Designing Highly Axial Lanthanide Single Molecule Magnets

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For over fifty years economic factors have driven a steady trend of making electronic devices smaller. However, the rate of progress in miniaturisation has started to stall, and it has been predicted that a plateau may be reached within ten years. As such, "bottom-up" alternatives are sought to rival the current "top-down" approach to ensure continued technological advancement. One promising solution for high-density data storage is to use Single Molecule Magnets (SMMs). These are molecules that can store magnetic information, and could therefore give the smallest possible devices.Lanthanide (Ln) SMMs have emerged as leading candidates due to their favourable magnetic properties, but at present these only function with expensive liquid helium cooling. The temperatures at which Ln SMMs retain magnetic information are dictated by the choice of Ln, the molecular geometry, and the competition of magnetic relaxation pathways. These factors can all potentially be controlled but at present the relaxation mechanisms are still poorly understood. Relaxation processes can significantly lower the temperature at which magnetic information is retained, based on what would be predicted solely from consideration of a specific Ln with a well-defined geometry.As such, the syntheses of Ln SMMs with ideal metal/geometry arrangements are targeted, as these will give the maximum thermal barrier to magnetic relaxation. Once control of molecular geometry and optimal barriers are obtained, the magnetic relaxation pathways of these systems can be studied in depth over a large temperature range. Such a study has not previously been attempted on Ln SMMs. This will allow us to deepen our understanding of the factors dictating relaxation mechanisms, so that in future we can design Ln SMMs that disfavour such processes and can store magnetic information at even higher temperatures.It has been predicted by calculations that dysprosium(III) SMMs with only two donor atoms set opposite to each other (a two-coordinate, perfectly axial environment) will give the largest barriers to thermal magnetic relaxation. These systems could operate above liquid nitrogen temperatures, at which point they would become technologically viable. Ln ions prefer high coordination numbers and two-coordinate Ln(III) complexes are currently unknown, hence this would be a remarkable synthetic achievement.In recent work, we have reported a six-coordinate Dy(III) SMM with an environment that effectively mimics the axial system we seek, and yielded a world-record barrier to magnetic relaxation (Chemical Science, 2016, 7, 155). We have made theoretical predictions for improvements to the design of this system to raise this barrier even further, and have set out synthetic routes to achieve this goal in this proposal. More ambitiously, we target the synthesis of chemically feasible two-coordinate Dy(III) SMMs, following our predictions that these could exhibit magnetic relaxation above liquid nitrogen temperatures (Inorganic Chemistry, 2015, 54, 2097). We have recently reported the synthesis of a rare two-coordinate Ln(II) complex with a near-linear geometry (Chemical Communications, 2015, 7, 155), hence we are in an ideal position to transfer these methodologies and prepare the first two-coordinate Dy(III) SMMs.All synthetic studies in this proposal will be complemented by high level physical analysis of magnetic and electronic properties, including computational modelling. This will provide essential information to guide our pioneering studies of magnetic relaxation pathways and their relationship to the geometry and electronic structure of Ln SMMs. Ideally we may synthesise a Dy(III) SMM that can operate at liquid nitrogen temperatures.