Science Concentrates INORGANIC CHEMISTRY
Single-molecule magnet breaks records Dysprosium complex brings high-density, molecularlevel data storage into the realm of possibility The quest for smaller and more energy-efficient smartphones and supercomputers with more features and processing power hinges on increasing data storage capacity. Two research groups at the University of Manchester have reported a dysprosium molecule with switchable magnetic properties—a single-molecule magnet (SMM) with the ability to store a single bit of data—that exhibits the most promise yet for reaching what might be the ultimate limit in high-denDy sity data storage. The catch with SMMs is their memory effect works only under the influence of a magnetic field at very low temperatures, up to 14 K so far, using liquid helium as a coolant. The new dysprosium molecule displays magnetic switchability up to 60 K, which is tantalizingly close to 77 K, liquid nitrogen’s temperature. Researchers who study lanthanide complexes tell C&EN this breakthrough could allow them to design even better molecules that could operate at 77 K or higher, which would make SMMs commercially practical for data servers. Such an achievement, they add, would be equivalent to the development of the first high-temperature superconductors operating at liquid nitrogen temperatures reported in the 1980s. Manchester’s Richard A. Layfield and coworkers reported dysprosocenium and its key magnetic properties on June 6 (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/ anie.201705426; paper submitted May 26). Manchester’s David P. Mills, Nicholas F. Chilton, and coworkers reported the same compound and properties on Aug. 23 (Nature 2017, DOI: 10.1038/nature23447; paper submitted April 21). The Mills and Chilton report additionally provides a theoretical explanation for how dysprosocenium achieves the enhanced magnetic effect. The Manchester researchers prepared the complex by sandwiching a dysprosium(III) cation between two cyclopentadienyl anions, each bearing three tert-butyl
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C&EN | CEN.ACS.ORG | SEPTEMBER 4, 2017
substituents, and crystallizing the borate salt. Maintaining the magnetic properties at higher temperature requires carefully designing molecules to control the symmetry of the lanthanide metal and its ligands, the researchers explain. In the case of dysprosium, which exhibits one of the highest magnetic moments + [B(C6F5)4]– of any element, an axial disposition of the ligands is favored over an equatorial arrangement. The cyclopentadienyl ligands achieve this distribution, but similar complexes containing additional ligands have been made before. What makes the new complex special, as Mills, Chilton, and coworkers explain, is exclusive binding of two cyclopentadienyl ligands to dysprosium and the coupling of the dysprosium ion’s magnetic moment with vibrations of the atoms within the complex, such as the C–H bonds of the tert-butyl groups. “These results represent an astounding leap forward from the previous temperature record and set the stage for realizing a magnetic memory effect at even higher temperatures through manipulation of the ligand field of low-coordinate lanthanide ions,” says SMM researcher Jeffrey R. Long of the University of California, Berkeley. “It is indeed a spectacular result for the field of molecular magnetism.” Molecular data storage using SMMs could handle more than 25,000 gigabytes of information on a device the size of a flash drive, the Manchester researchers note. That greatly exceeds the 256-GB data storage of today’s basic flash drives or Apple’s latest iPhone 7 that rely on magnetic nanoparticles. The publication of the new research in two papers in different journals by two research groups from the same university has left scientists following SMM chemistry scratching their heads. The researchers say they are not permitted to comment on the situation. The university’s press office tells C&EN that the university is investigating the irregularity and has no comment at this time.—STEVE RITTER
