Organic molecular magnets leave the glove box.

In the not too distant future, we may be using organic magnets to pin shopping lists to the refrigerator. The advantage of organic magnets is that they can be made into a variety of sizes and shapes controlled by simple solution-based casting methods. However, the very few organic radicals that are stable enough to become magnets are typically air and moisture sensitive and stop behaving as magnets at temperatures above a few tens of Kelvins.

Recently, University of Victoria's Robin Hicks, MCIC, and post-doc Rajsapan Jain, as well as post-doc Khayrnl Kabir, grad student Joe B. Gilroy, MCIC, and collaborators Keith A. R. Mitchell, FCIC, and Kin-ChunK Wong from The University of British Columbia have discovered a new class of molecules that exhibit magnetic behaviour far above room temperature (Nature 445 (2007), 291). In contrast to previously reported molecular magnets, their compounds have an unusual 2:1 metal to ligand ratio and also are comparably stable at ambient conditions.

The materials were prepared by reaction of the ligands 1-3 with bis(1,5-cyclooctadiene) nickel under an argon atmosphere. Exposure of the resulting intermediate to air and humidity then led to the amorphous product (see Figure 4).

[FIGURE 4 OMITTED]

Infrared spectroscopy showed that in the product the ligands are present as radical anions, while X-ray photoelectron measurements showed that nickel is in its (+ 2) oxidation state. This means the magnetism cannot arise simply from elemental nickel, itself a ferromagnet. The team found that all three compounds show spontaneous magnetization and a distinctive hysteresis when exposed to a changing external magnetic field--indicative of long-range magnetic ordering, not unlike inorganic magnets.

Cathleen Crudden, MCIC, and Haas-Peter Loock, MCIC, are both associate professors of chemistry at Queen's University in Kingston, ON.