In this project funded by the Inorganic, Bioinorganic, and Organometallic Chemistry Program of the Chemistry Division and cofunded by the Office of International Science and Engineering, Stephen O. Hill of Florida State University will collaborate with Euan Brechin of the University of Edinburgh, United Kingdom to study the effect of high pressure on the magnetism of mononuclear and polynuclear complexes via the combination of x-ray structural data and high frequency EPR (electron paramagnetic resonance) data. The application of high pressure to complexes will allow the researchers to correlate structural changes with magnetic properties within the same molecule. The determination of such magnetostructural correlations will provide a fundamental insight into the electronic properties of monomeric and polynuclear complexes that form the basis for molecular magnetism studies. The PIs also propose to conduct workshops on high pressure, high field magnetic resonance techniques.
The goals of this International Collaboration in Chemistry (ICC), sponsored by the Inorganic, Bioinorganic, and Organometallic Chemistry Program of the Chemistry Division and co-funded by the Office of International Science and Engineering, have been to examine the effects of pressure on molecule-based magnets ranging from simple monomers and dimers (containing just one or two magnetic ions), to more complex polynuclear clusters (so-called single-molecule magnets – SMMs) and extended magnetic network materials. The use of pressure offers the potential to provide detailed information concerning correlations between structure and magnetic properties within the same material. The strategy has involved looking for such correlations by combining structural (X-ray) and magnetic characterization techniques with High-Field Electron Paramagnetic Resonance (HFEPR), all under high-pressure. The collaboration involved researchers in the Department of Physics at Florida State University and the National High Magnetic Field Laboratory (NHMFL), with overseas counterparts in the Department of Chemistry at the University of Edinburgh in Scotland. High-pressure HFEPR studies were performed in Florida, while X-ray structural studies were performed in the UK. The project initially involved a successful instrument development phase, resulting in a reliable platform for performing single-crystal, multi-high-frequency HFEPR studies as a function of pressures up to 30 kbar (30,000x atmospheric pressure). In fact, two setups have been developed that can operate in parallel at the NHMFL, and these are now available to users of the facility upon submission of a two-page proposal that is subject to peer review. One of the two high-pressure HFEPR spectrometers employs a 9/5/1 T superconducting vector magnet system, resulting in a truly unique capability (even for ambient pressure HFEPR) that allows for very precise two-axis alignment of the applied magnetic field relative to a crystal. Several distinct high-pressure HFEPR results have been achieved. In most cases, these have been complemented by X-ray data under high pressures. The findings have been disseminated in scientific journals and in the form of presentations at many international conferences. As a result, the project PI has been inundated with requests from potential users of this unique instrumentation. Therefore, activities initiated under this award are expected to continue through the support of the NHMFL HFEPR users program. Molecular magnetism represents a multidisciplinary research field that focuses on the employment of molecular approaches to create new magnetic materials in which properties can be tuned at the molecular level. Molecular magnets show considerable promise in terms of possible applications, as well as exhibiting many fascinating properties of fundamental importance. HFEPR under pressure can provide crucial spectroscopic information concerning interactions that control magnetism. Up to now, there have been few ambient pressure magnetostructural correlations for compounds containing more than two magnetic ions, and none whatsoever for any molecular species under external pressure. The combination of high-pressure X-ray, magnetometry and HFEPR is unique, allowing researchers to equate changes in structure to changes in magnetic response, i.e. magnetostructural correlations. One area of study involved organic magnets that have been researched extensively as potential alternatives to the more traditional device materials (silicon, copper, iron, etc..). This interest has been driven by the advantages organic materials offer in terms of their light-weight, bio-compatibility, and the tremendous synthetic control that can be achieved. Examples of organic magnets are quite rare, particularly ones that retain their magnetization after a polarizing magnetic field is removed. In fact, the idea of essentially plastic magnets breaks with the beliefs of many in the magnetism community. Nevertheless, this project has made important breakthroughs, involving both experiment and theory, through study of a family of compounds that hold records for both the highest operating temperatures and their ability to retain their magnetization. In fact, in terms of the latter property, these new materials may be compared to some of the best known elemental magnets such as cobalt, and they are orders of magnitude better than previously discovered organic magnets. Another area of study revealed the crucial importance of hydrogen-bonding in terms of dictating the magnetic properties of extended molecule-based magnetic network materials. The project provided extensive educational opportunities for students and postdocs. The Florida team made two extended visits to Edinburgh: on the first occasion, the PI, co-PI and one graduate student participated in a molecular magnetism workshop and interacted with the crystallography group; on the 2nd occasion, a postdoc and a different student spent six weeks working in Edinburgh. Two student/postdoc workshops were also organized in Florida; both were attended by the entire Edinburgh group, consisting of two postdocs and three graduate students. The Edinburgh and Florida teams also met twice at the International Conference on Molecule-based Magnets. Two of the Florida students who participated in the project from the start have now graduated and gone on to postdoctoral positions (one of them at the University of Oxford); the postdoc has also started a 2nd postdoctoral position at Los Alamos National Lab.
