The benzophenone ketyl radical is well known for its deep-blue color when dissolved in organic solvents such as THF or toluene. These solvents are routinely dried in laboratories by continuous distillation with added amounts of of two components: benzophenone and sodium metal. They react to the ketyl which in turn reacts with any water thus drying the solvent. As long as the solvent does not turn blue it still contains water and the chemist has another cup of coffee.
For some incomprehensible reason no one has ever tried to isolate the ketyl compound (first observed in 1891 DOI) from this solution, that is until now! After no doubt tinkering a lot with the exact solvent composition (a mixture of diethyl ether and THF) and waiting patiently, Scott et al. (2008 DOI) were able to drag out crystals of K(Ph2CO) which were then analysed by x-ray crystallography. Main feature: a K4O4 cubane cage central core.
The discoverers are confident they can market solid K(Ph2CO) as a new chemical reagent.
Thomas A. Scott, Betty A. Ooro, David J. Collins, Michael Shatruk, Andrey Yakovenko, Kim R. Dunbar, Hong-Cai Zhou (2009). After 118 years, the isolation of two common radical anion reductants as simple, stable solids Chemical Communications (1) DOI: 10.1039/b815272a