A Coordination Chemistry Approach to the Synthesis of Single-Molecule Magnets

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In this project, funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Jeffrey Long of the Department of Chemistry at the University of California, Berkeley is designing and synthesizing new single-molecule magnets. Single-molecule magnets are molecules that behave as nanoscale magnets at low temperatures and can display magnetic properties akin to both classical and quantum systems. A potential direct application of this work is in the fields of magnetic data storage, quantum computing, and spintronics, however the knowledge gained by understanding magnetic properties on the molecular level is applicable to a wide variety of magnetic materials. Single-molecule magnets typically only operate at very low temperatures (less than 60 K). The goal of this project is to synthesize new molecules which have even higher operating temperatures. The project lies at the interface of inorganic chemistry, coordination chemistry, and physics. Both Professor Long and the members of his group are active in disseminating their work to a broad scientific audience, and the graduate students in the group participate in programs which place them in local elementary and middle school classrooms for hands-on science lessons. Single-molecule magnets are molecules with magnetically bistable ground states. When thermal energy is small relative to the thermal barrier between these states the magnetic molecule can retain its magnetization in the absence of an applied field. The proposed research adopts three strategies to synthesize single-molecule magnets which operate at higher temperatures. The first is to design systems with enhanced magnetic anisotropy, which will increase the thermal barrier to magnetic relaxation. Highly axial coordination environments will be employed for both transition metal and lanthanide complexes to achieve higher magnetic anisotropy. The second strategy is to utilize strong magnetic coupling to mitigate the effect of relaxation processes which shortcut the thermal barrier. Both transition metal and lanthanide complexes will be coupled with radical bridging ligands that promote strong metal-radical magnetic exchange. For transition metal complexes, direct metal-metal interactions will also lead to strongly coupled magnetic centers. Additionally, mixed 3d-4f systems will be developed to take advantage of both the large magnetic anisotropy of the lanthanides and the strong exchange coupling of the transition metals. Finally, the third strategy will place magnetically anisotropic moieties in the rigid coordination environments of metal-organic frameworks. In this manner it may be possible to minimize the effects of low energy lattice vibrations in causing through-barrier magnetic relaxation pathways.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.