Slow Magnetic Relaxation in Uranium(III) and Neodymium(III) Cyclooctatetraenyl Complexes

The synthesis, structure, and magnetic properties of a uranium(III) sandwich complex, [Li(DME)(3)][U-III(COT)(2)] (COT = bis(trimethylsilyl)cyclooctatetraenyl dianion), and its coordinatively analogous tetravalent equivalent, [U-IV(COT)(2)], were investigated. Additionally, a full structural and magnetic comparison to the isostructural and isoelectronic lanthanide complex, [Li(DME)(3)][Nd-III(COT)(2)], is provided. DFT calculations reveal that the U-III complex leads to weaker ligand-to-metal donation as compared with the tetravalent equivalent complex. Alternating current magnetic susceptibility results reveal slow magnetic relaxation in both U-III and Nd-III complexes. The enhanced magnetic performance of the U-III congener further encourages the use of actinides in the design of single-molecule magnets.