Credit: © 2010 Wiley

In the quest for organic magnetic materials, attention has focused on preparing high-spin polyradicals, in particular by using moieties that enable intramolecular ferromagnetic coupling between free radicals. But even though triradical trimethylenebenzene has provided the framework for several such high-spin compounds, it has so far eluded characterization. Patrik Neuhaus and Wolfram Sander from the Ruhr University in Bochum, Germany, have now succeeded1 in isolating and characterizing it in an argon matrix.

The precursor tris(iodomethyl)benezene was subjected to flash vacuum pyrolysis at 480 °C. The products were subsequently isolated in an argon matrix, and characterized through infrared, UV–visible and electron paramagnetic resonance spectroscopy. These measurements revealed that the main product was a highly symmetrical triradical compound that possesses a quartet ground state, a description that fits the elusive trimethylenebenzene well. Derivatives bearing either one or two methyl groups rather than methylene radicals were also found to be present, but only as minor by-products.

The identity of the triradical was further supported by experiments carried out with deuterated methylene groups. It is also in good agreement with previous theoretical studies, which had shown that the triradical should possess both doublet and quartet spin states. Furthermore, in contrast to the widely used meta-dimethylenebenzene unit, the trimethylene derivative proved to be relatively stable to UV irradiation — an attractive property for the construction of magnets.