural distortions needed to promote specific properties. We have focussed on magnetism, but the methods are applicable to any property, e.g. conductivity or spectroscopic response. We continue to make developments at central facilities that are used by numerous other groups.
Sectors Chemicals,Manufacturing, including Industrial Biotechology

URL http://www.diamond.ac.uk/Science/Research/Highlights/2017/high-pressure-magnetism.html
 
Description This grant formed the basis for basis of training three PDRAs in the most up-to-date scientific methodologies and techniques, both in the home-lab and at central facilities (mostly Diamond, but also ISIS). These techniques involved not only intricate experimental manipulations, but also the analysis of the large data sets which the instrument produces (e.g. variations of bond distances or intermolecular contacts across a pressure series) and placing these in the context of other materials, the variation of magnetic and spectroscopic properties measured using other techniques and computational modelling. The staff hired on the grant drafted the publications reporting their data and presented their work at conferences. This combination of training in advanced experimental techniques, the ability to pull conclusions out of large sets of disparate data and presentation of the results in a concise manner are highly transferable skills which have resulted in rapid recruitment into employment in intellectual property, software development and an international research fellowship. Public engagement was exemplified by presentations at the Scottish Schools Education Research Centre (SSERC) teachers' course and Dunfermline, a Webinar given in collaboration with SSERC and the Diamond light source as well as demonstrations to public audiences through open days. Software written for diffraction image processing and conversion, which continued to be developed over this grant, is used by commercial organisations including Bruker AXS and Incoatec, as well as by numerous other users of beamline I19 at Diamond.
First Year Of Impact 2017
Sector Chemicals,Digital/Communication/Information Technologies (including Software),Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description ANSTO PhD Studentship
Amount £59,700 (GBP)
Organisation Australian Nuclear Science and Technology Organisation 
Sector Public
Country Australia
Start 09/2017 
End 08/2020
 
Description FORTRESS: F block Covalency and Reactivity Defined by Structural Compressibility
Amount £812,957 (GBP)
Funding ID EP/N022122/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2016 
End 03/2019
 
Description Interactions of Small Molecules with Molecular Solids.
Amount £31,500 (GBP)
Organisation Advanced Light Source 
Sector Private
Country United States
Start 09/2015 
End 08/2018
 
Description Interpretation of the crystal structures of organometallic compounds
Amount £32,500 (GBP)
Funding ID 1797302 
Organisation Cambridge Crystallographic Data Centre 
Sector Academic/University
Country United Kingdom
Start 09/2016 
End 08/2019
 
Description Putting the Squeeze on Molecule-Based Magnets
Amount £1,632,535 (GBP)
Funding ID EP/N01331X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2016 
End 02/2021
 
Description Garry McIntyre 
Organisation Australian Nuclear Science and Technology Organisation
Country Australia 
Sector Public 
PI Contribution Samples and design and manufacture of diamond anvil cells
Collaborator Contribution Single-crystal neutron Laue diffraction
Impact Papers as listed
Start Year 2008
 
Description Joan Cano 
Organisation University of Valencia
Country Spain 
Sector Academic/University 
PI Contribution Structural and magnetic characterision of molecule-based magnets at high pressure
Collaborator Contribution Theoretical modelling of molecule-based magnets at high pressure
Impact Papers as listed
Start Year 2016
 
Description Prof. Rafael Valiente 
Organisation University of Cantabria
Country Spain 
Sector Academic/University 
PI Contribution Determination of structural and magnetic properties of molecule-based magnets at extreme conditions
Collaborator Contribution Determination of spectroscopic properties of molecule-based magnets at extreme conditions
Impact Publications as listed.
Start Year 2010