For the first time, researchers have managed to isolate a monomeric bismuth radical that is stable in the solid state.1 Overcoming problems of previous studies on heavy group 15 radicals, this new radical has been characterised by both electron paramagnetic resonance (EPR) and x-ray crystallography.

There are generally few observable stable radicals at the heavier end of group 15. Recent advances have resulted in isolable monomeric phosphorus radicals2, but radicals of heavier elements remain much more elusive. Only one antimony radical in solution has been observed by EPR, and bismuth has presented an even bigger challenge. Although a bismuth(II) radical was reported in 20143, it didn’t have an EPR signal and could not be characterised in the solid state.

In this study, the researchers managed to produce a bismuth(II) radical by reducing diamido bismuth(III) chloride with excess magnesium, affording a dark red crystalline solid of the radical with yields exceeding 80%. The paramagnetism and radical metal centre was confirmed by EPR. The team reports that if stored at room temperature under a dry nitrogen atmosphere, the solid radical will retain colour and crystallinity for around two weeks.