First isolation of stable solid-state bismuth radical

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.