Yes, preparation of practical organic magnet remains a very difficult, challenging problem. Many may believe it is impossible, some may have doubt, some may say–waste of time! It is not easy to go against the nature…those electrons are happy to be paired, coupled their spins in opposite direction (antiferromagnetic coupling), forming chemical bonds, so why bother… Like most of us, loneliness is hard, so most going with the mainstream. Look at the history, Mose Gomberg got scoffed at for his report on the triarylmethyl radical in 1900 and he had to fight for over the period of 15 years to defense the free radical concept. And we all know the impact of his discovery, but no, Gomberg is not on the list of Nobel Laureates in Chemistry1. One thing I wonder though, why Gomberg ended his paper with this interesting statement.
(M. Gomberg, “An Instance of Trivalent Carbon: Triphenylmethyl’’, J. Am. Chem. Soc, 1900, 22, 757-771 doi:10.1021/ja02049a006)
Beside that strange statement, Gomberg’s courage gives us motivation to forge forward, toward the ultimate goal of organic magnet. It has been a long and tough road but we have made good progress.
At the current stage, we know more or less how to rational design structures with a large number of strongly interacting unpaired electrons that give rise to net ferromagnetic couplings (Magnetic Ordering in an Organic Polymer, Science, 2001, 294, 1503-1505, doi:10.1126/science.1065477). It took us 13 years to get this far, 101 years since Gomberg reported the first organic radical. Here is the timeline of the development2
The triarylmethyl polyradicals are unstable; they have to be handled at below 170 K in absence of oxygen. The magnetic ordering temperature of the triarylmethyl-based polymer at 10K is too low for any application. To make a practical material, we must implement the structure design with organic radicals (spin units) that are stable at normal working condition (on air at room temperature), while maintaining strong ferromagnetic couplings to reach ordering temperature above room temperature. These are two critical benchmarks we are striving to obtain.
There are only a few known highly stable organic radicals. Currently, we are working on the nitroxides and aminyls, following the bottom-up approach to prepare and study high-spin polyradicals that are stable on air at room temperature. Once again, we will learn, step by step, laying a solid foundation. We hope to find a way to reach our ultimate goal of an organic magnet that we will stick on our refrigerator doors…. Along the way, we will take advantage of what we have learned to prepare various nitroxides and aminyls that process good solubilities in aqueous solutions and investigate them for magnetic resonance imaging (MRI and EPRI) applications. For more information, visit this site.
1Interesting discussion about this subject: Lennart Eberson, “Gomberg and the Nobel Prize”, Advances in Physical Organic Chemistry, 2001, 36, 59-84.
2Learn more about this development here and here (the site is old and should be updated soon) and from the following review articles: A. Rajca, “The Physical Organic Chemistry of Very High-Spin Polyradicals”, Adv. Phys. Org. Chem., 2005, 40, 153-199; N M Shishlov, “From the Gomberg radical to organic magnets“, Russ Chem Rev, 2006, 75, 863-884 doi:10.1070/RC2006v075n10ABEH003621.